Department of Human Virology, ENS-L, INSERM, U758, University of Lyon, Lyon I, F69364, France.
J Biol Chem. 2012 Nov 30;287(49):41210-7. doi: 10.1074/jbc.M112.403816. Epub 2012 Oct 17.
SAMHD1 is a newly identified restriction factor that targets lentiviruses in myeloid cells and is countered by the SIV(SM)/HIV-2 Vpx protein. By analyzing a large panel of Vpx mutants, we identify several residues throughout the 3-helix bundle predicted for Vpx that impair both its functionality and its ability to degrade SAMHD1. We determine that SAMHD1 is a strictly non-shuttling nuclear protein and that as expected WT Vpx localizes with it in the nucleus. However, we also identify a functional Vpx mutant with predominant cytoplasmic distribution that colocalizes with SAMHD1 in this location, suggesting that Vpx may also retain SAMHD1 in the cell cytoplasm, prior to its entry into the nucleus. Several mutations in Vpx were shown to affect the stability of Vpx, as well as Vpx:Vpx interactions. However, no strict correlation was observed between these parameters and the functionality of Vpx, implying that neither properties is absolutely required for this function and indicating that even unstable Vpx mutants may be very efficient in inducing SAMHD1 degradation. Overall, our analysis identifies several Vpx residues required for SAMHD1 degradation and points to a very efficient and plastic mechanism through which Vpx depletes this restriction factor.
SAMHD1 是一种新发现的限制因子，能够靶向髓系细胞中的慢病毒，而 SIV(SM)/HIV-2 的 Vpx 蛋白能够与之拮抗。通过分析大量的 Vpx 突变体，我们在 3 螺旋束中鉴定出几个残基，这些残基预测会影响 Vpx 的功能及其降解 SAMHD1 的能力。我们确定 SAMHD1 是一种严格的非穿梭核蛋白，而 WT Vpx 如其预期的那样与 SAMHD1 一起定位于核内。然而，我们还鉴定出一种具有主要细胞质分布的功能性 Vpx 突变体，与 SAMHD1 在该位置共定位，这表明 Vpx 可能也将 SAMHD1 保留在细胞质中，然后再进入细胞核。Vpx 中的几个突变被证明会影响 Vpx 的稳定性以及 Vpx:Vpx 相互作用。然而，这些参数与 Vpx 的功能之间没有观察到严格的相关性，这意味着这两个特性都不是该功能所必需的，并且表明即使是不稳定的 Vpx 突变体也可能非常有效地诱导 SAMHD1 降解。总体而言，我们的分析确定了几个 Vpx 残基，这些残基对于 SAMHD1 的降解是必需的，并指出了一种非常有效和灵活的机制，通过该机制，Vpx 能够耗尽这种限制因子。
