HIV-2 and SIVmac Accessory Virulence Factor Vpx Down-regulates SAMHD1 Enzyme Catalysis Prior to Proteasome-dependent Degradation
HIV-2 and SIVmac Accessory Virulence Factor Vpx Down-regulates SAMHD1 Enzyme Catalysis Prior to Proteasome-dependent Degradation
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DOI：
10.1074/jbc.m113.469007
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发表时间：
2013-06-28
影响因子：
4.8
通讯作者：
Ahn, Jinwoo
中科院分区：
文献类型：
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作者：
DeLucia, Maria;Mehrens, Jennifer;Ahn, Jinwoo
SAMHD1是一种由dgtp调控的脱氧核糖核苷三磷酸（dNTP）三磷酸水解酶，可下调终分化和静止细胞中的dNTP池，从而在逆转录阶段抑制HIV-1感染。HIV-2和猴免疫缺陷病毒（SIV）通过病毒粒子相关的毒力辅助因子Vpx（在一些SIV中是Vpr）抵消了这种限制，Vpx将SAMHD1装载到CRL4-DCAF1 E3泛素连接酶上进行多泛素化，并对其进行蛋白酶体依赖性降解编程。然而，SAMHD1招募到E3连接酶的详细分子机制尚未明确。此外，由不同HIV/SIV毒株编码的不同的同源Vpx蛋白是否在分子水平上以类似的方式结合SAMHD1尚不清楚。我们应用表面等离子体共振分析来评估不同灵长类动物SAMHD1蛋白与SIV或HIV-2毒株Vpx蛋白结合的需求和动力学。我们的数据表明，Vpx蛋白与DCAF1结合，与灵长类动物SAMHD1蛋白的C端具有纳摩尔亲和力，表现为快速结合和缓慢解离。此外，我们提供的证据表明，Vpx结合SAMHD1抑制其催化活性，并诱导dgtp依赖性低聚物的分解。我们的研究揭示了vpx介导的SAMHD1抑制的一个以前未被认识的生化机制：直接下调其催化活性，由导致SAMHD1募集到E3泛素连接酶以进行蛋白酶体依赖性降解的相同结合事件介导。
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.