Structural and functional analysis of the HIV gp41 core containing an Ile573 to Thr substitution: implications for membrane fusion.
The envelope glycoprotein of HIV-1 consists of the surface subunit gp120 and the transmembrane subunit gp41. Binding of gp120 to target cell receptors induces a conformational change in gp41, which then mediates the fusion of viral and cellular membranes. A buried isoleucine (Ile573) in a central trimeric coiled coil within the fusion-active gp41 ectodomain core is thought to favor this conformational activation. The role of Ile573 in determining the structure and function of the gp120-gp41 complex was investigated by mutating this residue to threonine, a nonconservative substitution in HIV-1 that occurs naturally in SIV. While the introduction of Thr573 markedly destabilized the gp41 core, the three-dimensional structure of the mutant trimer of hairpins was very similar to that of the wild-type molecule. A new hydrogen-bonding interaction between the buried Thr573 and Thr569 residues appears to allow formation of the trimer-of-hairpins structure at physiological temperature. The mutant envelope glycoprotein expressed in 293T cells and incorporated within pseudotyped virions displayed only a moderate reduction in syncytium-inducing capacity and virus infectivity, respectively. Our results demonstrate that the proper folding of the gp41 core underlies the membrane fusion properties of the gp120-gp41 complex. An understanding of the gp41 activation process may suggest novel strategies for vaccine and antiviral drug development.
Liu
J
J
Department of Biochemistry, Weill Medical College of Cornell University, New York, New York 10021, USA.
Shu
W
W
Fagan
M B
MB
Nunberg
J H
JH
Lu
M
M
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics*; D002460:Cell Line; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D015700:HIV Envelope Protein gp41 / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D015497:HIV-1 / Q000235:genetics* / Q000472:pathogenicity; D006801:Humans; D007532:Isoleucine / Q000235:genetics*; D008561:Membrane Fusion / Q000235:genetics*; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D020449:Repetitive Sequences, Amino Acid; D013329:Structure-Activity Relationship; D013912:Threonine / Q000235:genetics*; D014162:Transfection; D014407:Tumor Cells, Cultured; D014771:Virion / Q000235:genetics / Q000472:pathogenicity; D014774:Virulence
D015700:HIV Envelope Protein gp41; D007532:Isoleucine; D013912:Threonine