The function of coreceptor as a basis for the kinetic dissection of HIV type 1 envelope protein-mediated cell fusion.
The function of HIV-1 HXB2 envelope (Env) glycoprotein (gp) was investigated by surface plasmon resonance and fluorescence imaging techniques. Strikingly, it was found that gp120 shedding requires the presence of the X4 coreceptor. A similar coreceptor requirement was observed for the membrane mixing and the Env recruitment on the cell surface. However, exposure and membrane penetration of the fusion peptide do not require X4 and occur within the first minute after incubation of Env with CD4 and/or X4. Analogously X4 was not required but enhanced binding of the fusion inhibitor. In contrast, bundle formation of the gp41 ectodomain, as monitored by NC-1, was accelerated by the presence of X4. The kinetics of these key post-Env binding events as determined in real time by fluorescence microscopic imaging, coupled with the differential coreceptor requirement, led to the proposition that gp120 shedding, which takes place from 1 to 10 min after engagement of receptor and coreceptor to Env, is a primary function of the coreceptor. The shedding of the surface subunits is needed for the subsequent processes including hemifusion, full fusion, and Env recruitment. The temporal order of these fusogenic steps allows construction of a refined model on the Env-mediated cell fusion event.
Chien
Miao-Ping
MP
Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, Republic of China.
Jiang
Shibo
S
Chang
Ding-Kwo
DK
D000818:Animals; D015704:CD4 Antigens / Q000276:immunology / Q000378:metabolism; D002459:Cell Fusion; D015700:HIV Envelope Protein gp41 / Q000378:metabolism; D015497:HIV-1 / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D051379:Mice; D041681:NIH 3T3 Cells; D010446:Peptide Fragments / Q000378:metabolism; D019718:Receptors, CXCR4 / Q000378:metabolism*; D020349:Surface Plasmon Resonance; D054299:env Gene Products, Human Immunodeficiency Virus / Q000378:metabolism*
D015704:CD4 Antigens; D015700:HIV Envelope Protein gp41; D010446:Peptide Fragments; D019718:Receptors, CXCR4; C435505:T-649 peptide; D054299:env Gene Products, Human Immunodeficiency Virus