{"id":5682,"date":"2015-12-08T19:25:13","date_gmt":"2015-12-08T19:25:13","guid":{"rendered":"https:\/\/mycor.iam.inrae.fr\/IAM\/?p=5682"},"modified":"2015-12-08T19:28:48","modified_gmt":"2015-12-08T19:28:48","slug":"phd-defense","status":"publish","type":"post","link":"https:\/\/mycor.iam.inrae.fr\/IAM\/?p=5682","title":{"rendered":"PhD Defense: H. Pegeot"},"content":{"rendered":"

The defense will be held the 11th December\u00a0at 14h00\u00a0in\u00a0Amphitheater 7,<\/strong>\u00a0Facult\u00e9 des Sciences<\/strong>, Boulevard des Aiguillettes, Vandoeuvre.<\/p>\n

Etude des glutathion transf\u00e9rases de la classe Phi du peuplier (Populus trichocarpa<\/em>) : caract\u00e9risation structurale, enzymatique et recherche de mol\u00e9cules cibles.<\/strong><\/p>\n

R\u00e9sum\u00e9\u00a0:<\/span><\/strong> Les glutathion transf\u00e9rases (GSTs) constituent une famille multig\u00e9nique d\u2019enzymes pr\u00e9sentes dans les trois domaines du vivant. Cette pr\u00e9sence ubiquitaire souligne l\u2019origine sans doute tr\u00e8s ancienne de ces enzymes ainsi que des fonctions fondamentales conserv\u00e9es au cours de l\u2019\u00e9volution. Ces enzymes sont impliqu\u00e9es notamment dans la d\u00e9toxication cellulaire de mol\u00e9cules toxiques et dans le m\u00e9tabolisme secondaire. Les analyses phylog\u00e9n\u00e9tiques regroupent les GSTs des organismes photosynth\u00e9tiques au sein de quatorze classes\u00a0qui peuvent \u00eatre s\u00e9par\u00e9es en deux grands groupes selon le r\u00e9sidu catalytique\u00a0: les GSTs \u00e0 s\u00e9rine catalytique qui poss\u00e8dent des activit\u00e9s de conjugaison du glutathion (GSH) et\/ou peroxydase tandis que les GSTs \u00e0 cyst\u00e9ine catalytique pr\u00e9sentent des activit\u00e9s thioltransf\u00e9rase, d\u00e9shydroascorbate r\u00e9ductase et de d\u00e9glutathionylation. Les GSTs \u00e0 s\u00e9rine catalytique de la classe Phi (GSTF) sont pr\u00e9sentes chez les organismes photosynth\u00e9tiques et certains basidiomyc\u00e8tes. Chez les plantes, cette classe comprend un nombre de g\u00e8nes plus important que les autres classes de GSTs. Ceux-ci sont parmi les plus r\u00e9gul\u00e9s en r\u00e9ponse \u00e0 divers stress et ils ont \u00e9t\u00e9 fortement \u00e9tudi\u00e9s chez les plantes c\u00e9r\u00e9ali\u00e8res en raison de l\u2019activit\u00e9 de d\u00e9toxication des herbicides des prot\u00e9ines correspondantes. Pourtant, \u00e0 quelques exceptions pr\u00e8s, les r\u00f4les physiologiques des GSTFs restent inconnus et la redondance d\u2019isoformes dans cette classe reste incomprise. Par des approches mol\u00e9culaires, biochimiques et structurales, l\u2019analyse structure-fonction des huit GSTFs de l\u2019arbre mod\u00e8le Populus trichocarpa<\/em> a \u00e9t\u00e9 r\u00e9alis\u00e9e au cours de cette th\u00e8se. L\u2019analyse phylog\u00e9n\u00e9tique des GSTFs chez les organismes photosynth\u00e9tiques a montr\u00e9 que cette classe est apparue au moment de l\u2019apparition terrestre des v\u00e9g\u00e9taux et que diff\u00e9rents groupes pouvaient \u00eatre identifi\u00e9s avec des motifs catalytiques distincts. L\u2019analyse transcriptionnelle a montr\u00e9 que les g\u00e8nes relatifs aux GSTFs de peuplier sont principalement exprim\u00e9s dans les fleurs femelles, les p\u00e9tioles et les fruits. Certains aspects du m\u00e9canisme r\u00e9actionnel ont \u00e9t\u00e9 caract\u00e9ris\u00e9s en d\u00e9terminant notamment les param\u00e8tres cin\u00e9tiques et d\u2019interaction des huit GSTFs et de plusieurs variants mut\u00e9s pour des r\u00e9sidus cl\u00e9s vis-\u00e0-vis de substrats mod\u00e8les. Les structures de cinq des huit GSTFs ont \u00e9t\u00e9 r\u00e9solues et ces prot\u00e9ines dim\u00e9riques adoptent un repliement GST canonique et des sp\u00e9cificit\u00e9s structurales au niveau du site actif ont pu \u00eatre observ\u00e9es. De plus, au regard de la capacit\u00e9 des orthologues des GSTFs \u00e0 lier des hormones et des flavono\u00efdes ainsi que de l\u2019expression r\u00e9currente des GSTFs de peuplier dans les fruits et les fleurs femelles, deux organes riches en ces mol\u00e9cules, il peut \u00eatre suppos\u00e9 qu\u2019elles ont aussi des propri\u00e9t\u00e9s de type ligandine. Des r\u00e9sultats pr\u00e9liminaires ont \u00e9galement \u00e9t\u00e9 obtenus pour la recherche de substrats physiologiques \u00e0 partir de m\u00e9tabolites extraits de diff\u00e9rents organes de peuplier. A terme, l\u2019identification de ces substrats permettra de d\u00e9terminer le mode d\u2019action (catalytique vs<\/em> ligandine) de chaque enzyme et d\u2019identifier clairement les fonctions in planta<\/em> de ces enzymes.<\/p>\n

