Molecular architecture of native HIV-1 gp120 trimers

Abstract

The envelope glycoproteins (Env) of human and simian immunodeficiency viruses (HIV and SIV, respectively) mediate virus binding to the cell surface receptor CD4 on target cells to initiate infection 1 . Env is a heterodimer of a transmembrane glycoprotein (gp41) and a surface glycoprotein (gp120), and forms trimers on the surface of the viral membrane. Using cryo-electron tomography combined with three-dimensional image classification and averaging, we report the threedimensional structures of trimeric Env displayed on native HIV-1 in the unliganded state, in complex with the broadly neutralizing antibody b12 and in a ternary complex with CD4 and the 17b antibody. By fitting the known crystal structures 2,3 of the monomeric gp120 core in the b12-and CD4/17b-bound conformations into the density maps derived by electron tomography, we derive molecular models for the native HIV-1 gp120 trimer in unliganded and CD4-bound states. We demonstrate that CD4 binding results in a major reorganization of the Env trimer, causing an outward rotation and displacement of each gp120 monomer. This appears to be coupled with a rearrangement of the gp41 region along the central axis of the trimer, leading to closer contact between the viral and target cell membranes. Our findings elucidate the structure and conformational changes of trimeric HIV-1 gp120 relevant to antibody neutralization and attachment to target cells. It is estimated that over 33 million individuals are at present infected with HIV (http://www.unaids.org). The development of an effective vaccine is therefore a challenge of fundamental medical interest. It has been widely recognized that a better understanding of the structure of trimeric Env in its various conformational states is likely to be an important element in the overall strategy for vaccine development 4 . Although X-ray crystallographic methods have led to atomic models for HIV-1 gp120 monomers complexed to antibodies in the presence and absence of CD4 (refs 2 , 3, 5 ), determination of the structures of intact trimers on native viruses has nevertheless remained elusive. Theoretical models for the structure of the trimer that take into account constraints determined from biochemical and mutagenesis studies of monomeric gp120 (refs 6 , 7 ) have been advanced, but the advent of electron tomographic methods 8 provides a unique opportunity for direct experimental determination of the structure of the intact trimer on the virus in its native state. Here we report structural analysis of native HIV-1 Env using alignment and classification procedures that take into account the missing wedge that arises from the limited angular range used for data collection in electron tomography. Our approach takes advantage of complexes containing monomeric gp120 for

Quaternary structures of HIV Env immunogen exhibit conformational vicissitudes and interface diminution elicited by ligand binding

“…Rotation of gp120 subunits in the liganded state could remove part of the gp120/gp41 association and contribute to its weakening, possibly further promoting gp41 N-and C-helix association through exposure of hydrophobic surfaces, facilitating quaternary arrangement for the fusion peptide to insert into the host membrane. Comparison between our native and liganded gp140 structures corroborates the Liu model of subunit rotation (11). The gp120 subunit rotates, from having its CD4BS perpendicularly accessible prior to the binding, to a location laterally exposed from gp120, such that CD4 does not sterically occlude the coreceptor binding site, thus maximizing CCR5 or CXCR4 accessibility to the bridging sheet and V3 loop.…”

Decoupling competing surface binding kinetics and reconfiguration of receptor footprint for ultrasensitive stress assays

“…The extent of biochemical detection sensitivity is therefore governed only by the technique itself. The enhanced cantilever sensitivity confirms our hypothesis that sensitive detection is strongly linked to a ligand's ability to polymerize 13 such as HIV-1 glycoprotein which forms trimeric complexes 43 .…”

Peptidomimetic inhibitors targeting the CCR5-binding site on the human immunodeficiency virus type-1 gp120 glycoprotein complexed to CD4

“…Major conformational changes occur in gp120 after docking to CD4 1 , commonly referred to as the CD4-induced (CD4i) state, which lead to the assembly of a highly conserved binding pocket for the N-terminus of CCR5. The high affinity 20 interaction of the N-terminus of CCR5 with the gp120-CD4 complex requires the unusual post-translational O-sulfation of several tyrosine residues, in particular, at positions 10 and 14 in CCR5.…”