title: HIV-2 and SIVmac accessory virulence factor Vpx down-regulates SAMHD1 enzyme catalysis prior to proteasome-dependent degradation.
abstract: SAMHD1, a dGTP-regulated deoxyribonucleoside triphosphate (dNTP) triphosphohydrolase, down-regulates dNTP pools in terminally differentiated and quiescent cells, thereby inhibiting HIV-1 infection at the reverse transcription step. HIV-2 and simian immunodeficiency virus (SIV) counteract this restriction via a virion-associated virulence accessory factor, Vpx (Vpr in some SIVs), which loads SAMHD1 onto CRL4-DCAF1 E3 ubiquitin ligase for polyubiquitination, programming it for proteasome-dependent degradation. However, the detailed molecular mechanisms of SAMHD1 recruitment to the E3 ligase have not been defined. Further, whether divergent, orthologous Vpx proteins, encoded by distinct HIV/SIV strains, bind SAMHD1 in a similar manner, at a molecular level, is not known. We applied surface plasmon resonance analysis to assess the requirements for and kinetics of binding between various primate SAMHD1 proteins and Vpx proteins from SIV or HIV-2 strains. Our data indicate that Vpx proteins, bound to DCAF1, interface with the C terminus of primate SAMHD1 proteins with nanomolar affinity, manifested by rapid association and slow dissociation. Further, we provide evidence that Vpx binding to SAMHD1 inhibits its catalytic activity and induces disassembly of a dGTP-dependent oligomer. Our studies reveal a previously unrecognized biochemical mechanism of Vpx-mediated SAMHD1 inhibition: direct down-modulation of its catalytic activity, mediated by the same binding event that leads to SAMHD1 recruitment to the E3 ubiquitin ligase for proteasome-dependent degradation.
authors.affiliation: Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15260, USA.
authors.forename: Maria
authors.initials: M
authors.lastname: DeLucia
authors.forename: Jennifer
authors.initials: J
authors.lastname: Mehrens
authors.forename: Ying
authors.initials: Y
authors.lastname: Wu
authors.forename: Jinwoo
authors.initials: J
authors.lastname: Ahn
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002384:Catalysis; D003432:Cross-Linking Reagents / Q000494:pharmacology; D057809:HEK293 Cells; D015498:HIV-2 / Q000378:metabolism*; D006801:Humans; D008253:Macaca mulatta; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D000076106:SAM Domain and HD Domain-Containing Protein 1; D017386:Sequence Homology, Amino Acid; D015302:Simian Immunodeficiency Virus / Q000378:metabolism*; D020349:Surface Plasmon Resonance; D025801:Ubiquitin / Q000378:metabolism; D054334:Viral Regulatory and Accessory Proteins / Q000378:metabolism*; D037521:Virulence Factors / Q000378:metabolism
chemical_list: D003432:Cross-Linking Reagents; D025801:Ubiquitin; C074286:VPX protein, Human immunodeficiency virus 2; C513059:VPX protein, Simian immunodeficiency virus; D054334:Viral Regulatory and Accessory Proteins; D037521:Virulence Factors; D000076106:SAM Domain and HD Domain-Containing Protein 1; C484280:SAMHD1 protein, human; D046988:Proteasome Endopeptidase Complex; D020559:Monomeric GTP-Binding Proteins
keywords: Enzyme Turnover; Enzymes; HIV; Restriction Factors; Ubiquitin Ligase; Ubiquitination; Virulence Factors