Mammalian Hsp90 is a ubiquitous molecular chaperone that undergoes selective translation under stress. However, the precise control mechanism of HSP90 translation is yet to be elucidated. Polysome profiling has revealed that HSP90α mRNA is selectively translated, although global translation is inhibited during heat shock. A genetic screen identified two ribosomal proteins, RPL36A and RPL42, as translation regulators of yeast HSP90. I found that knockdown of either RPL36 or RPL36A, mammalian homologs of the yeast ribosomal proteins, modulates HSP90α expression under basal and heat shock condition, suggesting that the selective translation mechanism is conserved between humans and yeast. Profile expression in rhabdomyosarcoma cell line revealed a correlation between HSP90 protein levels and RPL36/RPL36A expression, suggesting that they might be the drivers behind elevated HSP90 expression. Interestingly, a higher level of RPL36 and RPL36A rendered cells less sensitive to HSP90 inhibitor, suggesting that they may be predictors of HSP90 inhibitor resistance.

Krebs ist die zweithäufigste Todesursache in Deutschland. Für die Behandlung von Tumorerkrankungen wird unter anderen die Strahlentherapie angewendet. Allerdings ist die Wirkung der Bestrahlung durch die Radiotoxizität auf normalem Gewebe sowie durch die Radioresistenz vieler Tumoren bei klinisch relevanten Dosen limitiert. Ein vielversprechendes Target für die Radiosensibilisierung von Tumorzellen scheint das Hitzeschockprotein HSP90 zu sein, ein wichtiges molekulares Chaperon, das für die Faltung, Aktivierung, Translokation und Degradation der so genannten Klientenproteine zuständig ist. Durch die pharmakologische Blockierung seiner Funktion wird die simultane Degradation multipler HSP90 Klientenproteine eingeleitet, darunter Radioresistenz-assoziierte Proteine wie RAF-1, AKT, EGFR, Survivin, DNA-Reparaturproteine. Verschiedene Studien belegen das Potential der HSP90 Inhibitoren Geldanamycin und seiner Derivaten als Radiosensibilisatoren. Im Gegensatz zu diesen Substanzen sind die neuartigen HSP90 Inhibitoren NVP-AUY922 und NVP-BEP800 wasserlöslich und nicht hepatotoxisch. Im ersten Teil der Arbeit wurde die Wirkung von NVP-AUY922 und NVP-BEP800 (200 nM, 24 h vor der Bestrahlung) auf die Strahlenempfindlichkeit humaner Tumorzelllinien unterschiedlicher Entitäten, darunter eine Lungenkarzinomzellinie A549, eine Fibrosarkomzelllinie HT1080, sowie zwei Glioblastomzelllinien GaMG und SNB19, untersucht. Die neuartigen HSP90 Inhibitoren zeigten in Kolonietest eine strahlensensibilisierende Wirkung in allen getesteten Tumorzelllinien. Weiterhin wurde mit diversen Methoden den Mechanismus der Radiosensibilisierung untersucht. Die HSP90 Inhibition erhöhte den Anteil der Zellen mit hypodiploiden DNA-Gehalt in den meisten untersuchten Tumorzelllinien. Außerdem induzierte die HSP90 Inhibition die Depletion der anti-apoptotischen Proteine AKT, pAKT und RAF-1 in allen Tumorzelllinien. Wie die erhöhte Expression von beiden Apoptosemarkern, aktivierte Caspase-3 und inaktiviertes PARP, nahe legt, wurde verstärkt die Caspase-abhängige Apoptose in den meisten untersuchten Tumorzelllinien nach HSP90 Inhibition eingeleitet. Laut Comet Assay induzierte die HSP90 Inhibition eine geringere DNA-Fragmentierung in bestrahlten Tumorzellen, gleichzeitig konnte aber eine langsamere Restitution der chromosomalen DNA festgestellt werden. Über die Messungen der γH2AX-Expression als Marker für DNA-Doppelstrangbrüche konnte eine erhöhte Induktion von DNA-Schäden nach HSP90 Inhibition und Bestrahlung sowie eine verlangsamte Reparatur der induzierten DNA-Schäden gemessen werden. Diese korrelierte mit der Depletion der DNA-Reparaturproteine KU70/KU80. Die HSP90 Inhibition führte zusätzlich zu einem ausgeprägten G2/M-Arrest, der durch die Bestrahlung verstärkt werden konnte. NVP-AUY922 induzierte außerdem eine Depletion der S-Phase. Die Depletion der Zellzyklus-regulierenden Proteine CDK1 und CDK4 sowie pRB korrelierte mit den beobachteten Zellzyklusstörungen. Die hier gewonnenen Ergebnisse verdeutlichen, dass der komplexe Mechanismus der Radiosensibilisierung nach HSP90 Inhibition die simultane Degradation diverser HSP90 Klientenproteine involviert, was verschiedene zelluläre Auswirkungen hat: verlangsamte Zellteilung durch anhaltende Zellzyklusstörungen, erhöhte DNA-Schäden und Verlangsamung der Reparatur der DNA-Schäden nach Bestrahlung sowie Apoptoseinduktion. Die HSP90 Inhibition induzierte gleichzeitig die Expression der Hitzeschockproteine HSP90 und HSP70, deren anti-apoptotischen Funktionen die radiosensibilisierenden Effekte der HSP90 Inhibitoren vermindern können. In dieser Arbeit wurden zwei Strategien getestet, um die Hochregulation von HSP90/HSP70 nach HSP90 Inhibition in den Tumorzelllinien A549 und GaMG zu unterdrücken. Zum einen wurden siRNAs gegen die stressinduzierbare α-Isoform von HSP90 angewendet, zum anderen wurde KNK437, eine Substanz die die Expression der HSP auf Transkriptionsebene unterdrückt, eingesetzt. Im zweiten Teil der Arbeit konnte gezeigt werden, dass die Transfektion mit siRNA gegen HSP90α gefolgt von NVP-AUY922 die Hochregulation