| Summary: | 碩士 === 國立陽明大學 === 生命科學暨基因體科學研究所 === 98 === To date, the apolipoprotein B mRNA-editing catalytic proteins (APOBEC) including APOBEC1-4 and activation-induced deaminase (AID), are the only identified C-to-U editing deaminases involved in gene diversity and antiviral activity. Only the primate APOBEC3 genes have expanded into a tandem array of genes termed APOBEC3A-H. Among them, APOBEC3G is able to restrict the infection of viral infectivity-factor-defective HIV-1 through C-to-U editing of the viral nascent minus-strand DNA. This protein contains two putative deaminase domains, in which the C-terminal domain (APOBEC3GC) is responsible for the deaminase activity. In this thesis, the wild-type APOBEC3GC recombinant protein was first expressed and isolated successfully, with significant deaminase activity on a variety of ssDNA. After extensive screening and refinement of APOBEC3GC with a 14-mer ssDNA, some crystals were grown and diffracted x-ray to 3 ?痋@resolution. Future crystallization refinement and structure determination are under investigation. Recently, several structures of the wild-type and mutant APOBEC3GC have been determined by NMR and X-ray diffraction methods. These structures display significant differences and hence distinct ssDNA-binding residues are predicted. Particularly, the functional roles of R215 and R313 are inconclusive. These two arginine residues are corresponding to R24 and R112 in AID, and the R24W and R112C mutants are the hot spots in the hyper-IgM patients. The R215W and R313C mutants were then generated and characterized. Both mutants display no detectable deaminase activity. R215W exhibits similar circular dichroism spectra compared with wild type APOBEC3GC. The ssDNA binding abilities are monitored by electrophoretic mobility shift assay, filter binding assay and isothermal titration calorimetry. The preliminary data suggest that the replacement of R215 with tryptophan decreases the ssDNA binding, but increase the Tm value by ~5 oC.
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