A thesis submitted to the Faculty of Science University of the Witwatersrand Johannesburg in fulfillment for the requirements of the degree of Master of Science. 14 May 2015. / Peptidomimetic compounds have been shown to exhibit both anti-HIV and anti-malarial activity. A multicomponent reaction was used to create a library of peptidomimetic compounds with an α-hydroxy-β-amino acid unit. The Passerini reaction between an aldehyde, carboxylic acid and isocyanide was used to prepare compounds containing both ester and amide functionalities. These compounds were then subjected to a deprotection-acyl migration strategy giving rise to the target compounds. This approach, known as the Passerini Amine Deprotection Acyl Migration (PADAM) sequence was successfully used to create a library of novel peptidomimetic compounds. From this library, 22 compounds were tested for activity against HIV and malaria. The Passerini reaction gives rise to a product containing a new stereogenic centre, and as the starting aldehyde used (N-Boc-phenylalaninal) has a stereogenic centre, the products were isolated as a mixture of diastereomers. Our research was also focused on finding ways of influencing the stereoselectivity of the reaction and the separation of the resulting diastereomers. The diastereomeric ratio of the Passerini products was found to be approximately 2:1 for all the reactions performed. This ratio could be modified slightly when using certain carboxylic acids and isocyanides that were either very bulky or had a stereogenic centre. Attempts to enzymatically resolve the diastereomeric products were not successful after trials using a library of 25 lipase enzymes. However, use of preparative HPLC enabled the successful separation of most of the diastereomeric mixtures, affording compounds with high purity. X-ray crystallography enabled us to identify the major diastereomers as having the R,S configuration, whilst the minor diastereomers had the S,S configuration at the two stereogenic centres. A possible explanation for the observed stereoselectivity is based on the Felkin-Anh chelation control model. It suggests that mono-protected amino aldehydes follow a chelation controlled mechanism in nucleophilic addition reactions. Chelation occurs, albeit in the form of hydrogen bonding, between the NH and carbonyl oxygen. The library of compounds was tested for activity against both HIV-1 and malaria. Only three compounds showed moderate activity against the malaria parasite, inhibiting parasitic growth by 37-42% at 5 μM respectively. Significantly, all of the active compounds contained an adamantyl moiety. Unfortunately no anti-HIV activity was seen for any of the compounds tested in the HIV-assay.

Esta tese é composta de estudos realizados com a finalidade de encontrar condições experimentais e gerar informações confiáveis que possam ser utilizadas em síntese de peptídeos mediada por lipases. Inicialmente, foram caracterizadas por eletroforese do tipo PAGE-SDS e medida de atividade em óleo de oliva duas lipases purificadas de Candida cylindracea (CCL) e duas pancreáticas suínas, purificada (pPPL) e bruta (cPPL). As CCLs apresentaram atividades lipásicas e graus de purezas superiores às PPLs. Dentre os contaminantes das PPLs, foram identificadas a tripsina e a α-quimotripsina (α-QT). Em seguida, foi realizado um estudo sistemático da síntese do dipeptídeo modelo Ac-Tyr-Gly-NH2. A melhor condição experimental encontrada foi: mistura de n-hexano/tampão Tris-HCl, 0,5M, pH 8,0, (80/20,v/v), 50mg/mL de cPPL, 0,05M de Ac-Tyr-OEt, 0,5M de Gly¬NH2, 37°C e agitação de 300 rpm, que forneceu rendimento de ~90 % em 5 min de reação. Porém, nesta condição foi observada a hidrólise secundária do produto formado, a qual foi extinta pelo tratamento da cPPL com um inibidor específico de α-QT. A condição otimizada de síntese de Ac-Tyr-Gly-NH2 também se mostrou adequada à preparação de Z¬Asp-Gly-NH2 a partir de Z-Asp-OMe e de Gly-NH2. Quando se estudou a influência da percentagem de n-hexano na eficiência da formação de ligação peptídica, ela também foi a melhor condição. Tendo escolhido a lipase e o meio reacional, iniciou-se um estudo sistemático da hidrólise do éster de onze Z-aminoácidos-OMe, o qual visou gerar informações que possibilitassem prever quais aminoácidos deveriam compor o doador de acila esterificado a ser empregado em síntese de peptídeos catalisada por cPPL. A ordem de preferência desta preparação enzimática na hidrólise de ésteres dos Z-aminoácidos-OMe testados foi a seguinte: (Lys, Arg e His)>(Phe e Tyr)>(Asp, Glu, Gln, Ser, Thr e Leu). Também foi estudada a influência da natureza do éster e do protetor de grupo α-amino na hidrólise de ésteres de Nα-acil-Asp ou -Glu. A cPPL preferiu hidrolisar o éster benzílico de Z ou Boc-Asp e de Z-Glu. Em algumas incubações