MUTATIONAL ANALYSIS OF THE FUSION PEPTIDE OF THE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 - IDENTIFICATION OF CRITICAL GLYCINE RESIDUES

The ability of human immunodeficiency virus type 1 (HIV-1) to fuse its membrane with the membrane of the target cell is a function of a simi lar to 23-amino-acid amino-terminal segment of the gp41 subunit of the envelope glycoprotein complex, known as the fusion peptide. The seque nce of the fusion peptide is highly conserved among different variants of HIV-1 and is also very similar to that of HIV-2 and SIV. The fusio n peptide is very hydrophobic and has a high content of glycine and al anine residues. Representation of the fusion peptide of HIV-1 as an al pha-helix predicts that most glycine residues would be found on one fa ce of the alpha-helix. To assess the importance of the glycine residue s for the fusogenic activity of the envelope glycoprotein complex, we mutagenized each glycine residue in the fusion peptide individually to a valine residue. The mutant envelope constructs were tested for thei r ability to induce syncytia (cell/cell fusion) and to mediate infecti on (virus/cell fusion) of CD4-positive cells. The results of our analy ses show that two glycine residues (G(10) and G(13)) located within th e sequence FLGFLG in the middle of the fusion peptide are critical for syncytium formation and for the establishment of a productive infecti on, whereas other glycine residues (G(3), G(5), and G(20)) are more pe rmissive to substitutions. Mutation of each of the two phenylalanines (F-8 and F-11) of the FLGFLG sequence to valine also decreased fusion, although to a lesser extent than mutation of G(10) and G(13), These o bservations demonstrate that G(10) and G(13) are critical elements of the fusion peptide and suggest that, in addition to hydrophobicity, th e exact amino acid composition and structure of the fusion peptide are critical for function. (C) 1996 Academic Press, Inc.