Developing a Disulfide Replacement Picture of APOBEC3G

Abstract

The human protein APOBEC3G (A3G) interferes with HIV infection by acting as a cytidine deaminase, an enzyme that induces numerous mutations in HIV’s genetic material that ultimately destroy it. But A3G is only successful at this for a time. The HIV protein viral infectivity factor (Vif) destroys A3G. Developing a way to mask A3G from Vif is a major therapeutic goal. Uncovering the three-dimensional structure of A3G is crucial to rational drug design. The catalytic C-terminal domain of A3G has been solved, but the crucial Vif-interacting N-terminal domain remains invisible to medicinal chemists. A major obstacle toward this goal is the N-terminal domain’s poor solubility. Here we explore a novel technique, disulfi de replacement, in which pairs of cysteine residues are incorporated into the protein at hypothetically close positions and checked for disulfi de bonding. We isolated a model peptide containing a disulfi de bond from its reduced form, and we observed an engineered disulfi de from the Ctd of A3G at two residues known to be spatially close. However, the sensitivity of the approach in digested peptide samples must be improved. We would like to acknowledge Yongjian Lu, Takahide Kono, the Chemistry Department Mass Spectrometry Facility, and all the other members of the Matsuo lab for their support.