No description available.

No description available.

No description available.

<p> Some plants such as spinach, sugar beet, and wheat accumulate the quaternary ammonium compound glycine betaine when exposed to stresses in their environment. Environmental stress can be in the form of an excess or deficiency of water, high salt content, and/or exposure to excessively low or high temperatures and many if not all of these stresses are associated with cell dehydration. </p> <p> Glycine betaine is an organic solute that is believed to help restore the osmotic potential of a cell undergoing dehydration by reducing water loss and preventing damage to the structure and function of macromolecules. However, many plants such as Arabidopsis, tobacco, and rice do not accumulate glycine betaine. Given the perceived benefits of glycine betaine production by plants under stress, studies have been carried out to identify factors regulating its production. </p> <p> Glycine betaine is synthesized by the two-step oxidation of choline. The capacity to synthesize phosphocholine for choline production has been found to limit the production of glycine betaine in non-accumulating plants such as tobacco. As such, genetic engineering has been used to enhance the production of choline to up-regulate the synthesis of glycine betaine. This strategy has required knowledge of the enzyme(s) catalyzing the three N-methylation steps of the phosphocholine biosynthetic pathway. </p> <p> This study focused on a gene product identified as putative-phosphoethanolamine N-methyltransferase (putative PEAMT) based upon its similarity to a spinach Nmethyltransferase known to convert phosphoethanolamine to phosphocholine. This gene is located at the locus Atlg73600 on chromosome I of Arabidopsis and its predicted amino acid sequence has high similarity to two other genes encoding N-methylating enzymes located at At3 g 18000 (a biochemically confirmed PEAMT) and At 1 g48600 (annotated as a putative PEAMT). </p> <p> In this study, publicly available microarray data was examined to identify an expression profile of transcripts associated with the Atlg73600 gene in organs and tissues of Arabidopsis at various developmental stages. A summary of the micro array data shows the highest abundance of transcripts for Atlg73600 to be in the rosette leaves of Arabidopsis at 18.0- 20.9 days of growth. </p> <p> Arabidopsis plants grown from seeds from four SALK lines reported to have a TDNA insert in the Atlg73600 gene were screened for the presence of a T-DNA tag using a three primer PCR design strategy. Individual plants from two of the lines were found to have a T-DNA insert present. RT-PCR was then used to analyze the expression of transcripts associated with the Atlg73600 gene in these mutant lines. Transcripts were not detected among the amplified products from eDNA produced from the SALK line designated 062703 but they were found at reduced levels in eDNA of SALK line 016929c. </p> <p> In future studies the two T -DNA mutant lines identified in this study can be used to assign a biological role for the product of the Atlg73600 gene by examining the phenotype of these mutant plants relative to that of wild-type plants under normal and/or stressed conditions. The line found with no expression associated with the Atlg73600 gene will be useful in crosses with T -DNA knock-out mutants of genes at loci At3g18000 and Atlg48600. Systematic knock-outs for each of the genes in isolation and in combination will help discern whether there is functional redundancy in their biological roles or if their individual expression contributes uniquely towards the development of a plant or its stress response. Given the associated role for PEAMT in phosphatidylcholine metabolism, lipidomics could be used to determine if the composition of the plant membranes is altered relative to wild-type when the Atlg73600 gene is knocked-out. </p> / Thesis / Master of Science (MSc)