von HSP90α um circa 50% unterdrückte. Allerdings wurde dadurch keine Erhöhung der NVP-AUY922-vermittelten Radiosensibilisierung erreicht. Es wurden außerdem keine signifikanten Veränderungen betreffend der Induktion und Reparatur der DNA-Schäden, Zellzyklusverteilung, Apoptoseinduktion sowie Expression der getesteten HSP90 Klientenproteine im Vergleich zu alleiniger HSP90 Inhibition festgestellt. Im dritten Teil der Arbeit konnte gezeigt werden, dass die simultane Behandlung mit NVP-AUY922 und KNK437 die NVP-AUY922-vermittelte Hochregulation von HSP90 und HSP70 in beiden Tumorzelllinien temporär unterdrückt. Obwohl die alleinige Behandlung mit KNK437 in der A549-Tumorzelllinie laut Kolonietest radiosensibilisierend wirkte, konnte die simultane Behandlung mit beiden Inhibitoren die NVP-AUY922-vermittelte Radiosensibilisierung nicht erhöhen. Obwohl die Unterdrückung der Stressantwort nach HSP90 Inhibition mittels KNK437 in beiden Tumorzelllinien einen anhaltenden G2/M-Arrest induzierte, blieb die Expression der anti-apoptotischen HSP90-Klientenproteine AKT und RAF-1 unverändert im Vergleich zu NVP-AUY922. Außerdem wurde die inhibierende Wirkung von NVP-AUY922 auf die Reparatur der strahleninduzierten DNA-Schäden nicht erhöht. Die hier gezeigten in vitro Ergebnisse unterstützen die Anwendung von NVP-AUY922 und NVP-BEP800 für in vivo Studien sowie in klinischen Studien alleine oder in Kombination mit der Bestrahlung. Unsere Arbeit ist von besonderem Interesse für die Strahlentherapie, da NVP-AUY922 bereits in klinischen Studien getestet wird. / Besides important improvement of tumor therapy, which increased the chance of survival for the patients, cancer remains the second cause of death in Germany. Among others, radiotherapy is one of the treatment options for tumor diseases. However, radiotherapy has some limitations due to the radiotoxicity on normal tissue and to the radioresistance of several tumors at therapeutic doses. One of the promising radiosensitizers of tumor cells seems to be the heat shock protein HSP90 – an essential molecular chaperone involved in folding, activation, translocation and degradation of its so called client proteins. The pharmacological inhibition of its chaperone function leads to simultaneous degradation of several HSP90 client proteins such as RAF-1, AKT, EGFR, survivin, DNA repair proteins and consequent disruption of several radioresistance-associated pathways. Several studies proved the radiosensitizing ability of geldanamycin and its derivates. In contrast to these drugs, the synthetic HSP90 inhibitors NVP-AUY922 and NVP-BEP800 are more water soluble and not hepatotoxic. In the first part of this work, we tested the effect of NVP-AUY922 and NVP-BEP800 (200 nM, 24 h prior irradiation) on the radiation response of tumor cell lines of different entities: the lung carcinoma A549, the fibrosarcoma HT1080 and the glioblastoma cell lines GaMG and SNB19. The colony forming assay revealed that pre-treatment with the novel HSP90 inhibitors increased the radiosensitivity of all tested tumor cell lines. Furthermore we investigated the mechanism of radiosensitization after HSP90 inhibition. HSP90 inhibition led to an increased percentage of tumor cells with hypodiploid DNA content (subG1 fraction) in most tested cell lines. Moreover, it led to the depletion of the anti-apoptotic HSP90 client proteins AKT, pAKT and RAF-1. In addition, it increased the pro-apoptotic caspase-3 and PARP cleavage in most of the tested cell lines. Our comet assay revealed a lower DNA fragmentation in drug-treated and irradiated tumor cells, but a slower restoration of DNA damage. Measurements of γH2AX expression as a sensitive marker for DNA-DSB showed an increased induction of DNA damage as well as DNA repair protraction in drug-treated and irradiated tumor cells. Inhibition of DNA repair after HSP90 inhibition was supported by the depletion of the DNA repair proteins KU70/KU80. Moreover the novel HSP90 inhibitors led to an increased G2/M-arrest, which could be enhanced by irradiation. In addition, NVP-AUY922 induced S-Phase depletion. The cell cycle disturbances correlated with the drug-mediated degradation of cell cycle regulating proteins CDK4, CDK1 and pRB. In conclusion, our results made clear that the complex mechanism of radiosensitization involves simultaneous degradation of several HSP90 client proteins, thus causing slower proliferation of the tumor cells due to dramatic cell cycle disturbances, increased DNA damage and protraction of DNA repair after irradiation as well as apoptosis induction. However, the radiosensitizing effect of the novel HSP90 inhibitors might be limited by the simultaneous drug-mediated induction of the expression of the anti-apoptotic heat shock proteins HSP90 and HSP70. In this study, we tested two strategies to suppress the drug-mediated up-regulation of HSP90 and HSP70 in the tumor cell lines A549 and GaMG. The first strategy was the siRNA-mediated down-regulation of the stress-inducible isoform HSP90α, combined with drug treatment and irradiation. The second strategy was the inhibition of the stress response by simultaneous treatment with