Year of Publication
Doctor of Philosophy (PhD)
Dr Jürgen Rohr
Gilvocarcin V (GV) and ravidomycin (RMV) exhibit excellent antitumor activities in the presence of near-UV light at low concentration maintaining a low in vivo cytotoxicity. Although, the exact molecular mechanism for in vivo actions of these antibiotics has yet to be determined, a [2+2] cycloaddition reaction of the vinyl side chain with DNA thymidine residues in addition to the inhibition of topoisomerase II and DNAhistone H3 cross-linking are reported for the GV’s mechanism of action. Such activities have made these molecules interesting candidates for the biosynthetic investigation to generate analogues with improved activity/solubility. Previous biosynthetic studies have suggested that the GV biosynthetic pathway involves a number of synchronously occurring transformations leading to the oxidative C-C bond cleavage and other intriguing biosynthetic reactions, such as the vinyl side chain formation, methylations, Cglycosylation and dehydrogenation. Although gene inactivation results identified many candidate genes whose corresponding enzymes are involved in these biochemical transformations, their exact functional roles and the identity of their natural substrates remained elusive. To provide more insights into these complex biochemical tranfrormations, three specific aims were set up.
Specific aim 1 was to clone and characterize the RMV biosynthetic gene cluster. Through the comparison of GV cluster with the RMV cluster, the genes encoding the biosynthesis of sugar and tetracyclic aromatic moieties were identified. RavGT, the sole glycosyltransferase of the RMV cluster has demonstrated to have unprecedented sugar donor substrate flexibility, transferring an amino-pyranose sugar as well as a neutral furanose sugar.
Specific aim 2 was to characterize all of the TDP-D-ravidosamine biosynthetic enzymes. The aim also included to a one-pot enzymatic synthetic protocol for the routine production of TDP-D-ravidosamine.
Specific aim 3 focussed on a total enzymatic synthesis of defucogilvocarcin M (defucoGM), the polyketide-derived core of GV and RMV. This aim clearly identified the minimal enzymes required to biosynthesize the complex architecture of defucoGM from the simple building blocks acetate and malonate. In addition, the GV-pathway enzyme GilR was fully characterized. Through in vitro studies, GilR was shown to catalyze the dehydrogenation of hemiacetal moiety of the penultimate intermediate pregilvocarcin V to the lactone moiety of GV at the last step.
Kharel, Madan Kumar, "DISSECTING THE BIOSYNTHESES OF GILVOCARCINS AND RAVIDOMYCINS" (2010). University of Kentucky Doctoral Dissertations. 96.