Analysis of Human Immunodeficiency Virus 1 Envelope Proteins: Contribution of Cysteine Residues to Envelope Function
Human immunodeficiency virus type 1 (HIV-1) is the etiologic agent which causes the acquired immunodeficiency syndrome. Various HIV-1 isolates show a high level of genetic diversity. The envelope gene is the most variable (Alizon et al. 1986; Gurgo et al. 1988; Hahn et al. 1985; Srinivasan et al. 1987; Starcich et al. 1986; Willey et al. 1986); the amino acid sequence of the envelope proteins of different strains differ from each other by as much as 30% of their residues. In spite of this variation there are 21 cysteine residues in the HIV-1 envelope which are perfectly conserved in all reported isolates (Gurgo et al. 1988). Even more surprising is the conservation of the same cysteine residues within the envelope proteins of simian immunodeficiency virus (Franchini et al. 1987; Hirsch et al. 1987; Chakrabarti et al. 1987) and HIV-2 (Guyader et al. 1987), which have only 30%–40% amino acid identity with the envelope of HIV-1. This conservation of cysteine residues suggests that they are highly important to HIV-1 envelope function, most likely through the contribution of disulfide bridges to the tertiary structure of the envelope proteins.
KeywordsHuman Immunodeficiency Virus Cysteine Residue Simian Immunodeficiency Virus Envelope Protein Syncytium Formation
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