the HSF-1 inhibitor KNK437. In the second part of this work we could show that pre-silencing of HSP90α followed by treatment with NVP-AUY922 indeed reduced the drug-mediated up-regulation of HSP90α to about 50%. However, it did not enhance the radiosensitizing effect of NVP-AUY922. In addition, it did not show any significant changes concerning the induction and the repair of DNA damage, the cell cycle distribution or the expression of the tested HSP90 client proteins AKT, RAF-1, CDK1 and CDK4 compared with drug-only treatment. In the third part of this work we could show that simultaneous treatment with NVP-AUY922 and KNK437 temporary suppressed the NVP-AUY922-mediated up-regulation of HSP90 and HSP70. Although treatment with KNK437 alone increased the radiosensitivity of A549 tumor cells as shown by colony forming assays, simultaneous treatment with both inhibitors did not increase NVP-AUY922-mediated radiosensitization in both tumor cell lines. Our cell cycle analyses revealed that the suppression of stress response after HSP90 inhibition by KNK437 led to a sustained G2/M-arrest in both tumor cell lines. However, the expression of the anti-apoptotic proteins AKT and RAF-1 remained unchanged compared with HSP90 inhibition alone. The evaluation of γH2AX expression showed that simultaneous treatment did not enhance NVP-AUY922-mediated inhibition of DNA repair after irradiation. Our in vitro results support the use of the novel HSP90 inhibitors in in vivo studies as well as in clinical studies alone or in combination with irradiation. This work is of particular interest for the radiation therapy of cancer, because the novel HSP90 inhibitor NVP-AUY922 is currently in clinical trials.

Drug resistance is one of the major impediments to control Plasmodium falciparum malaria worldwide. Heat shock protein 90 (Hsp90) is an essential component of the buffering capacity of eukaryotic cells as a part of the stress response. P. falciparum is no different and requires Hsp90 to chaperone proteins essential for cell cycle progression and drug resistance. Inhibition of P. falciparum Hsp90 (PfHsp90) may be able to not only cripple the parasite but also serve as an adjunctive antimalarial by circumventing drug resistance. The results presented in this thesis identify novel Hsp90 inhibitors that synergize with conventional antimicrobials, such as chloroquine (CQ), when used in combination. The objectives were to identify specific malaria Hsp90 inhibitors, the mechanism of the synergistic phenotype, and whether the strategy translates in vivo. To this end, the antimalarial activity of the purine analog PU-H71, and novel PfHsp90 inhibitors was tested. PU-H71 and the novel inhibitors APPA, harmine, and acrisorcin exhibited antimalarial activity in the nanomolar range and displayed synergistic activity with CQ. PU-H71 was able to reverse CQ resistance in a cell-based assay using the CQ-resistant strain W2. PU-H71 caused ring-stage arrest during the intra-erythrocytic cycle. Co-immunoprecipitation studies revealed that PfHsp90 interacts directly with the CQ resistance transporter (PfCRT). In the P. berghei mouse model of malaria, PU-H71 and harmine were able to reduce parasitemia and synergize with CQ. The interaction of PfHsp90 with PfCRT may underlie the synergistic phenotype. We conclude that PU-H71 and harmine are effective adjunctive antimalarial drugs that may be useful in combination therapies.

Drug resistance is one of the major impediments to control Plasmodium falciparum malaria worldwide. Heat shock protein 90 (Hsp90) is an essential component of the buffering capacity of eukaryotic cells as a part of the stress response. P. falciparum is no different and requires Hsp90 to chaperone proteins essential for cell cycle progression and drug resistance. Inhibition of P. falciparum Hsp90 (PfHsp90) may be able to not only cripple the parasite but also serve as an adjunctive antimalarial by circumventing drug resistance. The results presented in this thesis identify novel Hsp90 inhibitors that synergize with conventional antimicrobials, such as chloroquine (CQ), when used in combination. The objectives were to identify specific malaria Hsp90 inhibitors, the mechanism of the synergistic phenotype, and whether the strategy translates in vivo. To this end, the antimalarial activity of the purine analog PU-H71, and novel PfHsp90 inhibitors was tested. PU-H71 and the novel inhibitors APPA, harmine, and acrisorcin exhibited antimalarial activity in the nanomolar range and displayed synergistic activity with CQ. PU-H71 was able to reverse CQ resistance in a cell-based assay using the CQ-resistant strain W2. PU-H71 caused ring-stage arrest during the intra-erythrocytic cycle. Co-immunoprecipitation studies revealed that PfHsp90 interacts directly with the CQ resistance transporter (PfCRT). In the P. berghei mouse model of malaria, PU-H71 and harmine were able to reduce parasitemia and synergize with CQ. The interaction of PfHsp90 with PfCRT may underlie the synergistic phenotype. We conclude that PU-H71 and harmine are effective adjunctive antimalarial drugs that may be useful in combination therapies.

