Assessing the catalytic activity of APOBEC3 cytidine deaminases

APOBEC3 cytidine deaminases inhibit HIV-1 by a combination of editing and non-editing mechanisms. Haplotypes with distinct antiviral phenotypes have been described for APOBEC3H (A3H) and APOBEC3G (A3G).We hypothesized that differences in antiviral activity between these APOBEC3 haplotypes were due to variation in catalytic activity. We first assessed the deaminase activity of A3H variants using an E. coli mutator assay. We found a strong correlation between protein expression and catalytic activity, suggesting that single nucleotide polymorphisms (SNPs) in A3H do not directly affect deaminase activity. We next analyzed the deaminase activity of four natural A3G haplotypes. Using the E. coli mutator assay, we found that A3G-H186R and A3G-R255H/Q275E were less catalytically active than A3G-WT while the catalytic activity of A3G-Q275E was enhanced.APOBEC3 SNPs may directly affect the activity of these intracellular defense molecules since A3G-H186R has been associated with rapid progression to AIDS.