para a hidrólise do éster de Z-aminoácidos-OMe foi observada uma reação secundária com possível aplicação na química de peptídeos: a remoção do grupo Z com formação do aminoácido livre correspondente. Esta ocorreu mesmo quando a tripsina e a α-QT foram inibidas irreversivelmente. Assim, Z-aminoácidos foram incubados com a cPPL e os resultados obtidos demonstraram que ela foi capaz de remover o grupo Z de onze deles com velocidades iniciais que obedecem a seguinte ordem: Tyr>Phe>Ser>Gln>Lys>His>Trp>Leu>Met>Arg>Ile. A remoção em questão também foi observada quando o dipeptídeo Z-Gly-Phe foi incubado em presença de cPPL. A formação de glicina no meio reacional decorreu da hidrólise da ligação peptídica. Sumarizando, as contribuições mais relevantes deste trabalho são: 1) a proposição inédita de um sistema bifásico para a formação da ligação peptídica catalisada por cPPL; 2) a demonstração inequívoca da presença de tripsina e α-QT e a sugestão de contaminação por carboxipeptidase A na cPPL. Estes contaminantes podem contribuir para a eficiência das sínteses de peptídeos catalisadas por esta preparação enzimática; 3) a constatação de que apesar de mais impura, a cPPL catalisou mais eficientemente do que as CCLs a formação de ligação peptídica via aminólise de ésteres; 4) a obtenção de resultados de um estudo sistemático de hidrólise de ésteres de Z-aminoácidos que podem auxiliar na escolha de doadores de acila a serem usados em sínteses de peptídeos catalisadas por cPPL; 5) a observação inédita de remoção do grupo Z de alguns Z-aminoácidos em presença de cPPL que indicou a possibilidade de novas aplicações desta preparação enzimática em química de peptídeos e, provavelmente, em síntese orgânica. / This work aimed to determine experimental conditions and reliable information to be used in peptide synthesis mediated by lipases. Thus, two Candida cylindracea lipases (CCL) and two porcine pancreatic lipases, a purified (pPPL) and a crude (cPPL), were characterized by PAGE-SDS electrophoresis and activity in olive oil. CCLs presented higher purities and enzymatic activities than PPLs. Trypsin (T) and α-chymotrypsin (α¬CT) were identified among the cPPL contaminants. A systematic investigation of Ac-Tyr¬Gly-NH2 was then performed using the CCLs, the PPLs and several experimental conditions. The best combination was: 0.05M Ac-Tyr-OEt, 0.5M Gly-NH2, 50mg/mL cPPL, mixture of n-hexane/Tris-HCl buffer 0.5M, pH 8.0, (80/20,v/v), temperature of 37176;C, shaking at 300 rpm (yield near 90% in 5 min of reaction). As secondary hydrolysis occurred in long-lasting reactions, cPPL was treated with the irreversible inhibitor of α-CT and had the amidase activity extinguished. The optimized synthesis conditions were also suitable for the preparation of Z-Asp-Gly-NH2. When the effect of the n-hexane content on coupling efficiency was examined, those were confirmed as the best conditions to be used. A further systematic investigation aiming to determine which esterified Nα-acyl-amino acids are good substrates for cPPL was then conducted using Z-amino acids-OMe. The results obtained in the monitoring of the ester hydrolysis indicated the following preference: (Z-Lys-OMe, -Arg-, -His-)>(Z-Phe-OMe, Tyr-)>(Z-Asp-OMe, -Glu-, -Gln-, ¬Ser-, -Thr-, Leu-). The natures of the ester and N-protecting group influenced the ester hydrolyses of Nα-acyl-Asp and Glu. The best substrates were Z or Boc-Asp-OBzl and Z-Glu-OBzl. Surprisingly, Z-group removal occurred in a few ester hydrolysis reactions since the resulting Z-amino acids were consumed and the corresponding free amino acids were formed. This unexpected reaction was not avoided when cPPL was treated with irreversible inhibitors of T or of α-QT. Incubation of cPPL with 11 of the 20 Z-amino acids tested gave Z-group removal initial rates that followed the order: Tyr>Phe>Ser>Gln>Lys>His>Trp>Leu>Met>Arg>Ile. In the presence of cPPL the Z-group was also removed from the dipeptide Z-Gly-Phe. Interestingly, free Gly was also detected in the reaction medium. In summary, the most relevant contributions of the present work are: 1) the proposal of a biphasic solvent system suitable for peptide bond formation catalyzed by cPPL; 2) the unequivocal demonstration that T and α-QT are contaminants of cPPL and the suggestion that carboxypeptidase A can also be present in it (all of them may interfere in the efficiency of peptide formation catalyzed by cPPL); 3) the verification that, although impure, cPPL catalyzed dipeptide synthesis more efficiently than the CCLs; 4) the performance of the first systematic study of ester hydrolysis of Z-amino acids catalyzed by cPPL; 5) the observation of Z group removal during some Z-amino acid ester hydrolyses catalyzed by cPPL and the confirmation that this is also feasible for some Z¬amino acids and a Z-dipeptide.

