Natural variation in the amino acid sequence around the HIV type 1 glycoprotein 160 cleavage site and its effect on cleavability, subunit association, and membrane fusion

To assess the natural variation of the structure of the cleavage site as we ll as the N-terminal region of gp41 for the cytopathogenicity of HIV-1, syn cytium-inducing (SI) and non-syncytium-inducing (NSI) virus isolates were o btained from HIV-1-infected patients. In addition, the coreceptor usage of the isolates was determined by infection of primary macrophages and PM-1 ce lls. DNA sequences encoding the C-terminal 41 amino acid residues of gp120 and the 64 amino acid N-terminal residues of gp41 were amplified by the pol ymerase chain reaction and inserted into the Env expression vector pNLA1. W hen transfected into HeLa-T4(+) cells, all the recombinant plasmids, includ ing those with inserts from NSI isolates, led to the formation of processed glycoprotein and to syncytium formation. One construct displayed significa nt lowered fusion capacity and had an amino acid exchange in the first posi tion of the gp41 N terminus (gp41, 512A-->S) leading to a decreased associa tion of the SU and TM subunits. Four constructs derived from two isolates o f the same patient showed an unusual gp41 N terminus (gp41, 514G-->P) and a slightly diminished fusion capacity due to a decreased cleavability. This indicates that the major determinants for the SI and NSI phenotypes are not located around the gp160 cleavage site and that the N terminus of gp41 pla ys a minor role in the processing and fusion capacity of wild-type HIV-1 is olates.