Proteinmethylierung spielt eine immer größere Rolle in der Regulierung zellulärer Prozesse. Die Entwicklung effizienter proteomweiter Methoden zur Detektion von Methylierung auf Proteinen ist limitiert und technisch schwierig. In dieser Arbeit haben wir einen neuen Hefe-Zwei-Hybrid-Ansatz (Y2H) entwickelt, der Proteine, die miteinander wechselwirken, mit Hilfe von Sequenzierungen der zweiten Generation identifiziert (Y2H-Seq). Der neue Y2H-Seq-Ansatz wurde systematisch mit dem Y2H-Seq-Ansatz verglichen. Dafür wurde ein Bait-Set von 8 Protein-Arginin-Methyltransferasen, 17 Protein-Lysin-Methyltransferasen und 10 Demethylasen gegen 14,268 Prey-Proteine getestet. Der Y2H-Seq-Ansatz ist weniger arbeitsintensiv, hat eine höhere Sensitivität als der Standard Y2H-Matrix-Ansatz und ist deshalb besonders geeignet, um schwache Interaktionen zwischen Substraten und Protein-Methyltransferasen zu detektieren. Insgesamt wurden 523 Wechselwirkungen zwischen 22 Bait-Proteinen und 324 Prey-Pr oteinen etabliert, darunter 11 bekannte Methyltransferasen-Substrate. Netzwerkanalysen zeigen, dass Methyltransferasen bevorzugt mit Transkriptionsregulatoren, DNA- und RNA-Bindeproteinen wechselwirken. Diese Daten repräsentieren das erste proteomweite Wechselwirkungsnetzwerk über Protein-Methyltransferasen und dienen als Ressource für neue potentielle Methylierungssubstrate. In einem in vitro Methylierungsassay wurden exemplarisch mit Hilfe massenspektrometrischer Analysen die methylierten Aminosäurereste einiger Kandidatenproteine bestimmt. Von neun getesteten Proteinen waren sieben methyliert, zu denen gehören SPIN2B, DNAJA3, QKI, SAMD3, OFCC1, SYNCRIP und WDR42A. Wahrscheinlich sind viele Methylierungssubstrate im Netzwerk vorhanden. Das vorgestellte Protein-Protein-Wechselwirkungsnetzwerk zeigt, dass Proteinmethylierung sehr unterschiedliche zelluläre Prozesse beeinflusst und ermöglicht die Aufstellung neuer Hypothesen über die Regulierung Molekularer Mechanismen durch Methylierung. / Protein methylation on arginine and lysine residues is a largely unexplored posttranslational modification which regulates diverse cellular processes. The development of efficient proteome-wide approaches for detecting protein methylation is limited and technically challenging. We developed a novel workload reduced yeast-two hybrid (Y2H) approach to detect protein-protein interactions utilizing second generation sequencing. The novel Y2H-seq approach was systematically evaluated against our state of the art Y2H-matrix screening approach and used to screen 8 protein arginine methyltransferases, 17 protein lysine methyltransferases and 10 demethylases against a set of 14,268 proteins. Comparison of the two approaches revealed a higher sensitivity of the new Y2H-seq approach. The increased sampling rate of the Y2H-seq approach is advantageous when assaying transient interactions between substrates and methyltransferases. Overall 523 interactions between 22 bait proteins and 324 prey proteins were identified including 11 proteins known to be methylated. Network analysis revealed enrichment of transcription regulator activity, DNA- and RNA-binding function of proteins interacting with protein methyltransferases. The dataset represents the first proteome-wide interaction network of enzymes involved in methylation and provides a comprehensively annotated resource of potential new methylation substrates. An in vitro methylation assay coupled to mass spectrometry revealed amino acid methylation of candidate proteins. Seven of nine proteins tested were methylated including SPIN2B, DNAJA3, QKI, SAMD3, OFCC1, SYNCRIP and WDR42A indicating that the interaction network is likely to contain many putative methyltransferase substrate pairs. The presented protein-protein interaction network demonstrates that protein methylation is involved in diverse cellular processes and can inform hypothesis driven investigation into molecular mechanisms regulated through methylation.

No description available.