A utilização de antígenos de Taenia crassiceps vem se mostrando como via alternativa no imunodiagnóstico da neurocisticercose (NC), sendo as frações de 18 e 14 kDa consideradas específicas. No presente trabalho, foram sintetizados seis peptídeos, com base nas seqüências de aminoácidos das proteínas de 10, 14 e 18 kDa de T. crassiceps e homólogas às seqüências de aminoácidos de T. solium. Os peptídeos foram divididos em \"a\" e \"b\", denominados como, P1a, P2a, P3a e P4a e P1b, P3b e P4b, sendo, as seqüências de aminoácidos dos peptídeos \"a\", uma seqüência interna dos peptídeos \"b\". Em estudo da antigenicidade dos peptídeos conduzido por teste ELISA, P1a e P4a isolados ou utilizados como múltiplos peptídeos antigênicos (MAP) contendo dois, três ou quatro peptídeos, apresentaram reatividade com soro hiperimune anti-líquido vesicular de T. crassiceps, enquanto que MAPs contendo apenas P2a e P3a não foram antigênicos. Anticorpos monoclonais (AcMos) anti-T. crassiceps (n=3) e anti-T. solium (n=19), reconheceram, em ordem decrescente, P1b (72,7%), P1a (45,5%) e P3a e P2a (9,1%), enquanto que P3b, P4a e P4b não apresentaram reatividade com os AcMos utilizados. Com soros humanos de pacientes com NC (NC) e de indivíduos supostamente saudáveis (ISS), P1b e P1a foram considerados potencialmente antigênicos, isolados ou em MAPs com três ou quatro peptídeos. A avaliação do teste ELISA com peptídeo sintético isolado ou MAP, respectivamente, P1b e MAP-a (P1a+P3a+P4a), foi realizada baseando-se em três diferentes cut off, a, b e TG-ROC. De acordo com os cut off utilizados, ELISA com P1b apresentou índices de positividade entre 59,0-79,5% com amostras de soros NC (n=39); 1,3-11,8% com ISS (n=76); 3,4-10,2% com amostras de soros de pacientes com hidatidose provindos do Rio Grande do Sul (H-R) (n=59); 0,0-50,0% com amostras de soros de pacientes com hidatidose provindos do Peru (H-P) (n=8) e 0,0-9,1% com amostras de soros de pacientes com outras parasitoses (OP) (n=33). ELISA com MAP-a apresentou índices de positividade entre 57,7-92,3% com NC (n=26); 1,4-9,6% com ISS (n=73); 0,0-13,3% com H-R (n=15) e 12,5-37,5% com H-P (n=8). Na tentativa de aumentar a positividade do teste ELISA com peptídeos sintéticos, antígeno de 18 e14 kDa de T. crassiceps foi adicionado, porém, não houve maior antigenicidade ao complexo antigênico. Os peptídeos sintéticos utilizados mostraram-se promissores para o diagnóstico sorológico da NC, porém, não foram representativos dos epítopos imunodominantes presentes em cisticercos de T. solium. Outras seqüências de aminoácidos necessitam ser ensaiadas, a fim de obter um complexo antigênico sintético equivalente ao antígeno nativo, porém, o alto custo da síntese dos peptídeos ainda é uma barreira que limita a investigação de novos MAPs. / Taenia crassiceps antigens have been showed like one alternative rote to the immunodiagnosis of neurocysticercosis (NC), where 18- and 14-kDa fractions have been considered specific. In this study, six peptides were synthesized based on 10, 14 and 18 kDa fractions of amino acids sequence of proteins of the T.crassiceps and homologous to T. solium. Peptides were divided in \"a\" and \"b\", denominated P1a, P2a, P3a and P4a and P1b, P3b and P4b, being that amino acids sequences of the \"a\" peptides are one internal sequence of the \"b\" peptides. In antigenic study of the peptides conducted by ELISA, isolated P1a and P4a peptides or used like multiple antigenic peptides (MAP) with two, three or four peptides, cross-reacted with anti-vesicular fluid of the T. crassiceps hyperimmune serum, while that, MAPs with only P2a and P3a did not showed antigenicity. Monoclonal antibodies (Mabs) anti-T. crassiceps (n=3) and anti-T.solium (n=19) Mabs recognized in decreasing order, P1b (72,7%), P1a (45,5%) and P3a and P2a (9,1%), while, P3b, P4a and P4b did not showed reactivity with Mabs used. In human serum samples of the patients with neurocysticercosis (NC) and serum healthy individuals (HI), where P1b and P1a peptides were analyzed isolated or in MAPs with three or four peptides, both of them showed antigenic potential. The evaluation of the ELISA tests with synthetic peptides isolated or in MAPs, P1b and MAP-a (P1a+P3a+P4a), respectively, was analyzed in three differents cut off, a, b and TG-Roc. Based on its, ELISA assayed with P1b showed 59,0-79,5% positivity when NC serum samples where tested (n=39); 1,3-11,8% with HI serum samples (n=76); 3,4-10,2% with human serum samples of the patients with hydatidosis from Rio Grande do Sul (H-R) (n=59); 0,0-50,0% with human serum samples of the patients with hydatidosis from Peru (H-P) (n=8) and 0,0-9,1% with human serum samples of the patients with others parasitoses (OP) (n=33). By the way, ELISA assayed with MAP-a showed 57,7-92,3% positivity with NC (n=26); 1,4-9,6% with HI (n=73); 0,0-13,3% with H-R (n=15) and 12,5-37,5% with H-P (n=8). On the attempt of increase the positivity of the ELISA test using synthetic peptides, 18- and 14-kDa fractions of the T. crassiceps was added, but they did not promoted more antigenicity. Synthetic peptides used showed promising results on neurocysticercosis serumdiagnosis, but they were no representatives of dominants epitopes present in T. solium cysticercus. Others amino acids sequences need be used to have a synthetic antigenic complex similar to native antigens, however, the high cost of the peptide synthesis still is a problem that limit the study of the news MAPs.

