Lukhele Sabelo, Cohen Éric A
Laboratory of Human Retrovirology, Institut de Recherches Cliniques de Montréal (IRCM), 110, Pine Avenue West, Montreal, QC, H2W 1R7, Canada.
Division of Experimental Medicine, McGill University, Montreal, QC, H3A 1A3, Canada.
Retrovirology. 2017 Mar 14;14(1):18. doi: 10.1186/s12977-017-0345-6.
BST2 inhibits HIV-1 release by tethering nascent virions to the surface of infected cells. HIV-1 Vpu overcomes this restriction by removing BST2 from viral budding sites via BST2 intracellular trapping and sequestration, surface downregulation and/or displacement mechanisms. Vpu is composed of a short luminal tail, a transmembrane domain (TMD) and a cytoplasmic hinge region that is followed by two helices. BST2 counteraction relies on the ability of Vpu to physically bind BST2 through TMD interactions and recruit the clathrin-dependent trafficking machinery via a canonical acidic di-leucine signalling motif within the helix-2 of Vpu. The highly conserved Vpu transmembrane-proximal hinge region encompasses residues that resemble an acidic leucine-based trafficking motif, whose functional roles are currently ill-defined. In this study, we investigated the contribution of these residues towards Vpu-mediated BST2 antagonism.
We show that while these conserved residues have no intrinsic activity on the cellular distribution of Vpu in the absence of BST2, they regulate the ability of Vpu to bind to BST2 and, consequently, govern both BST2-dependent trafficking properties of the protein as well as its co-localization with BST2. Moreover, these residues, particularly a glutamic acid residue positioned immediately following the TMD, are a determinant not only for efficient targeting of BST2, but also binding and degradation of CD4, another host membrane protein targeted by Vpu. Mechanistically, our data are consistent with a role of these residues in the maintenance of the Vpu TMD conformational configuration such that interactions with membrane-associated host targets are favoured.
Altogether, this work demonstrates an important regulatory role of the transmembrane-proximal Vpu hinge region residues towards enabling the protein to efficiently engage its target host proteins. Thus, this highly conserved, cytosolic Vpu hinge region may represent an attractive target for the development of anti-Vpu inhibitors.
BST2通过将新生病毒体拴系到受感染细胞表面来抑制HIV-1释放。HIV-1 Vpu通过BST2的细胞内捕获和隔离、表面下调和/或置换机制，将BST2从病毒出芽位点移除，从而克服这种限制。Vpu由一个短的腔内尾部、一个跨膜结构域（TMD）和一个细胞质铰链区组成，该铰链区后面跟着两个螺旋。Vpu对BST2的拮抗作用依赖于Vpu通过TMD相互作用与BST2物理结合的能力，并通过Vpu螺旋2内的一个典型酸性双亮氨酸信号基序募集网格蛋白依赖性运输机制。高度保守的Vpu跨膜近端铰链区包含类似于基于酸性亮氨酸的运输基序的残基，其功能作用目前尚不清楚。在本研究中，我们研究了这些残基对Vpu介导的BST2拮抗作用的贡献。
我们发现，虽然在没有BST2的情况下，这些保守残基对Vpu在细胞内的分布没有内在活性，但它们调节Vpu与BST2结合的能力，从而控制该蛋白依赖于BST2的运输特性及其与BST2的共定位。此外，这些残基，特别是位于TMD之后的一个谷氨酸残基，不仅是BST2有效靶向的决定因素，也是Vpu靶向的另一种宿主膜蛋白CD4的结合和降解的决定因素。从机制上讲，我们的数据与这些残基在维持Vpu TMD构象构型中的作用一致，从而有利于与膜相关宿主靶点的相互作用。
总之，这项工作证明了跨膜近端Vpu铰链区残基在使该蛋白有效地与靶宿主蛋白结合方面的重要调节作用。因此，这个高度保守的胞质Vpu铰链区可能是开发抗Vpu抑制剂的一个有吸引力的靶点。
