Sun Zhen-Yu J, Cheng Yuxing, Kim Mikyung, Song Likai, Choi Jaewon, Kudahl Ulrich J, Brusic Vladimir, Chowdhury Barnali, Yu Lu, Seaman Michael S, Bellot Gaëtan, Shih William M, Wagner Gerhard, Reinherz Ellis L
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
Laboratory of Immunobiology and Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA.
J Mol Biol. 2014 Mar 6;426(5):1095-108. doi: 10.1016/j.jmb.2013.09.030. Epub 2013 Sep 26.
HIV-1 (human immunodeficiency virus type 1) uses its trimeric gp160 envelope (Env) protein consisting of non-covalently associated gp120 and gp41 subunits to mediate entry into human T lymphocytes. A facile virus fusion mechanism compensates for the sparse Env copy number observed on viral particles and includes a 22-amino-acid, lentivirus-specific adaptation at the gp41 base (amino acid residues 662-683), termed the membrane proximal external region (MPER). We show by NMR and EPR that the MPER consists of a structurally conserved pair of viral lipid-immersed helices separated by a hinge with tandem joints that can be locked by capping residues between helices. This design fosters efficient HIV-1 fusion via interconverting structures while, at the same time, affording immune escape. Disruption of both joints by double alanine mutations at Env positions 671 and 674 (AA) results in attenuation of Env-mediated cell-cell fusion and hemifusion, as well as viral infectivity mediated by both CD4-dependent and CD4-independent viruses. The potential mechanism of disruption was revealed by structural analysis of MPER conformational changes induced by AA mutation. A deeper acyl chain-buried MPER middle section and the elimination of cross-hinge rigid-body motion almost certainly impede requisite structural rearrangements during the fusion process, explaining the absence of MPER AA variants among all known naturally occurring HIV-1 viral sequences. Furthermore, those broadly neutralization antibodies directed against the HIV-1 MPER exploit the tandem joint architecture involving helix capping, thereby disrupting hinge function.
人类免疫缺陷病毒1型（HIV-1）利用其三聚体糖蛋白160包膜（Env）蛋白介导进入人类T淋巴细胞，该蛋白由非共价结合的糖蛋白120（gp120）和糖蛋白41（gp41）亚基组成。一种简便的病毒融合机制弥补了病毒颗粒上观察到的Env拷贝数稀少的问题，该机制包括在gp41基部（氨基酸残基662 - 683）有一个22个氨基酸的慢病毒特异性适应性结构域，称为膜近端外部区域（MPER）。我们通过核磁共振（NMR）和电子顺磁共振（EPR）表明，MPER由一对结构保守的病毒脂质包埋螺旋组成，中间由一个带有串联接头的铰链隔开，这些接头可被螺旋之间的封端残基锁定。这种设计通过结构互变促进了高效的HIV-1融合，同时提供了免疫逃逸能力。在Env位置671和674处的双丙氨酸突变（AA）破坏了两个接头，导致Env介导的细胞 - 细胞融合和半融合减弱，以及由CD4依赖型和CD4非依赖型病毒介导的病毒感染性减弱。通过对AA突变诱导的MPER构象变化进行结构分析，揭示了破坏的潜在机制。MPER中间部分更深地埋入酰基链以及交叉铰链刚体运动的消除几乎肯定会阻碍融合过程中所需的结构重排，这解释了在所有已知的天然HIV-1病毒序列中不存在MPER AA变体的原因。此外 , 那些针对HIV-1 MPER的广泛中和抗体利用了涉及螺旋封端的串联接头结构，从而破坏了铰链功能。