Biomimetic peptides are autonomously folding secondary structural units designed to serve as models for examining processes that occur in proteins. Although de novo biomimetic peptides are not simply abbreviated versions of proteins already found in nature, designing biomimetic peptides does require an understanding of how native proteins are formed and stabilized. The discovery of autonomously folding fragments of ribonuclease A and tendamistat pioneered the use of biomimetic peptides for determining how the polypeptide sequence stabilizes formation of alpha helices and beta hairpins in aqueous and organic solutions. A set of rules for constructing stable alpha helices have now been established. There is no exact set of rules for designing beta hairpins; however, some factors that must be considered are the identity of the residues in the turn and non-covalent interactions between amino acid side chains. For example, glycine, proline, aspargine, and aspartic acid are favored in turns. Non-covalent interactions that stabilize hairpin formation include salt bridges, pi-stacked aromatic interactions, cation-pi interactions, and hydrophobic interactions. The optimal strand length for beta hairpins depends on the numbers of stabilizing non-covalent interactions and high hairpin propensity amino acids in the specific peptide being designed. Until now, de novo hairpins have not previously been used to examine biological processes aside from protein folding. This thesis uses de novo designed biomimetic peptides as tractable models to examine how non-covalent interactions control the redox properties of tyrosine in enzymes. The data in this study demonstrate that proton transfer to histidine, a hydrogen bond to arginine, and a pi-cation interaction create a peptide environment that lowers the midpoint potential of tyrosine in beta hairpins. Moreover, these interactions contribute equally to control the midpoint potential. The data also show that hydrogen bonding is not the sole determinant of the midpoint potential of tyrosine. Finally, the data suggest that the Tyr 160D2-Arg 272CP47 pi-cation interaction contributes to the differences in redox properties between Tyr 160 and Tyr 161 of photosystem II.

Copies of author's previously published articles inserted. / Bibliography: leaves 89-126. / vii, 126, [88] leaves, [1] leaf of plates : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Finds that the metabolism of substance P (SP) and the subsequent production of SP-(7-11) is important in regulating the biological activity of SP on chondrycytes in the synoviol joint. / Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, 1996?

Cyclic peptides possess desirable characteristics as potential pharmaceutical scaffolds. The cyanobactin family of cyclic peptide natural products boast diverse structures and bioactivity. Exemplars are the patellamides, which have attracted attention due to their ability to reverse the effects of multi-drug resistance in human leukemia cells. In addition to their macrocyclic architecture patellamides contain azol(in)e heterocycles and d-amino acids. This structural complexity makes them challenging targets for chemical synthesis. Understanding their biosynthesis will enable the development of a biotechnological ‘toolkit' for the synthesis of new pharmaceutical compounds. Patellamides are ribosomally-synthesised and post-translationally modified peptides (RiPPs) and much of their biosynthesis has been elucidated, however there are still elements of their biosynthesis that are not yet fully understood. PatA and PatG contain C-terminal domains of unknown function (DUFs). The crystal structure of PatG-DUF has been solved and subsequent to biochemical and biophysical investigation PatG-DUF was found not to constitute an essential part of the biotechnological ‘toolkit' and can be excluded from in vitro enzyme-based synthesis of cyanobactin-like cyclic peptides. The cyanobactin heterocyclases are able to introduce heterocycles into a peptide backbone, seemingly irrespective of the neighbouring residues; however a molecular rational governing substrate recognition is unknown. Additionally the mechanism of heterocyclisaton is disputed. Analysis of crystal structures of LynD in complex with cofactor and substrate (solved by Dr Jesko Koehnke) enabled the active site and substrate recognition site to be located. A new mechanism for heterocyclisation has been proposed. Guided by the substrate recognition observed in complex structures a constituently active heterocyclase (AcLynD) has been engineered, which is able to process short, leaderless peptide substrates. Epimerisation in cyanobactin biosynthesis is believed to be spontaneous, but its precise timing is uncertain. NMR analysis of selectively labelled peptide substrates processed by the modifying enzymes, identified epimerisation to be spontaneous on the macrocycle, regardless of whether the neighbouring heterocycles have been oxidised. A one-pot in vitro synthesis of cyanobactins has been developed, and employed to create a number of patellamide D analogues to ascertain structural-activity relationships.