<p>Despite its ubiquitous abundance, Hsp90 inhibitors have shown promise in anti-cancer clinical trials, suggesting that Hsp90 inhibitors selectively target tumor cells while exhibiting minimal effects in normal cells. Extracellular expression of heat shock protein 90 (eHsp90) by tumor cells is strongly correlated with malignancy. Development of small molecule probes that can specifically detect eHsp90 in vivo may therefore have utility in the early detection of malignancy. We synthesized a fluorescent cell impermeable Hsp90 inhibitor, HS-131, to target eHsp90 in vivo. HS-131 was characterized biochemically to ensure specificity for eHsp90, and an inactive analog was also synthesized to be used as an in vivo control. </p><p>Through confocal microscopy, eHsp90 can be visualized with cell impermeable, fluorophore-tagged Hsp90 inhibitors. High resolution confocal and real time lattice light sheet microscopy showed that probe-bound eHsp90 accumulates in punctate structures on the plasma membrane of breast tumor cells and is subsequently actively internalized. This internalization occurs in the presence and absence of inhibitors. The extent of internalization correlates with tumor cell aggressiveness, and this process can be induced in benign cells by over-expressing p110HER2, leading to malignant transformation of these cells. Internalization of eHsp90 is also increased after inhibition of Hsp70, suggesting that overcompensation of the heat shock response can also upregulate the eHsp90 trafficking mechanism. Whole body 3D cryo fluorescence imaging and histology of flank and spontaneous tumor-bearing mice strongly suggests that eHsp90 expression is a unique phenomenon in vivo. </p><p>Taken together, these results suggest that active and differential internalization of eHsp90 in aggressive cancer cells contributes to the selectivity observed upon Hsp90 inhibitor treatment and may provide a novel metastatic biomarker for solid tumors and may lead to the development of a tumor-specific drug delivery system.</p> / Dissertation

As chaperonas moleculares são proteínas que auxiliam no enovelamento correto de outras proteínas, entre outras funções importantes para as células, motivo pelo qual elas têm sido alvo para o combate de várias doenças. As Hsp90 (82-96 kDa) são chaperonas abundantes que interagem com diversas proteínas-cliente. São constituídas por três domínios: N-terminal, intermediário ou central (M) e C-terminal, o qual é responsável pela dimerização da proteína. A atividade da Hsp90 está diretamente relacionada à sua atividade ATPásica. Durante o ciclo funcional, as Hsp90 podem interagir com inúmeras co-chaperonas. Uma delas é a co-chaperona p23 (18-22 kDa) que interage com o dímero da Hsp90 e algumas das suas funções são a inibição da atividade ATPásica e atividade chaperona. O objetivo do trabalho foi obter a proteína recombinante Hsp90 de Leishmania braziliensis e os domínios N e N+M, determinar fatores importantes que relacionam mudanças conformacionais e função da Hsp90 e as bases moleculares da inibição por GA. Também obter as co-chaperonas Lbp23A e Lbp23B e investigar a interação com a LbHsp90 e suas funções. As proteínas produzidas foram purificadas e caracterizadas por técnicas biofísicas. Em solução, a LbHsp90 foi caracterizada como dímero assimétrico e as demais proteínas como monômeros assimétricos.A interação da LbHsp90 e domínios com nucleotídeos foi analisada por fluorescência e as constantes de dissociação ficaram em torno de 150 &micro;M. A afinidade por GA foi maior que a verificada para ATP e em ordem crescente para LbHsp90, LbHsp90_NM e LbHsp90_N. A LbHsp90 apresentou grande atividade chaperona em relação à citrato sintase, de maneira independente de ATP. A LbHsp90 mostrou baixa atividade ATPásica, a qual foi inibida pela GA com IC50 de 0,7 &micro;M. Tanto a Lbp23A quanto a Lbp23B inibiram a atividade ATPásica da LbHsp90, porém a Lbp23A aproximou-se de 100% de inibição e a Lbp23B apenas 30%. A interação in vitro entre a LbHsp90 e a Lbp23B foi observada por pull-down na presença/ausência de nucleotídeos e essa técnica não se mostrou adequada para a Lbp23A.O pioneirismo do trabalho com a Hsp90/p23 de L. braziliensis oferece uma grande contribuição para futuros trabalhos que visam o entendimento das relações funcionais entre essas proteínas e o contexto das Hsp90 no desenvolvimento da leishmaniose. / Molecular chaperones are proteins involved in proper folding of other proteins, and others important cellular functions, why they have been targeted for combating various diseases. The Hsp90 (82-96 kDa) are ubiquitous chaperones that interact with a wide range of client proteins. They are formed by three domains: N-terminal, central or middle (M), and C-terminal, which is responsible by its dimerization. The Hsp90 activity is related to its ATPase activity. During the Hsp90 functional cycle, diverse co-chaperones. One of them is the p23 (18 kDa), that interacts with one Hsp90 dimer, and some p23 functions are the inhibition of Hsp90 ATPase activity and chaperone activity. The aim of this work was obtain the Hsp90 recombinant Leishmania braziliensis Hsp90, the N and N+M domains, to determine the important factors related to conformational changes and Hsp90 function, and the molecular basis of GA inhibition. Also, to obtain the Lbp23A and Lbp23B co-chaperones in order to establish relevant aspects for LbHsp90 interaction and its co-chaperones functions. The recombinant proteins were produced, purified and characterized by biophysics techniques. The LbHsp90 was identified as an asymmetric dimer for whereas the others were identified as asymmetric