Conservation of human immunodeficiency virus type 1 gp120 inner-domain sequences in lentivirus and type A and B retrovirus envelope surface glycoproteins.

We recently described a sequence similarity between the small ruminant lentivirus surface unit glycoprotein (SU) gp135 and the second conserved region (C2) of the primate lentivirus gp120 which indicates a structural similarity between gp135 and the inner proximal domain of the human immunodeficiency virus type 1 gp120 (I. Hötzel and W. P. Cheevers, Virus Res. 69:47-54, 2000). Here we found that the seven-amino-acid sequence of the gp120 strand beta 25 in the C5 region, which is also part of the inner proximal domain, was conserved in the SU of all lentiviruses in similar or identical positions relative to the carboxy terminus of SU. Sequences conforming to the gp135-gp120 consensus for beta-strand 5 in the C2 region, which is antiparallel to beta 25, were then sought in the SU of other lentiviruses and retroviruses. Except for the feline immunodeficiency virus, sequences similar to the gp120-gp135 consensus for beta 5 and part of the preceding strand beta 4 were present in the SU of all lentiviruses. This motif was highly conserved among strains of each lentivirus and included a strictly conserved cysteine residue in beta 4. In addition, the beta 4/beta 5 consensus motif was also present in the conserved carboxy-terminal region of all type A and B retroviral envelope surface glycoproteins analyzed. Thus, the antiparallel beta-strands 5 and 25 of gp120 form an SU surface highly conserved among the lentiviruses and at least partially conserved in the type A and B retroviral envelope glycoproteins.