Les protéines arginine méthyl transférases ("PRMTs") sont impliquées dans de nombreux processus cellulaires essentiels. La protéine CARMI ("Coactivator-associated arginine methyltransferase 1", appelée aussi "PRMT4") a été initialement identifiée par sa fonction co-activatrice de la transcription impliquantplusieurs récepteurs nucléaires des hormones. CARMI est une enzyme qui catalyse la réaction de méthylation sur les histones via un donneur de méthyl naturel, la S-adénosY-L -méthionine (SAM). De nombreux travaux ont montré que CARMI est surexprimée dans les cancers du sein et de la prostate. L' objectif de ce travail est la compréhension à l'échelle moléculaire du mode d'action de CARMI et l'étude du mécanisme de reconnaissances moléculaires et de transferts d' informations gouvernés par la protéine CARMI. La structure cristallographique obtenue de cette enzyme en présence de cofacteur, la S-AdénosyhHomocystéine ou la Sinefungine a eu un effet stabilisant. Ainsi, notre stratégie a été de créer des molécules hameçons basées sur le motif de la SAM capables d' ancrer un peptide mimant la séquence de l' histone H3, pour ensuite les tester en co-cristallisation avec CARMI. Ainsi, grâce à la diffraction aux rayons X, les interactions mises en jeu dans le complexe CARMlImolécules hameçons/peptide pourront être déterminées. Cette stratégie s'est effectuée en trois étapes : la première étape, décrite dans le chapitre 2, a consisté en la synthèse d'analogues de la SAM obtenus grâce à des modifications réalisées autour de l'atome de soufre. Ces composés nous ont permis d' explorer la « poche du sulfonium ». Puis la seconde étape, décrite dans le chapitre 3, a été la synthèse • d'analogues de bisubstrats nécessaires pour l'exploration de la « poche de l'arginine ». Dans une dernière étape, décrite dans les chapitres 4 et 5, nous avons abordé la synthèse d'adduits SAM-peptide pouf pouvoir étudier le « domaine de fixation du peptide ». Dans le quatrième chapitre, la méthode de choix est la création d'un lien covalent entre une molécule hameçon électrophile etun peptide par chimie de click in-situ : par réaction de cycloaddition de Huisgen; par réaction entre des molécules hameçons électrophiles capables de piéger un peptide cystéine ou un peptide arginine. Ces essais se sont révélés infructueux et une nouvelle stratégie a été employée en utilisant des molécules ancres. Dansle cinquième chapitre des molécules ancres ont donc été préformés pour ensuite être testés en cocristallisation dans CARMl. / Protein aginine methyltransferases (PRMTs) have been implicated in a variety of biological processes. Coactivator-associated arginine methyltransferase 1 (CARM1 , also known as PRMT4) was identified as an enhancer of the transcriptional activation by several nuclear hormone receptors CARM1 is an enzyme which methylates the arginines of histones via a natural methyl donor, the SAdenosyh-Methionine (SAM). Recent studies have shown that CARM-1 is over-expressed in breastumors and in hormone dependent prostate tumors. The goal of this work is to understand at the molecular level the mode of binding of substrate/product arginine-containing peptides, reflectingstates prior and subsequent to methylation and the detailed mechanism of action of this protein. Several crystal structures of the catalytic domain of CARM1 have shown that cofactor-binding, such as S-Adenosyl-L -Homocysteine or sinefungin, produces large conformational changes in the catalytic domain. These crystal structures clearly illustrate that SAM binding is a prerequisite for peptide binding and build up the productive peptide binding site. Our strategy was to design fishhook molecules derivatives of the SAM capable of anchoring a mimic peptide of the histone H3 in order to test the co-crystallization in CARM1. Consequently, thanks to X-Ray structure, interactions involvement in the complexe CARM1/fishhook molecule/peptide could be determined. This strategy was do ne in three steps: the first one, described in the chapter 2, consisted in synthesizing SAManalogues with several modifications around sulfur atom. These compounds permitted to explore the "sulfonium pocket". The second step, described in chapter 3, consisted in synthesizing analogues of bisubstrats to explore "arginine binding pocket". Finally, the last step, described in the chapter 4 and 5, consisted in synthesizing SAM-peptide adducts to study "peptide binding domain". ln the chapter 4, the chosen method is the creation of covalent link between this molecule and a peptide by click chemistry in-situ: by reaction of Huisgen's cycloaddition; by reaction between electrophilic fishhook molecules capable of capturing with a cystein or arginine peptides. Unfortunately, ail of these trials have been unsuccessful. Consequently SAM-peptide adducts were performed to be co-crystallized in CARM1. This part was described in the last chapter.

Indiana University-Purdue University Indianapolis (IUPUI) / This dissertation describes structure-function studies of CXXC finger protein 1 (Cfp1), encoded by the CXXC1 gene, in order to determine the functional significance of Cfp1 protein domains and properties. Cfp1 is an important regulator of chromatin structure and is essential for mammalian development. Murine embryonic stem (ES) cells lacking Cfp1 (CXXC1-/-) are viable but demonstrate a variety of defects, including hypersensitivity to DNA damaging agents, reduced plating efficiency and growth, decreased global and gene-specific cytosine methylation, failure to achieve in vitro differentiation, aberrant histone methylation, and subnuclear mis-localization of Setd1A, the catalytic component of a histone H3K4 methyltransferase complex, and tri-methylated histone H3K4 (H3K4me3) with regions of heterochromatin. Expression of wild-type Cfp1 in CXXC1-/- ES cells rescues the observed defects, thereby providing a convenient method to assess structure-function relationships of Cfp1. Cfp1 cDNA expression constructs were stably transfected into CXXC1-/- ES cells to evaluate the ability of various Cfp1 fragments and mutations to rescue the CXXC1-/- ES cell phenotype. These experiments revealed that expression of either the amino half of Cfp1 (amino acids 1-367) or the carboxyl half of Cfp1 (amino acids 361-656) is sufficient to rescue the hypersensitivity to DNA damaging agents, plating efficiency, cytosine and histone methylation, and differentiation defects. These results reveal that Cfp1 contains redundant functional domains for appropriate regulation of cytosine methylation, histone methylation, and in vitro differentiation. Additional studies revealed that a point mutation (C169A) that abolishes DNA-binding activity of Cfp1 ablates the rescue activity of the 1-367 fragment, and a point mutation (C375A) that abolishes the interaction of Cfp1 with the Setd1A and Setd1B histone H3K4 methyltransferase complexes ablates the rescue activity of the 361-656 Cfp1 fragment. In addition, introduction of both point mutations (C169A and C375A) ablates the rescue activity of the full-length Cfp1 protein. These results indicate that retention of either DNA-binding or Setd1 association of Cfp1 is required to rescue hypersensitivity to DNA damaging agents, plating efficiency, cytosine and histone methylation, and in vitro differentiation. In contrast, confocal immunofluorescence analysis revealed that full-length Cfp1 is required to restrict Setd1A and histone H3K4me3 to euchromatic regions.