monomers. The interactions between LbHsp90 and domains with nucleotides were determined by fluorescence and the dissociation constants were about 150 &micro;M. The GA-affinity was greater than ATP one, in increasing order for LbHsp90, LbHsp90_NM, and LbHsp90_N. The LbHsp90 showed large chaperone activity related to citrate synthase independently of ATP. The LbHsp90 presented low ATPase activity, which was inhibited by GA with a IC50 of 0,7. The Lbp23A and Lbp23B inhibited the ATPase activity with different values, the Lbp23A inhibition was closed to 100% whereas the Lbp23B one was 30%. The in vitro interaction between the LbHsp90 and Lbp23B was observed by pull-down, in the absence or presence of nucleotides, and for Lbp23A this technique was not appropriated. The pioneering work with Hsp90/p23 from L. braziliensis offers an important contribution to future studies aimed at understanding the functional relationships between these proteins and the context of Hsp90 in the development of leishmaniasis.

As chaperonas moleculares são ativas em muitos processos celulares envolvendo o enovelamento e a homeostase de proteínas. Essas características fazem das chaperonas alvos potenciais para o tratamento de diversas doenças. As Hsp70 e as Hsp90, em especial, são proteínas ubíquas altamente conservadas biologicamente que atuam no enovelamento de proteínas nascentes, prevenção da agregação proteica, recuperação de proteínas de agregados, sinalização e crescimento celular, dentre outros. Contudo, para que essas proteínas cumpram eficientemente suas funções, elas devem ser moduladas por co-chaperonas moleculares. A SGT é uma co-chaperona que pode ser dividida em três regiões: domínio N-terminal, domínio TPR e domínio C-terminal, sendo que a região do domínio TPR é a responsável pela interação com o motivo EEVD no C-terminal das Hsp90 e Hsp70 citoplasmáticas. A SGT é encontrada em vários organismos, dentre eles os protozoários do gênero Leishmania spp.. Estes organismos são responsáveis pela leishmaniose, uma doença negligenciada que afeta milhares de pessoas todos os anos, principalmente em países subdesenvolvidos. Evidências indicam que a SGT em protozoários é essencial para o crescimento e viabilidade da forma promastigota. Diante disso, nesse trabalho foi feito o estudo estrutural e funcional da co-chaperona SGT de Leishmania braziliensis (LbSGT). A LbSGT recombinante foi produzida e purificada. A caracterização estrutural indica que a LbSGT é uma proteína rica em estrutura secundária do tipo hélice &alpha; que se comporta como um dímero alongado em solução. Dados de estabilidade térmica e química indicam que a LbSGT é uma proteína formada por domínios com diferentes estabilidades. A LbSGT foi identificada in vivo e o western blotting indicou sua presença cognata nas formas promastigotas do protozoário. Os ensaios de interação indicam que as interações entre a LbSGT e a Hsp90 de L. braziliensis (LbHsp90) e a LbSGT e Hsp70-1A humana (usada como proteína modelo) são diferentes da interação da LbSGT com o peptídeo MEEVD. Sendo assim, esses dados sugerem que a interação da LbSGT com a Hsp70-1A e LbHsp90 envolvem mais regiões das proteínas do que somente o motivo de interação da Hsp70-1A e da LbHsp90 com o domínio TPR da LbSGT. Em conjunto, as propriedades estruturais e funcionais da LbSGT observadas estão de acordo com a possível função da SGT como proteína adaptadora entre os sistemas Hsp70 e Hsp90 no foldossoma. / The molecular chaperones are active in many cellular processes involving protein folding and homeostasis. These characteristics make the chaperones potential targets to the treatment of many diseases. Hsp70 and Hsp90, in special, are highly conserved ubiquitous proteins that act in the folding of nascent proteins, protein aggregation prevention, aggregate recovering, signaling and cellular growth, among others. However, for these proteins to effectively fulfill their function, they must be modulated by molecular co-chaperones. SGT is a co-chaperone that can be divided into three domains: a N-terminal domain, a TPR domain and a C-terminal domain, being the TPR domain responsible for the interaction with the EEVD motif at the C-terminus of cytoplasmic Hsp90 and Hsp70. SGT is found in various organisms; among they are the protozoans of Leishmania spp.. These organisms are responsible for leishmaniasis, a neglected disease that affects thousands people every year, mainly at underdeveloped countries. Evidences indicate that SGT in protozoans are essential to the growth and viability of promastigote form. Therefore, the structural and functional study of the Leishmania braziliensis SGT (LbSGT) is presented. Recombinant LbSGT was produced and purified. The structural characterization points that LbSGT is rich in &alpha;-helix secondary structure and behaves as an elongated dimer in solution. Chemical and thermal stability data suggest that LbSGT is formed by domains of different stabilities. LbSGT was identified in vivo and the western blotting indicates its cognate presence in the protozoan promastigote forms. The interaction assays show that the interaction between LbSGT and Hsp90 of L. braziliensis (LbHsp90) or human Hsp70-1A (used as model protein) were different from the interaction between LbSGT with MEEVD peptide. Moreover, these data suggests that the interaction between LbSGT and Hsp70-1A and LbHsp90 involves additional protein regions besides the Hsp70-1A and LbHsp90 interaction motif. Altogether, the observed functional and structural proprieties of LbSGT accord to the SGT possible function as an adapter protein between the Hsp70 and Hsp90 systems in the foldossome.

