Probing ligand-induced conformational isomerization in the viral envelope glycoprotein GP120 by optical biosensor kinetic analysis.

6. ZHANG W, CANZIANI G, WYATT R, SODROSKI J, SWEET R, KWONG P, HENDRICKSON W, CHAIKEN I.

Washington, DC

Conferencia; ASBMB; 1998

ASBMB

Binding of the T-cell antigen CD4 to human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120 has been reported to induce conformational rearrangements in the envelope complex that facilitate recognition of the CCR5 coreceptor and consequent viral entry into cells. To better understand the mechanism of virus docking and cell fusion, we developed a three-component gp120-CD4-17b optical biosensor assay to visualize the CD4-induced conformational change of gp120 as seen through envelope binding to a neutralizing human antibody, 17b, which binds to epitopes overlapping the CCR5 binding site. The 17b Fab fragment was immobilized on a dextran sensor surface, and kinetics of gp120 binding were evaluated by both global and linear transformation analyses. Adding soluble CD4 (sCD4) increased the association rate of full-length JR-FL gp120 by 25-fold. This change is consistent with greater exposure of the 17b binding epitope on gp120 when CD4 is bound and correlates with CD4- induced conformational changes in gp120 leading to higher affinity binding to coreceptor. A smaller enhancement of 17b binding by sCD4 was observed with a mutant of gp120, ¢JR-FL protein, which lacks V1 and V2 variable loops and N- and C-termini. Biosensor results for JR-FL and ¢JR-FL argue that CD4-induced conformational changes in the equilibrium state of gp120 lead both to movement of V1/V2 loops and to conformational rearrangement in the gp120 core structure and that both of these lead to greater exposure of the coreceptor-binding epitope in gp120.