Conformational Changes of gp120 in Epitopes near the CCR5 Binding Site Are Induced by CD4 and a CD4 Miniprotein Mimetic
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- 作者：Wentao Zhang ; Gabriela Canziani ; Carmela Plugariu ; Richard Wyatt ; Joseph Sodroski ; Raymond Sweet ; Peter Kwong ; Wayne Hendrickson ; and Irwin Chaiken
- 刊名：Biochemistry
- 出版年：1999
- 出版时间：July 20, 1999
- 年：1999
- 卷：38
- 期：29
- 页码：9405 - 9416
- 全文大小：215K
- 年卷期：v.38,no.29(July 20, 1999)
- ISSN：1520-4995
文摘
Binding of the T-cell antigen CD4 to human immunodeficiency virus type 1 (HIV-1) envelopeglycoprotein gp120 has been reported to induce conformational rearrangements in the envelope complexthat facilitate recognition of the CCR5 coreceptor and consequent viral entry into cells. To better understandthe mechanism of virus docking and cell fusion, we developed a three-component gp120-CD4-17boptical biosensor assay to visualize the CD4-induced conformational change of gp120 as seen throughenvelope binding to a neutralizing human antibody, 17b, which binds to epitopes overlapping the CCR5binding site. The 17b Fab fragment was immobilized on a dextran sensor surface, and kinetics of gp120binding 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 withgreater 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 smallerenhancement of 17b binding by sCD4 was observed with a mutant of gp120, 
JR-FL protein, whichlacks V1 and V2 variable loops and N- and C-termini. Biosensor results for JR-FL and JR-FL arguethat CD4-induced conformational changes in the equilibrium state of gp120 lead both to movement ofV1/V2 loops and to conformational rearrangement in the gp120 core structure and that both of these leadto greater exposure of the coreceptor-binding epitope in gp120. A 17b binding enhancement effect onJR-FL also was observed with a 32-amino acid charybdotoxin miniprotein construct that contains anepitope predicted to mimic the Phe 43/Arg 59 region of CD4 and that competes with CD4 for gp120binding. Results with this construct argue that CD4-mimicking molecules with surrogate structural elementsfor the Phe 43/Arg 59 components of CD4 are sufficient to elicit a similar gp120 conformationalisomerization as expressed by CD4 itself.
JR-FL protein, whichlacks V1 and V2 variable loops and N- and C-termini. Biosensor results for JR-FL and JR-FL arguethat CD4-induced conformational changes in the equilibrium state of gp120 lead both to movement ofV1/V2 loops and to conformational rearrangement in the gp120 core structure and that both of these leadto greater exposure of the coreceptor-binding epitope in gp120. A 17b binding enhancement effect onJR-FL also was observed with a 32-amino acid charybdotoxin miniprotein construct that contains anepitope predicted to mimic the Phe 43/Arg 59 region of CD4 and that competes with CD4 for gp120binding. Results with this construct argue that CD4-mimicking molecules with surrogate structural elementsfor the Phe 43/Arg 59 components of CD4 are sufficient to elicit a similar gp120 conformationalisomerization as expressed by CD4 itself.