A malária é a doença parasitária mais comum no mundo e é causada por protozoários do gênero Plasmodium spp., sendo transmitida por dípteros do gênero Anopheles spp. para hospedeiros vertebrados. Ambos, parasitas e vetores, têm desenvolvido resistência aos tratamentos e medidas profiláticas, respectivamente, indicando a necessidade de novas formas de controle. Chaperonas moleculares e co-chaperonas são interessantes alvos de estudo para desenvolvimento de terapias mais eficazes, uma vez que estas biomoléculas desempenham papel importante no processo de adaptação e sobrevivência do protozoário. As chaperonas da família Hsp90 participam de vários processos fisiológicos, que não somente auxiliar o enovelamento de proteínas clientes. Cada protômero da Hsp90 é composto por três domínios denominados N, M e C, e a proteína se organiza na forma de homodímeros flexíveis. As co-chaperonas são proteínas auxiliares, essenciais para modulação do ciclo funcional da Hsp90. A co-chaperona Aha1 (do inglês Activator of the Hsp90-ATPase activity 1) estabiliza a Hsp90 em um estado conformacional intermediário e estimula a atividade ATPásica da mesma. Neste contexto, é usual a busca por inibidores potenciais diretos e indiretos para Hsp90 e por respostas sobre seu mecanismo de inibição. O objetivo deste trabalho foi a obtenção e caracterização bioquímica e biofísica da proteína Hsp90 recombinante de Plasmodium falciparum (PfHsp90) e construções PfHsp90NM e PfHsp90M, além do mapeamento da interação com a co-chaperona Aha4 de P. falciparum (PfAha4). Os experimentos de caracterização estrutural revelam que o domínio N é menos estável termicamente do que o domínio M e também é o mais rico em estrutura secundária do tipo hélice &alpha;. A PfHsp90 comporta-se majoritariamente como homodímero alongado e flexível em solução, sendo o domínio C essencial para a dimerização, todavia as construções PfHsp90NM e PfHsp90M comportam-se como monômeros. Ensaios de fluorescência revelaram que as construções exibem diferenças na estabilidade química e que possuem estrutura terciária local com seus triptofanos parcialmente expostos ao solvente. A atividade ATPásica da PfHsp90 foi estimulada por PfAha4, e a interação entre elas foi resolvida com estequiometria de duas moléculas de PfAha4 por dímero de PfHsp90. Tal interação foi entalpicamente dirigida, ocorrendo liberação de moléculas de água, com interação mediada principalmente por contatos hidrofóbicos. O mapeamento das regiões de contato sugere que o cerne da interação ocorra entre a PfAha4 e o domínio M da PfHsp90. As diferenças exibidas pela PfHsp90 com relação as propriedades de proteínas ortólogas podem ter relação com os resíduos de aminoácidos que conectam os domínios N e M em sua estrutura, devido a sua flexibilidade, tamanho e composição. / Malaria is the most common parasitic disease in the world and is caused by protozoa of the genus Plasmodium spp., and transmitted by dipterans of the genus Anopheles spp. for vertebrate hosts. Both parasites and vectors have developed resistance to treatments and prophylactic measures, respectively, indicating the need for new forms of control. Molecular chaperones and co-chaperones are interesting targets for the development of more effective therapies, since these biomolecules play an important role in the process of adaptation and survival of the protozoan. The chaperones of the Hsp90 family participate in several physiological processes, which not only aid in the folding of client proteins. Each Hsp90 protomer have three domains called N, M and C, and the protein is organized as flexible homodimers. Co-chaperones are assistant proteins, they are essential for modulating the functional cycle of Hsp90. The Aha1 (Activator of the Hsp90-ATPase activity 1) co-chaperone stabilizes Hsp90 in an intermediate conformational state and stimulates the ATPase activity thereof. In this context, it is usual the search for direct and indirect potential inhibitors for Hsp90 and for responses about its inhibition mechanism. The objective of this work was the biochemical and biophysical characterization of the Hsp90 recombinant protein of Plasmodium falciparum (PfHsp90) and PfHsp90NM and PfHsp90M constructions, as well as to map interactions with the Aha4 co-chaperone of P falciparum (PfAha4). Structural characterization experiments show that the N domain is less thermally stable than the M domain and is also the richest in &alpha;-helix secondary structure. PfHsp90 behaves mostly as elongated and flexible homodimer in solution, domain C is essential for dimerization, on the other hand the constructs PfHsp90NM and PfHsp90M behave as monomers. Fluorescence assays revealed that the constructs exhibit differences in chemical stability and that have local tertiary structure with their tryptophans partially exposed to the solvent. The ATPase activity of PfHsp90 was stimulated by PfAha4, and the interaction between them was resolved with stoichiometry of two molecules of PfAha4 by PfHsp90 dimer. Such interaction was enthalpically driven, releasing of water molecules, with interaction mediated mainly by hydrophobic contacts. The mapping of contact regions suggests that the core of the interaction occurs between PfAha4 and the M domain of PfHsp90. The differences exhibited by PfHsp90 concerning the properties of orthologous proteins, may be related to the amino acid residues that connect the N and M domains in its structure, due to its flexibility, size and composition.

