title: APOBEC2 is a monomer in solution: implications for APOBEC3G models.
abstract: Although the physiological role of APOBEC2 is still largely unknown, a crystal structure of a truncated variant of this protein was determined several years ago [Prochnow, C. (2007) Nature445, 447-451]. This APOBEC2 structure had considerable impact in the HIV field because it was considered a good model for the structure of APOBEC3G, an important HIV restriction factor that abrogates HIV infectivity in the absence of the viral accessory protein Vif. The quaternary structure and the arrangement of the monomers of APOBEC2 in the crystal were taken as being representative for APOBEC3G and exploited in explaining its enzymatic and anti-HIV activity. Here we show, unambiguously, that in contrast to the findings for the crystal, APOBEC2 is monomeric in solution. The nuclear magnetic resonance solution structure of full-length APOBEC2 reveals that the N-terminal tail that was removed for crystallization resides close to strand β2, the dimer interface in the crystal structure, and shields this region of the protein from engaging in intermolecular contacts. In addition, the presence of the N-terminal region drastically alters the aggregation propensity of APOBEC2, rendering the full-length protein highly soluble and not prone to precipitation. In summary, our results cast doubt on all previous structure-function predictions for APOBEC3G that were based on the crystal structure of APOBEC2.
authors.affiliation: Department of Structural Biology, University of Pittsburgh School of Medicine, and Pittsburgh Center for HIV Protein Interactions, Pittsburgh, Pennsylvania 15261, United States.
authors.forename: Troy C
authors.initials: TC
authors.lastname: Krzysiak
authors.forename: Jinwon
authors.initials: J
authors.lastname: Jung
authors.forename: James
authors.initials: J
authors.lastname: Thompson
authors.forename: David
authors.initials: D
authors.lastname: Baker
authors.forename: Angela M
authors.initials: AM
authors.lastname: Gronenborn
mesh_terms: D000071480:APOBEC-3G Deaminase; D000595:Amino Acid Sequence; D003564:Cytidine Deaminase / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D016415:Sequence Alignment; D012996:Solutions
chemical_list: D012996:Solutions; D000071480:APOBEC-3G Deaminase; C464924:APOBEC3G protein, human; D003564:Cytidine Deaminase