title: A model for oligomeric regulation of APOBEC3G cytosine deaminase-dependent restriction of HIV.
abstract: APOBEC3G (A3G) restricts HIV-1 infection by catalyzing processive C --> U deaminations on single-stranded DNA (ssDNA) with marked 3' --> 5' deamination polarity. Here we show that A3G exists in oligomeric states whose composition is dictated primarily by interactions with DNA, with salt playing an important, yet secondary, role. Directional deaminations correlate with the presence of dimers, tetramers, and larger oligomers observed by atomic force microscopy, and random deaminations appear to correlate mainly with monomers. The presence of a 30-nt weakly deaminated "dead" zone located at the 3'-ssDNA end implies the presence of a preferred asymmetric direction for A3G catalysis. Single turnover reaction rates reveal a salt-dependent inhibition of C deamination toward the 3'-ssDNA region, offering a molecular basis underlying A3G deamination polarity. Presteady state analysis demonstrates rapid diffusion-limited A3G-ssDNA binding, a slower salt-dependent conformational change, possibly indicative of DNA wrapping, and long (5-15 min) protein-DNA complex lifetimes. We suggest that diverse A3G oligomerization modes contribute to the human immunodeficiency virus, type 1, proviral DNA mutational bias.
authors: Department of Biological Sciences and Chemistry, University of Southern California, Los Angeles, California 90089-2910, USA.
authors: Linda
authors: L
authors: Chelico
authors: Elizabeth J
authors: EJ
authors: Sacho
authors: Dorothy A
authors: DA
authors: Erie
authors: Myron F
authors: MF
authors: Goodman
mesh_terms: D000071480:APOBEC-3G Deaminase; D000818:Animals; D002384:Catalysis; D003564:Cytidine Deaminase / Q000737:chemistry*; D004247:DNA / Q000737:chemistry; D004252:DNA Mutational Analysis; D004277:DNA, Single-Stranded / Q000737:chemistry; D006678:HIV / Q000378:metabolism*; D006801:Humans; D007313:Insecta; D015636:Magnesium Chloride / Q000737:chemistry; D018625:Microscopy, Atomic Force; D008954:Models, Biological; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D013997:Time Factors
chemical_list: D004277:DNA, Single-Stranded; D015636:Magnesium Chloride; D004247:DNA; D000071480:APOBEC-3G Deaminase; C464924:APOBEC3G protein, human; D003564:Cytidine Deaminase