Recent crystal structure analysis of HIV-1 gp41 revealed that two domains (N- and C-domains) on gp41 play an important role in mediating membrane fusion and HIV-1 entry. The experimental evidence that gp41 by N-domain bound the potential receptor protein P45 could help to understand the mechanism of HIV entry. A recombinant soluble gp41 (rsgp41: Env aa539-684) could bind to P45 in the affinity capillary electrophoresis analysis and the surface plasmon resonance assay. In a blockade assay, peptide P1 (Env aa583-599) could inhibit interaction between rsgp41 and P45, while a control peptide could not. Direct binding of rsgp41, rgp41DP (aa567-648), P1 peptide and (P1)(2) peptide [(aa586-596)(2)] to P45 was examined in an ELISA assay. Rsgp41 bound the potential receptor protein P45 strongly, while rgp41DP and P1 as well as (P1)(2) could all weakly bind to P45, indicating that gp41 by N-domain weakly binds P45 and the region RILAVERYLKD located in the N-domain is defined as the binding site for P45 binding.
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