Two proteins are cleaved from the env polyprecursor: the glycosylated outer protein gp125 and the transmembraneous protein gp36. The envelope proteins, as with other enveloped viruses, play an important role in interaction with the receptor, fusion, induction of cytopathic effects and development of humoral and cellular immune responses. The two glycopro-teins are known to be highly antigenic and immunogenic.
The env gene accumulates most of the variation and the gp125 protein exhibits more variability than the gp36 protein of HIV-2.5'6-10 Many of the cysteine residues are conserved among all the HIV strains sequenced, suggesting a common three-dimensional structure.
The large glycoprotein has diversity in the number and relative positions of the glycosylation sites in different HIV strains. This could be the result of extensive base changes in the hypervariable regions which comprise a large part of the potential N-linked glycosylation sites of the highly glycosylated gp125 protein. The hypervariable regions, consisting of 20-80 amino acid residues, are surrounded by cysteine residues, suggesting that they form loops. These variations may influence the specific immuno-genicity of the protein.11 Mapping of structures on the HIV glycoproteins indicates that by way of contrast many conserved regions may be inaccessible for antibodies in the natural configuration. The gag gene encodes for the matrix and capsid proteins. p26 elicits a strong antibody response during infection, and the presence of anti-p26 antibodies is an important tool in diagnostic tests.
The enzymatic proteins encoded by the pol gene are protease, reverse transcriptase including RNAse H activity, and endonuclease (integrase).
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