As chaperonas moleculares são ativas em muitos processos celulares envolvendo o enovelamento e a homeostase de proteínas. Essas características fazem das chaperonas alvos potenciais para o tratamento de diversas doenças. As Hsp70 e as Hsp90, em especial, são proteínas ubíquas altamente conservadas biologicamente que atuam no enovelamento de proteínas nascentes, prevenção da agregação proteica, recuperação de proteínas de agregados, sinalização e crescimento celular, dentre outros. Contudo, para que essas proteínas cumpram eficientemente suas funções, elas devem ser moduladas por co-chaperonas moleculares. A SGT é uma co-chaperona que pode ser dividida em três regiões: domínio N-terminal, domínio TPR e domínio C-terminal, sendo que a região do domínio TPR é a responsável pela interação com o motivo EEVD no C-terminal das Hsp90 e Hsp70 citoplasmáticas. A SGT é encontrada em vários organismos, dentre eles os protozoários do gênero Leishmania spp.. Estes organismos são responsáveis pela leishmaniose, uma doença negligenciada que afeta milhares de pessoas todos os anos, principalmente em países subdesenvolvidos. Evidências indicam que a SGT em protozoários é essencial para o crescimento e viabilidade da forma promastigota. Diante disso, nesse trabalho foi feito o estudo estrutural e funcional da co-chaperona SGT de Leishmania braziliensis (LbSGT). A LbSGT recombinante foi produzida e purificada. A caracterização estrutural indica que a LbSGT é uma proteína rica em estrutura secundária do tipo hélice &alpha; que se comporta como um dímero alongado em solução. Dados de estabilidade térmica e química indicam que a LbSGT é uma proteína formada por domínios com diferentes estabilidades. A LbSGT foi identificada in vivo e o western blotting indicou sua presença cognata nas formas promastigotas do protozoário. Os ensaios de interação indicam que as interações entre a LbSGT e a Hsp90 de L. braziliensis (LbHsp90) e a LbSGT e Hsp70-1A humana (usada como proteína modelo) são diferentes da interação da LbSGT com o peptídeo MEEVD. Sendo assim, esses dados sugerem que a interação da LbSGT com a Hsp70-1A e LbHsp90 envolvem mais regiões das proteínas do que somente o motivo de interação da Hsp70-1A e da LbHsp90 com o domínio TPR da LbSGT. Em conjunto, as propriedades estruturais e funcionais da LbSGT observadas estão de acordo com a possível função da SGT como proteína adaptadora entre os sistemas Hsp70 e Hsp90 no foldossoma. / The molecular chaperones are active in many cellular processes involving protein folding and homeostasis. These characteristics make the chaperones potential targets to the treatment of many diseases. Hsp70 and Hsp90, in special, are highly conserved ubiquitous proteins that act in the folding of nascent proteins, protein aggregation prevention, aggregate recovering, signaling and cellular growth, among others. However, for these proteins to effectively fulfill their function, they must be modulated by molecular co-chaperones. SGT is a co-chaperone that can be divided into three domains: a N-terminal domain, a TPR domain and a C-terminal domain, being the TPR domain responsible for the interaction with the EEVD motif at the C-terminus of cytoplasmic Hsp90 and Hsp70. SGT is found in various organisms; among they are the protozoans of Leishmania spp.. These organisms are responsible for leishmaniasis, a neglected disease that affects thousands people every year, mainly at underdeveloped countries. Evidences indicate that SGT in protozoans are essential to the growth and viability of promastigote form. Therefore, the structural and functional study of the Leishmania braziliensis SGT (LbSGT) is presented. Recombinant LbSGT was produced and purified. The structural characterization points that LbSGT is rich in &alpha;-helix secondary structure and behaves as an elongated dimer in solution. Chemical and thermal stability data suggest that LbSGT is formed by domains of different stabilities. LbSGT was identified in vivo and the western blotting indicates its cognate presence in the protozoan promastigote forms. The interaction assays show that the interaction between LbSGT and Hsp90 of L. braziliensis (LbHsp90) or human Hsp70-1A (used as model protein) were different from the interaction between LbSGT with MEEVD peptide. Moreover, these data suggests that the interaction between LbSGT and Hsp70-1A and LbHsp90 involves additional protein regions besides the Hsp70-1A and LbHsp90 interaction motif. Altogether, the observed functional and structural proprieties of LbSGT accord to the SGT possible function as an adapter protein between the Hsp70 and Hsp90 systems in the foldossome.

