Structural Mechanism of Trimeric HIV-1 Envelope Glycoprotein Activation

PLoS Pathogens

Oleg Kuybeda¹  Guillermo Sapiro¹  David M. Schauder²  Sriram Subramaniam²  Gabriel A. Frank²  Alberto Bartesaghi²  Erin E. H. Tran²  Jacqueline L. S. Milne²  Mario J. Borgnia² 

[1] Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States of America;Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America

关键词: HIV-1;    Antibodies;    Viral structure;    CD coreceptors;    Coreceptors;    Tomography;    Cell membranes;    Viral entry;   

DOI  :  10.1371/journal.ppat.1002797

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

HIV-1 infection begins with the binding of trimeric viral envelope glycoproteins (Env) to CD4 and a co-receptor on target T-cells. Understanding how these ligands influence the structure of Env is of fundamental interest for HIV vaccine development. Using cryo-electron microscopy, we describe the contrasting structural outcomes of trimeric Env binding to soluble CD4, to the broadly neutralizing, CD4-binding site antibodies VRC01, VRC03 and b12, or to the monoclonal antibody 17b, a co-receptor mimic. Binding of trimeric HIV-1 BaL Env to either soluble CD4 or 17b alone, is sufficient to trigger formation of the open quaternary conformation of Env. In contrast, VRC01 locks Env in the closed state, while b12 binding requires a partial opening in the quaternary structure of trimeric Env. Our results show that, despite general similarities in regions of the HIV-1 gp120 polypeptide that contact CD4, VRC01, VRC03 and b12, there are important differences in quaternary structures of the complexes these ligands form on native trimeric Env, and potentially explain differences in the neutralizing breadth and potency of antibodies with similar specificities. From cryo-electron microscopic analysis at ∼9 Å resolution of a cleaved, soluble version of trimeric Env, we show that a structural signature of the open Env conformation is a three-helix motif composed of α-helical segments derived from highly conserved, non-glycosylated N-terminal regions of the gp41 trimer. The three N-terminal gp41 helices in this novel, activated Env conformation are held apart by their interactions with the rest of Env, and are less compactly packed than in the post-fusion, six-helix bundle state. These findings suggest a new structural template for designing immunogens that can elicit antibodies targeting HIV at a vulnerable, pre-entry stage.

【 授权许可】

CC BY