Protein Methyltransferasen sind oftmals fehlreguliert in Tumorzellen und stellen potenzielle Ziele in der Krebstherapie dar. Das SET und MYND Domain enthaltene Protein 2 (SMYD2) wurde als potenzielles Onkogen beschrieben und eine Überexpression korreliert mit einer schlechten Prognose. Für SMYD2 wurden verschiedene Substrate beschrieben u.a. Histon H3 und der Tumorsuppressor p53, allerdings ist die Biologie dieses Enzymes kaum verstanden. Durch die Entwicklung einer Testsubstanz zur spezifischen Hemmung von SMYD2 könnte ein möglicher therapeutischer Nutzen besser untersucht werden. Hierfür wurde ein zellulärer mechanistischer Test zur Messung der SMYD2 Aktivität mittels eines methylierungs-spezifischen Antikörpers etabliert. Mit Hilfe dieses Tests wurde BAY-598 als selektiver und potenter zellulärer Hemmer für SMYD2 identifiziert. Im weiteren Verlauf dieser Arbeit wurden mittels eines Proteomansatzes nach SMYD2 Überexpression hunderte neue zelluläre Lysinmethylierungen identifiziert. Hierbei wurde das AHNAK Protein als neues SMYD2-Substrat identifiziert und validiert. Die AHNAK Methylierung konnte in verschiedenen Zelllinien und im Muskelgewebe von Mäusen nachgewiesen werden. Im letzten Teil der Arbeit wurde die spezifische Testsubstanz BAY-598 genutzt, um verschiedene in der Literatur aufgekommene Hypothesen zur SMYD2 Funktion zu testen. Die vorliegende Arbeit hat dazu beigetragen die potente und selektive SMYD2 Testsubstanz BAY-598 zu entwickeln. Außerdem wurde mit AHNAK ein neues SMYD2 Substrat identifiziert und validiert. Die Relevanz des SMYD2 Enzymes und der AHNAK Methylierung erfordert weitere Forschungsarbeit, die durch die Bereitstellung der spezifischen Testsubstanz BAY-598 deutlich verbessert werden sollte. / Protein methyltransferases are often misregulated in tumor cells and display a potential target for cancer therapy. The SET and MYND domain containing protein 2 (SMYD2) was described as a potential oncogene and overexpression correlated with a worse prognosis. Several substrates for SMYD2 had been described among them histone H3 and p53. However, the biology of SMYD2 is poorly understood. By developing a small molecule inhibitor of SMYD2 its therapeutic role could be better evaluated. Therefore, a cellular mechanistic assay was developed using a methylation specific antibody. With that assay BAY-598 was identified as a potent and selective cellular inhibitor of SMYD2. In the following a proteomic approach revealed hundreds of novel cellular lysine methylation sites in SMYD2 overexpression cells. Among these AHNAK protein was validated as a novel SMYD2 substrate, which was present in several cell lines as well as in muscle of mice. Finally, BAY-598 was used to test several hypothesized functions of SMYD2 in different cell line models. Taken together, the current work strongly supported the development of the probe inhibitor BAY-598 and the discovery of AHNAK as a novel SMYD2 methylation substrate. The relevance of SMYD2 and AHNAK methylation needs further investigation, which should be supported by BAY-598.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.