To characterize putative binding sites for HIV-1 gp41 to H9 cells.Design
Based on accumulating evidence in the literature that HIV-1 can bind to cell surfaces independent of CD4, we attempted to clarify whether gp41, the transmembrane HIV-1 protein, contributes to CD4-independent binding. We therefore tested binding of gp41 to cells.Methods
Using fluorescence-activated cell-sorter analysis, we examined the binding of recombinant gp160 (rgp160) and soluble gp41 (sgp41; Env amino acids 539–684) to H9 cells, and located the putative binding site(s) of gp41 by inhibition using 16 HIV-1 Env peptides. Putative HIV-1 receptor proteins in H9 cell lysates were Western blotted and precipitated using sgp41.Results
sgp41 bound to the CD4+ H9 cells and rgp160 bound to H9 cells independent of gp120-binding sites on CD4 molecules. Two gp41 peptides (Env amino acids 591—605 and 651—665) inhibited the binding of sgp41 to H9 cells. Four bands, of 37, 40, 55 and 97 kD, were blotted in H9 cell lysates, and three bands, 40, 97 and 108 kD, were observed in the precipitation analysis using lysates of 125l-surface-labelled H9 cells and sgp41 attached to sepharose beads.Conclusions
HIV-1 gp41 contains two putative binding sites to H9 cells. These sites may be located within Env amino acids 591–605 (ERYLKDQQLLGIWGC) and 651–665 (TLLEESQNQQEKNEQ). Using two different techniques, five proteins (37, 40, 55, 97 and 108 kD) were identified in H9 lysates as possible candidates for gp41 binding.