Crystallographic And Functional Studies On The Flavin Dependent Thymidylate Synthase And Primary Crystallographic Studies On CagF Protein Both From Helicobacter Pylori

This thesis is constituted of two parts. The first part is the crystallographic and functional studies on the flavin dependent thymidylate synthase from Helicobacter pylori.The ThyX enzymes identified recently in various bacteria, including some important human pathogens such as Helicobacter pylori and Mycobacterium tuberculosis, are flavin dependent thymidylate synthases that functions in places of the classic ThyA enzymes in the biosynthesis of dTMP, one of the building blocks of DNA. They are promising targets for the development of novel antibiotics because homologous enzymes are not present in humans. In this study, we purified and crystallized H. pylori ThyX in complex with flavin adenine dinucleotide (FAD) and dUMP and collected a diffraction data set to 2.5(A|。) resolution. The structure was determined by the molecular replacement method. On the basis of structural analysis, the ThyX holoenzyme model in its initial state and the catalysis mechanism were hypothesized.The second part mainly focused on the primary crystallographic studies of CagF, a protein from type IV secretion system (T4SS) encoded by cag PAI of Helicobacter pylori. T4SS is involved in mediating the injection of virulence factor CagA into mammalian host cells, the latter is closely related with various gastric diseases such as gastritis, gastric ulcer and gastric cancer. CagF is proposed to be a protein with aunique chaperone-like function that recruits CagA to the T4SS, it is localized at both the inner bacterial membrane and the cytoplasm. The structure of CagF would shed lights on the secreting mechanism of CagA. Through our continuous effort, we obtained the crystals of CagF successfully. Due to the small size of the crystals, this work is now still in progress.