Vibrio cholerae canlısında 6-4 fotoliyazının tespiti ve karakterize edilmesi

Ultra-violet (UV) light introduces mutagenic damages to the DNA in the form of pyrimidine dimers. If not repaired, these damages may cause carcinogenic and lethal effects on the organism. Photolyases (PHRs) are the ancient flavoproteins that repair UV-induced lesions in a blue light-dependent mechanism. PHRs, according to substrate specificity, are divided into two functional groups: CPD PHRs that repair cyclobutane pyrimidine dimers (CPD) and (6-4) PHRs that repair pyrimidine-pyrimidone (6-4) photoproducts [(6-4) PP]. Although CPD photolyases are distributed among the three domains of life, (6-4) PHRs were thought to be restricted to eukaryotes. Vibrio cholerae (O1 bivar Tor str. N16961) possesses three cryptochrome/photolyase family (CPF) members: VcPhr, a CPD photolyase; and two single-strand CPD PHRs VcCry1 and VcCry2. This dissertation presents the first (6-4) PHR in V. cholerae, named Vc (6-4) FeS-BCP. The enzyme belongs to newly discovered 'iron-sulphur cluster containing bacterial cryptochromes and photolyases' (FeS-BCP) class. Vc (6-4) FeS-BCP is the third enzyme characterized in this class. (6-4) repair activity of the Vc (6-4) FeS-BCP was demonstrated in vitro by DNA slot-blot repair assay. In vivo contribution of the protein to photoreactivation of the organism was presented by photoreactivation-complementation assay. Structural characterization of the protein via computational and experimental methods suggest that protein possesses FAD catalytic cofactor, DMRL photoantenna and [4FeS-4S] cluster.