As chaperonas moleculares são proteínas que auxiliam no enovelamento correto de outras proteínas, entre outras funções importantes para as células, motivo pelo qual elas têm sido alvo para o combate de várias doenças. As Hsp90 (82-96 kDa) são chaperonas abundantes que interagem com diversas proteínas-cliente. São constituídas por três domínios: N-terminal, intermediário ou central (M) e C-terminal, o qual é responsável pela dimerização da proteína. A atividade da Hsp90 está diretamente relacionada à sua atividade ATPásica. Durante o ciclo funcional, as Hsp90 podem interagir com inúmeras co-chaperonas. Uma delas é a co-chaperona p23 (18-22 kDa) que interage com o dímero da Hsp90 e algumas das suas funções são a inibição da atividade ATPásica e atividade chaperona. O objetivo do trabalho foi obter a proteína recombinante Hsp90 de Leishmania braziliensis e os domínios N e N+M, determinar fatores importantes que relacionam mudanças conformacionais e função da Hsp90 e as bases moleculares da inibição por GA. Também obter as co-chaperonas Lbp23A e Lbp23B e investigar a interação com a LbHsp90 e suas funções. As proteínas produzidas foram purificadas e caracterizadas por técnicas biofísicas. Em solução, a LbHsp90 foi caracterizada como dímero assimétrico e as demais proteínas como monômeros assimétricos.A interação da LbHsp90 e domínios com nucleotídeos foi analisada por fluorescência e as constantes de dissociação ficaram em torno de 150 &micro;M. A afinidade por GA foi maior que a verificada para ATP e em ordem crescente para LbHsp90, LbHsp90_NM e LbHsp90_N. A LbHsp90 apresentou grande atividade chaperona em relação à citrato sintase, de maneira independente de ATP. A LbHsp90 mostrou baixa atividade ATPásica, a qual foi inibida pela GA com IC50 de 0,7 &micro;M. Tanto a Lbp23A quanto a Lbp23B inibiram a atividade ATPásica da LbHsp90, porém a Lbp23A aproximou-se de 100% de inibição e a Lbp23B apenas 30%. A interação in vitro entre a LbHsp90 e a Lbp23B foi observada por pull-down na presença/ausência de nucleotídeos e essa técnica não se mostrou adequada para a Lbp23A.O pioneirismo do trabalho com a Hsp90/p23 de L. braziliensis oferece uma grande contribuição para futuros trabalhos que visam o entendimento das relações funcionais entre essas proteínas e o contexto das Hsp90 no desenvolvimento da leishmaniose. / Molecular chaperones are proteins involved in proper folding of other proteins, and others important cellular functions, why they have been targeted for combating various diseases. The Hsp90 (82-96 kDa) are ubiquitous chaperones that interact with a wide range of client proteins. They are formed by three domains: N-terminal, central or middle (M), and C-terminal, which is responsible by its dimerization. The Hsp90 activity is related to its ATPase activity. During the Hsp90 functional cycle, diverse co-chaperones. One of them is the p23 (18 kDa), that interacts with one Hsp90 dimer, and some p23 functions are the inhibition of Hsp90 ATPase activity and chaperone activity. The aim of this work was obtain the Hsp90 recombinant Leishmania braziliensis Hsp90, the N and N+M domains, to determine the important factors related to conformational changes and Hsp90 function, and the molecular basis of GA inhibition. Also, to obtain the Lbp23A and Lbp23B co-chaperones in order to establish relevant aspects for LbHsp90 interaction and its co-chaperones functions. The recombinant proteins were produced, purified and characterized by biophysics techniques. The LbHsp90 was identified as an asymmetric dimer for whereas the others were identified as asymmetric monomers. The interactions between LbHsp90 and domains with nucleotides were determined by fluorescence and the dissociation constants were about 150 &micro;M. The GA-affinity was greater than ATP one, in increasing order for LbHsp90, LbHsp90_NM, and LbHsp90_N. The LbHsp90 showed large chaperone activity related to citrate synthase independently of ATP. The LbHsp90 presented low ATPase activity, which was inhibited by GA with a IC50 of 0,7. The Lbp23A and Lbp23B inhibited the ATPase activity with different values, the Lbp23A inhibition was closed to 100% whereas the Lbp23B one was 30%. The in vitro interaction between the LbHsp90 and Lbp23B was observed by pull-down, in the absence or presence of nucleotides, and for Lbp23A this technique was not appropriated. The pioneering work with Hsp90/p23 from L. braziliensis offers an important contribution to future studies aimed at understanding the functional relationships between these proteins and the context of Hsp90 in the development of leishmaniasis.