Made available in DSpace on 2015-07-22T20:50:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-03-26. Added 1 bitstream(s) on 2015-08-11T03:25:45Z : No. of bitstreams: 1 Publico-10806.pdf: 1743333 bytes, checksum: 379793d92e9d86096d10c579b33c757e (MD5) / A hormônio protéico produzido pelo gene-ob e denominado leptina, é um produto originário do tecido adiposo, circula pelo plasma e afeta o balanço energético interagindo em receptores presentes no hipotálamo. A leptina desempenha um papel importante na regulação de uma variedade de funções fisiológicas, incluindo controle de ingestão alimentar, temperatura corporal e manutenção do peso corporal. A ausência ou resistência a leptina pelo organismo causa obesidade mórbida, diabetes e hipogonadismo. A estrutura terciária da molécula da leptina revela a presença de quatro hélices, cujo padrão é típico das citocinas. Com o objetivo de identificar a região da molécula responsável pela expressão de sua atividade biológica foram sintetizados seis fragmentos peptídicos cujas estruturas foram escolhidas de acordo com a estrutura tridimensional da leptina. Em estudos anteriores do nosso grupo, dois peptídeos, AchLEP92- 115-NH2 (IV) e Ac-[Ser117]-hLEP116-140-NH2 (V), foram reconhecidos pelo receptor da leptina presentes em células HP-75, confirmando outros trabalhos da literatura que também apontavam que é nesta região da molécula que deve estar presente o epitopo funcional da leptina. Neste trabalho, uma nova série de fragmentos, cujas estruturas primárias estão contidas na região dos fragmentos IV e V, foram sintetizados e os efeitos dos mesmos na variação do peso corporal e no consumo de alimento quando administrados no ventrículo cerebral de ratos normais foram avaliados. Os peptídeos foram sintetizados pelo método da fase sólida manual pela estratégia t-Boc. Os mesmos foram purificados por cromatografia liquida de alta eficiência e foram caracterizados por análise de aminoácidos e cromatografia liquida acoplada a um espectrômetro de massas. Estudos conformacionais dos peptídeos também foram realizados por Dicroísmo Circular com o objetivo de correlacionar a estrutura com a atividade biológica dos fragmentos. Dentre os compostos estudados, o melhor resultado foi obtido com o fragmento AchLEP110- 119-NH2 (VI) que se mostrou ser mais ativo que a própia leptina e foi equipotente com o [D-Leu4]-OB3, que até então era o fragmento mais ativo descrito na literatura. Embora haja a necessidade de refinamentos, esse tipo de abordagem pode oferecer uma interessante base para o desenvolvimento de compostos correlacionados com a leptina com potencial de aplicação em estudos de obesidade humana ou na medicina veterinária. / The protein hormone produced by the ob-gene and denominated leptin, a product originating from adipose tissue, circulates in the plasma and affects the energy balance by interacting with the hypothalamus. Leptin plays an important role in the regulation of a variety of physiological functions, including food intake, body temperature and body weight maintenance. Total absence or resistance to leptin causes morbid obesity, diabetes and hypogonadism. The tertiary structure of the leptin molecule reveals the existence of a fourhelix bundle that is characteristic of the short-helix cytokines. To identify regions of the leptin molecule responsible for its bioactivity, we have synthesized six peptides based on the protein three-dimensional structure. Our results indicated that the fragments AchLEP92- 115-NH2 (IV) and Ac-[Ser117]-hLEP116-140-NH2 (V) were recognized by leptin receptor present in hp-75 cells, in agreement with the obtained by other authors, validating that this region of the molecule contain the functional epitope of the leptin molecule. In the present study, a new series of peptides encompassing the region of fragments IV and V of leptin were synthesized, and their effects on body weight and food intake were assessed when administered into the lateral cerebroventricle of normal rats. Peptides were synthesized by the solid phase methodology, purified by RP-HPLC and characterized by LC/ESI-MS. We also performed a conformational study of the peptides by circular dichroism in order to correlate the biological activity and secondary structure of the leptin fragments. Out off the new series of compounds, the best results were obtained with the fragment Ac-hLEP110-119-NH2 (VI) which showed to be more active than leptin and equipotent to [D-Leu4]-OB3 the most active leptin fragment described in the literature so far. Although the peptide fragments design needs refinement, this kind of approach may offer the basis for the development of leptin-related compounds with potential application in human obesity or veterinary medicine. / TEDE / BV UNIFESP: Teses e dissertações

Cyclic peptides have potential as scaffolds for novel pharmaceuticals, however their chemical synthesis can be challenging and as such natural sources are often explored. Several species of cyanobacteria produce a family of cyclic peptides, the cyanobactins, through the ribosomal synthesis of precursor peptides and post-translational tailoring. The patellamides, a member of the cyanobactin family, are cyclic octapeptides containing D-stereo centres and heterocyclised amino acids. A single gene cluster, patA - patG, contains the genes for the expression of the precursor peptide and the enzymes responsible for post-translational modifications including a heterocyclase, protease, macrocyclase and oxidase. Biochemical and structural analysis on the patellamide and related cyanobactin pathways has been carried out. The crystal structure of PatF, a proposed prenyl transferase, has been determined, highlighting that it is likely evolutionary inactive due to changes to key residues when compared to active homologues. This is in agreement with the knowledge that no naturally prenylated patellamides have been discovered to date. The crystal structure of the macrocyclase domain of PatG has been determined in complex with a substrate analogue peptide. The structure, together with biochemical analysis has allowed a mechanism of macrocyclisation to be proposed, confirming the requirement of a specific substrate conformation to enable macrocyclisation. Using isolated enzymes from the patellamide and related pathways, a small scale library of macrocycles made up of diverse sequences has been created in vitro and characterised by mass spectrometry and in certain cases NMR. In order to further enhance diversity, macrocycles containing unnatural amino acids have been created using three approaches; SeCys derived precursor peptides, intein-mediated peptide ligation and pEVOL amber codon technology. Finally, two oxidase enzymes from cyanobactin pathways have been purified, characterised and confirmed active for thiazoline oxidation. Native X-ray datasets on crystals of the oxidase CyaGox have been collected and phasing trials are on-going.

