Angle Small X-ray Scattering Provides Insight into the Mode of RNAMediated Regulation of APOBEC3G Anti-HIV Activity
*,1Joseph E. Wedekind, 2Richard Gillilan, 1Alena Janda, 1Jolanta Krucinska, 1Jason D. Salter, 1 Ryan P. Bennett, 3Jay Raina & 1Harold C. Smith
1
Department of Biochemistry & Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA 2 Macromolecular Structure Facility at the Cornell High-Energy Synchrotron Source (MacCHESS), Cornell University, Ithaca, NY 14853, USA 3 Immunodiagnostics Inc., Woburn, MA 01801, USA
*correspondence to: [e-mail]
Human APOBEC3G (hA3G) is an innate deoxycytidine-to-deoxyuridine deaminase that restricts HIV-1 infectivity by introducing catastrophic mutations into the viral genome in the absence of the HIV-1 factor vif. hA3G from HIV-permissive, activated CD4+ T-cells exists as an inactive, high-molecular-mass (HMM) complex that can be transformed in vitro into an enzymatically active, low-molecular-mass (LMM) variant comparable to that identified in HIVnon-permissive CD4+ T-cells. Similarly, hA3G has been detected in viral capsids as an inactivated ribonucleoprotein activity whose restoration depends upon the RNase H function of reverse transcriptase. Collectively, these data support a model that suggests inactivation of hA3G depends on RNA. To elucidate how RNA influences the structural organization of hA3G, we determined low resolution structures of recombinantly expressed HMM- and LMM-variants by small angle X-ray scattering. The results indicated that LMM particles have an extended shape, dissimilar to known cytidine deaminase crystal structures. Structure-based biochemical experiments corroborated these observations and suggested that each LMM particle comprises a tail-to-tail dimer of identical subunits. Additional studies indicated that rec...