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 lent ivirus surface unit glycoprotein (SU) gp135 and the second conserved region (C2) of the primate lentivirus gp120 which indicates a structural similari ty between gp135 and the inner proximal domain of the human immunodeficienc y virus type 1 gp120 (I. Hotzel and W. P. Cheevers, Virus Res, 69:47-54, 20 00). Here we found that the seven-amino-acid sequence of the gp120 strand b eta 25 in the C5 region, which is also part of the inner proximal domain, w as conserved in the SU of all lentiviruses in similar or identical position s 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 retroviru ses. Except for the feline immunodeficiency virus, sequences similar to the gp120 gp135 consensus for beta5 and part of the preceding strand beta4 wer e present in the SU of all lentiviruses. This motif was highly conserved am ong strains of each lentivirus and included a strictly conserved cysteine r esidue in beta4. In addition, the beta4/beta5 consensus motif was also pres ent in the conserved carboxy-terminal region of all type A and B retroviral envelope surface glycoproteins analyzed. Thus, the antiparallel beta -stra nds 5 and 25 of gp120 form an SU surface highly conserved among the lentivi ruses and at least partially conserved in the type A and B retroviral envel ope glycoproteins.