Mots cl\u00e9s\u00a0:<\/span><\/strong> glutathion transf\u00e9rase\u00a0; Populus trichocarpa<\/em>\u00a0; Phi\u00a0; structures cristallographiques\u00a0; m\u00e9canismes enzymatiques\u00a0; recherche de substrats<\/p>\n

Abstract:<\/span><\/strong> Glutathione transferases (GSTs) belong to a multigenic family whose presence in most eukaryotes, prokaryotes and archaea reflects their widespread nature and very likely important functions. These enzymes represent a major group of enzymes involved in xenobiotic detoxification and secondary metabolism. From the most recent genomic and phylogenetic analyses, the GST family is subdivided into 14 classes that can be separated into two main groups based on the catalytic residue which is either a serine (Ser-GST) or a cysteine (Cys-GST). Ser-GSTs usually catalyze glutathione (GSH) conjugation and\/or peroxide reduction. On the other hand, Cys-GSTs cannot perform GSH-conjugation reactions but instead catalyze thiol-transferase, dehydroascorbate reductase and deglutathionylation reactions. Ser-GSTs from the Phi class (GSTF) are present in photosynthetic organisms and some basidiomycetes. This class is composed of a large number of genes compared to other GST classes which are amongst the most stress-inducible. The corresponding proteins have been extensively studied in crops with regard to their detoxification activities toward herbicides. However, with a few exceptions, very little is known about their roles in planta<\/em> and it is not well understood why this class has expanded. By combining molecular, cellular, biochemical and structural approaches, the eight isoforms from the model tree Populus trichocarpa<\/em> have been characterized during this PhD project. Phylogenetic analysis of GSTFs in the green lineage shows that the apparition of this class is concomitant with the appearance of terrestrial plants and that different groups can be distinguished based on the active site signature. RT-PCR analysis of the eight isoforms of GSTFs showed that transcripts mostly accumulate in female flowers, petioles and fruits. Some aspects of the reaction mechanism have been characterized by determining kinetic parameters of the eight poplar GSTFs and of several mutated variants for key residues towards model substrates. The structures of five GSTFs have been solved and these dimeric proteins display a typical GST fold but specificities have been observed at the catalytic site level. Moreover, considering the demonstrated capacity of GSTF orthologs to bind hormones, anthocyanins or flavonoids, and the consistent high expression of poplar GSTFs in female flowers and fruits, two organs rich in these molecules, we speculate that they may also possess ligandin properties. Preliminary results have been obtained regarding the nature of the substrates in various poplar organs by analyzing protein thermostability in the presence of putative ligands. In order to assess whether a functional redundancy between poplar Phi GSTs exists and to identify their mode of action (catalytic vs<\/em> ligandin functions), we started to isolate and identify physiological substrates.<\/p>\n

Key words:<\/span><\/strong> Glutathione transferase; Populus trichocarpa<\/em>; Phi; crystal structures; enzymatic mechanisms; research of substrates.<\/p>\n","protected":false},"excerpt":{"rendered":"

The defense will be held the 11th December\u00a0at 14h00\u00a0in\u00a0Amphitheater 7,\u00a0Facult\u00e9 des Sciences, Boulevard des Aiguillettes, Vandoeuvre. Etude des glutathion transf\u00e9rases de la classe Phi du peuplier (Populus trichocarpa) : caract\u00e9risation structurale, enzymatique et recherche de mol\u00e9cules cibles. R\u00e9sum\u00e9\u00a0: Les glutathion … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[],"class_list":["post-5682","post","type-post","status-publish","format-standard","hentry","category-seminarmeeting"],"_links":{"self":[{"href":"https:\/\/mycor.iam.inrae.fr\/IAM\/index.php?rest_route=\/wp\/v2\/posts\/5682","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mycor.iam.inrae.fr\/IAM\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mycor.iam.inrae.fr\/IAM\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mycor.iam.inrae.fr\/IAM\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/mycor.iam.inrae.fr\/IAM\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5682"}],"version-history":[{"count":0,"href":"https:\/\/mycor.iam.inrae.fr\/IAM\/index.php?rest_route=\/wp\/v2\/posts\/5682\/revisions"}],"wp:attachment":[{"href":"https:\/\/mycor.iam.inrae.fr\/IAM\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5682"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mycor.iam.inrae.fr\/IAM\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5682"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mycor.iam.inrae.fr\/IAM\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5682"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}