Esta tese é composta de estudos realizados com a finalidade de encontrar condições experimentais e gerar informações confiáveis que possam ser utilizadas em síntese de peptídeos mediada por lipases. Inicialmente, foram caracterizadas por eletroforese do tipo PAGE-SDS e medida de atividade em óleo de oliva duas lipases purificadas de Candida cylindracea (CCL) e duas pancreáticas suínas, purificada (pPPL) e bruta (cPPL). As CCLs apresentaram atividades lipásicas e graus de purezas superiores às PPLs. Dentre os contaminantes das PPLs, foram identificadas a tripsina e a α-quimotripsina (α-QT). Em seguida, foi realizado um estudo sistemático da síntese do dipeptídeo modelo Ac-Tyr-Gly-NH2. A melhor condição experimental encontrada foi: mistura de n-hexano/tampão Tris-HCl, 0,5M, pH 8,0, (80/20,v/v), 50mg/mL de cPPL, 0,05M de Ac-Tyr-OEt, 0,5M de Gly¬NH2, 37°C e agitação de 300 rpm, que forneceu rendimento de ~90 % em 5 min de reação. Porém, nesta condição foi observada a hidrólise secundária do produto formado, a qual foi extinta pelo tratamento da cPPL com um inibidor específico de α-QT. A condição otimizada de síntese de Ac-Tyr-Gly-NH2 também se mostrou adequada à preparação de Z¬Asp-Gly-NH2 a partir de Z-Asp-OMe e de Gly-NH2. Quando se estudou a influência da percentagem de n-hexano na eficiência da formação de ligação peptídica, ela também foi a melhor condição. Tendo escolhido a lipase e o meio reacional, iniciou-se um estudo sistemático da hidrólise do éster de onze Z-aminoácidos-OMe, o qual visou gerar informações que possibilitassem prever quais aminoácidos deveriam compor o doador de acila esterificado a ser empregado em síntese de peptídeos catalisada por cPPL. A ordem de preferência desta preparação enzimática na hidrólise de ésteres dos Z-aminoácidos-OMe testados foi a seguinte: (Lys, Arg e His)>(Phe e Tyr)>(Asp, Glu, Gln, Ser, Thr e Leu). Também foi estudada a influência da natureza do éster e do protetor de grupo α-amino na hidrólise de ésteres de Nα-acil-Asp ou -Glu. A cPPL preferiu hidrolisar o éster benzílico de Z ou Boc-Asp e de Z-Glu. Em algumas incubações para a hidrólise do éster de Z-aminoácidos-OMe foi observada uma reação secundária com possível aplicação na química de peptídeos: a remoção do grupo Z com formação do aminoácido livre correspondente. Esta ocorreu mesmo quando a tripsina e a α-QT foram inibidas irreversivelmente. Assim, Z-aminoácidos foram incubados com a cPPL e os resultados obtidos demonstraram que ela foi capaz de remover o grupo Z de onze deles com velocidades iniciais que obedecem a seguinte ordem: Tyr>Phe>Ser>Gln>Lys>His>Trp>Leu>Met>Arg>Ile. A remoção em questão também foi observada quando o dipeptídeo Z-Gly-Phe foi incubado em presença de cPPL. A formação de glicina no meio reacional decorreu da hidrólise da ligação peptídica. Sumarizando, as contribuições mais relevantes deste trabalho são: 1) a proposição inédita de um sistema bifásico para a formação da ligação peptídica catalisada por cPPL; 2) a demonstração inequívoca da presença de tripsina e α-QT e a sugestão de contaminação por carboxipeptidase A na cPPL. Estes contaminantes podem contribuir para a eficiência das sínteses de peptídeos catalisadas por esta preparação enzimática; 3) a constatação de que apesar de mais impura, a cPPL catalisou mais eficientemente do que as CCLs a formação de ligação peptídica via aminólise de ésteres; 4) a obtenção de resultados de um estudo sistemático de hidrólise de ésteres de