Structure/function--HIV/SIV EnvelopeTransmembrane Gp41

背景：人类（HIV）和相关猿猴（SIV）免疫缺陷病毒的包膜糖蛋白被合成为gp160前体，gp160前体被加工成两个非共价相关的糖蛋白：gp120和gp41。gp120通过结合位于宿主细胞表面的细胞受体CD4和趋化因子辅助受体介导病毒进入宿主细胞。这种结合诱导跨膜gp41的构象变化，促进病毒和宿主膜之间的膜融合。在分子水平上对这些过程的理解可能会导致抑制HIV感染的直接手段。HIV pg41和密切相关的SIV gp41是高度糖基化的跨膜蛋白。位于病毒膜外表面的外域区域通过n端融合域直接介导膜融合事件。gp41外畴的核磁共振和x射线结构都得到了求解。两种方法确定的结构是一个棒状三聚体，包括三个平行的n端α -螺旋在中心组装成一个线圈，三个反平行的c端α -螺旋在外部包装，高度柔性的环连接内外螺旋。

Background: The envelope glycoprotein of the human (HIV) and related simian (SIV) immunodeficiency virus are synthesized as gp160 precursors which are processed into two non-covalently associated glycoproteins: gp120 and gp41. The gp120 mediates viral entry into the host cell by binding to the cellular receptor CD4 and a chemokine coreceptor, both of which are located on the host cell surface. This binding induces conformational changes in the transmembrane gp41, which facilitates membrane fusion between the viral and host membranes. An understanding of these processes at the molecular level may lead to a direct means of inhibiting HIV infection. HIV pg41, and the closely related SIV gp41, are heavily glycosylated transmembrane proteins. The ectodomain region, located on the outer surface of the viral membrane directly mediates membrane fusion events via an N-terminal fusion domain. Both the NMR and X-ray structures of the gp41 ectodomain have been solved. The structure determined by both methods is a rod-like trimer comprising three parallel N-terminal alpha-helices assembled as a coiled-coil in the center with three antiparallel C-terminal alpha-helices packed on the outside with highly flexible loops connecting the inner and outer helices. Results: To gain further insight into gp41 function we have expressed in bacteria regions of the protein for which there is currently no structural information, namely, the extremely hydrophobic N-terminal fusion peptide, the transmembrane region and the long cytoplasmic domain. The proteins produced are being studied by new NMR techniques (A. Bax) designed for the structural analysis of membrane proteins and peptides. The structure of a membrane associated region of the cytoplasmic domain was previously determined and the structure of the N-terminal fusion domain has now been determined. We are preparing site-specific mutants of the helical N-terminal fusion domain which abrogate the fusion process in order to correlate activity and structure. In other studies we have examined mutants of the HIV gp41 ectodomain which are resistant to the new class of peptide inhibitors targeted against membrane fusion. We have shown that the resistance mutations increase the thermodynamic stability of the gp41 ectodomain and these results provides new insight into the potential mechanism of resistance. Significance and future direction: More detailed structure determinations of the whole gp41 protein will allow a more rational approach to the design of novel peptide inhibitors.