Sequence similarity between the envelope surface unit (SU) glycoproteins of primate and small ruminant lentiviruses

Sequence similarity has been previously described in the transmembrane domain unit of envelope glycoproteins of primate and non-primate lentiviruses but similarity between the surface unit (SU) glycoprotein of these viruses is less clear or absent. Here we describe a consistent and significant sequence-similarity between the ovine/caprine lentivirus surface glycoprotein gp135 and the primate lentivirus gp120 in the region between variable loops V2 and V3. The biological relevance of this sequence similarity was indicated by clustering of conserved motifs in regions of structural importance in the human immunodeficiency virus type 1 gp120, conservation of cysteine residue pairs forming disulfide bonds and similar patterns of sequence variation in gp135 and gp120 between strains. The results indicate that SU glycoproteins from primate and small ruminant lentiviruses have structurally related domains.