Z-aminoácidos que podem auxiliar na escolha de doadores de acila a serem usados em sínteses de peptídeos catalisadas por cPPL; 5) a observação inédita de remoção do grupo Z de alguns Z-aminoácidos em presença de cPPL que indicou a possibilidade de novas aplicações desta preparação enzimática em química de peptídeos e, provavelmente, em síntese orgânica. / This work aimed to determine experimental conditions and reliable information to be used in peptide synthesis mediated by lipases. Thus, two Candida cylindracea lipases (CCL) and two porcine pancreatic lipases, a purified (pPPL) and a crude (cPPL), were characterized by PAGE-SDS electrophoresis and activity in olive oil. CCLs presented higher purities and enzymatic activities than PPLs. Trypsin (T) and α-chymotrypsin (α¬CT) were identified among the cPPL contaminants. A systematic investigation of Ac-Tyr¬Gly-NH2 was then performed using the CCLs, the PPLs and several experimental conditions. The best combination was: 0.05M Ac-Tyr-OEt, 0.5M Gly-NH2, 50mg/mL cPPL, mixture of n-hexane/Tris-HCl buffer 0.5M, pH 8.0, (80/20,v/v), temperature of 37176;C, shaking at 300 rpm (yield near 90% in 5 min of reaction). As secondary hydrolysis occurred in long-lasting reactions, cPPL was treated with the irreversible inhibitor of α-CT and had the amidase activity extinguished. The optimized synthesis conditions were also suitable for the preparation of Z-Asp-Gly-NH2. When the effect of the n-hexane content on coupling efficiency was examined, those were confirmed as the best conditions to be used. A further systematic investigation aiming to determine which esterified Nα-acyl-amino acids are good substrates for cPPL was then conducted using Z-amino acids-OMe. The results obtained in the monitoring of the ester hydrolysis indicated the following preference: (Z-Lys-OMe, -Arg-, -His-)>(Z-Phe-OMe, Tyr-)>(Z-Asp-OMe, -Glu-, -Gln-, ¬Ser-, -Thr-, Leu-). The natures of the ester and N-protecting group influenced the ester hydrolyses of Nα-acyl-Asp and Glu. The best substrates were Z or Boc-Asp-OBzl and Z-Glu-OBzl. Surprisingly, Z-group removal occurred in a few ester hydrolysis reactions since the resulting Z-amino acids were consumed and the corresponding free amino acids were formed. This unexpected reaction was not avoided when cPPL was treated with irreversible inhibitors of T or of α-QT. Incubation of cPPL with 11 of the 20 Z-amino acids tested gave Z-group removal initial rates that followed the order: Tyr>Phe>Ser>Gln>Lys>His>Trp>Leu>Met>Arg>Ile. In the presence of cPPL the Z-group was also removed from the dipeptide Z-Gly-Phe. Interestingly, free Gly was also detected in the reaction medium. In summary, the most relevant contributions of the present work are: 1) the proposal of a biphasic solvent system suitable for peptide bond formation catalyzed by cPPL; 2) the unequivocal demonstration that T and α-QT are contaminants of cPPL and the suggestion that carboxypeptidase A can also be present in it (all of them may interfere in the efficiency of peptide formation catalyzed by cPPL); 3) the verification that, although impure, cPPL catalyzed dipeptide synthesis more efficiently than the CCLs; 4) the performance of the first systematic study of ester hydrolysis of Z-amino acids catalyzed by cPPL; 5) the observation of Z group removal during some Z-amino acid ester hydrolyses catalyzed by cPPL and the confirmation that this is also feasible for some Z¬amino acids and a Z-dipeptide.

