Structural investigation of the HIV-1 envelope glycoprotein gp160 cleavage site, 2: Relevance of an N-terminal helix.

Proteolytic activation of the HIV-1 envelope glycoprotein gp160 is selectively performed by the proprotein convertase furin at the C-terminus of the sequence R508-E-K-R511 (site 1), in spite of the presence of another consensus sequence, Lys500-Ala-Lys-Arg503 (site 2). On the basis of the soln. structural anal. of the synthetic peptide P498, spanning the gp160 sequence Pro498-Gly516, we previously suggested a possible role of an N-terminal helix in regulating the exposure and accessibility of the gp160 physiol. cleavage site, enclosed in a loop. Here we report on the activity and conformation of the 23-residue peptide h-REKR, designed to exhibit a large N-terminal helix, followed by the gp160 native sequence, Arg508-Gly516. H-REKR is digested by furin with high efficiency, comparable to the full native p498. CD analyses, in mixts. from pure water to 98% trifluoroethanol, outline a significant content of helical structure in the peptide conformation. The mol. model obtained from NMR data collected in trifluoroethanol/water, by means of DYANA and AMBER simulations, indeed has helical structure on a large N-terminal segment. Such a long helix does not seem to affect the loop conformation of the C-terminal site 1-contg. sequence, which exhibits the same proton chem. shifts already obsd. for the full native p498.