A utilização de antígenos de Taenia crassiceps vem se mostrando como via alternativa no imunodiagnóstico da neurocisticercose (NC), sendo as frações de 18 e 14 kDa consideradas específicas. No presente trabalho, foram sintetizados seis peptídeos, com base nas seqüências de aminoácidos das proteínas de 10, 14 e 18 kDa de T. crassiceps e homólogas às seqüências de aminoácidos de T. solium. Os peptídeos foram divididos em \"a\" e \"b\", denominados como, P1a, P2a, P3a e P4a e P1b, P3b e P4b, sendo, as seqüências de aminoácidos dos peptídeos \"a\", uma seqüência interna dos peptídeos \"b\". Em estudo da antigenicidade dos peptídeos conduzido por teste ELISA, P1a e P4a isolados ou utilizados como múltiplos peptídeos antigênicos (MAP) contendo dois, três ou quatro peptídeos, apresentaram reatividade com soro hiperimune anti-líquido vesicular de T. crassiceps, enquanto que MAPs contendo apenas P2a e P3a não foram antigênicos. Anticorpos monoclonais (AcMos) anti-T. crassiceps (n=3) e anti-T. solium (n=19), reconheceram, em ordem decrescente, P1b (72,7%), P1a (45,5%) e P3a e P2a (9,1%), enquanto que P3b, P4a e P4b não apresentaram reatividade com os AcMos utilizados. Com soros humanos de pacientes com NC (NC) e de indivíduos supostamente saudáveis (ISS), P1b e P1a foram considerados potencialmente antigênicos, isolados ou em MAPs com três ou quatro peptídeos. A avaliação do teste ELISA com peptídeo sintético isolado ou MAP, respectivamente, P1b e MAP-a (P1a+P3a+P4a), foi realizada baseando-se em três diferentes cut off, a, b e TG-ROC. De acordo com os cut off utilizados, ELISA com P1b apresentou índices de positividade entre 59,0-79,5% com amostras de soros NC (n=39); 1,3-11,8% com ISS (n=76); 3,4-10,2% com amostras de soros de pacientes com hidatidose provindos do Rio Grande do Sul (H-R) (n=59); 0,0-50,0% com amostras de soros de pacientes com hidatidose provindos do Peru (H-P) (n=8) e 0,0-9,1% com amostras de soros de pacientes com outras parasitoses (OP) (n=33). ELISA com MAP-a apresentou índices de positividade entre 57,7-92,3% com NC (n=26); 1,4-9,6% com ISS (n=73); 0,0-13,3% com H-R (n=15) e 12,5-37,5% com H-P (n=8). Na tentativa de aumentar a positividade do teste ELISA com peptídeos sintéticos, antígeno de 18 e14 kDa de T. crassiceps foi adicionado, porém, não houve maior antigenicidade ao complexo antigênico. Os peptídeos sintéticos utilizados mostraram-se promissores para o diagnóstico sorológico da NC, porém, não foram representativos dos epítopos imunodominantes presentes em cisticercos de T. solium. Outras seqüências de aminoácidos necessitam ser ensaiadas, a fim de obter um complexo antigênico sintético equivalente ao antígeno nativo, porém, o alto custo da síntese dos peptídeos ainda é uma barreira que limita a investigação de novos MAPs. / Taenia crassiceps antigens have been showed like one alternative rote to the immunodiagnosis of neurocysticercosis (NC), where 18- and 14-kDa fractions have been considered specific. In this study, six peptides were synthesized based on 10, 14 and 18 kDa fractions of amino acids sequence of proteins of the T.crassiceps and homologous to T. solium. Peptides were divided in \"a\" and \"b\", denominated P1a, P2a, P3a and P4a and P1b, P3b and P4b, being that amino acids sequences of the \"a\" peptides are one internal sequence of the \"b\" peptides. In antigenic study of the peptides conducted by ELISA, isolated P1a and P4a peptides or used like multiple antigenic peptides (MAP) with two, three or four peptides, cross-reacted with anti-vesicular fluid of the T. crassiceps hyperimmune serum, while that, MAPs with only P2a and P3a did not showed antigenicity. Monoclonal antibodies (Mabs) anti-T. crassiceps (n=3) and anti-T.solium (n=19) Mabs recognized in decreasing order, P1b (72,7%), P1a (45,5%) and P3a and P2a (9,1%), while, P3b, P4a and P4b did not showed reactivity with Mabs used. In human serum samples of the patients with neurocysticercosis (NC) and serum healthy individuals (HI), where P1b and P1a peptides were analyzed isolated or in MAPs with three or four peptides, both of them showed antigenic potential. The evaluation of the ELISA tests with synthetic peptides isolated or in MAPs, P1b and MAP-a (P1a+P3a+P4a), respectively, was analyzed in three differents cut off, a, b and TG-Roc. Based on its, ELISA assayed with P1b showed 59,0-79,5% positivity when NC serum samples where tested (n=39); 1,3-11,8% with HI serum samples (n=76); 3,4-10,2% with human serum samples of the patients with hydatidosis from Rio Grande do Sul (H-R) (n=59); 0,0-50,0% with human serum samples of the patients with hydatidosis from Peru (H-P) (n=8) and 0,0-9,1% with human serum samples of the patients with others parasitoses (OP) (n=33). By the way, ELISA assayed with MAP-a showed 57,7-92,3% positivity with NC (n=26); 1,4-9,6% with HI (n=73); 0,0-13,3% with H-R (n=15) and 12,5-37,5% with H-P (n=8). On the attempt of increase the positivity of the ELISA test using synthetic peptides, 18- and 14-kDa fractions of the T. crassiceps was added, but they did not promoted more antigenicity. Synthetic peptides used showed promising results on neurocysticercosis serumdiagnosis, but they were no representatives of dominants epitopes present in T. solium cysticercus. Others amino acids sequences need be used to have a synthetic antigenic complex similar to native antigens, however, the high cost of the peptide synthesis still is a problem that limit the study of the news MAPs.