Dimer of the precursor of HIV-2 envelope glycoprotein

#This invention relates to viral proteins and glycoproteins, to compositions containing these proteins, to methods of preparing the proteins, and to their use in detecting viral infection.

#The etiological agent of acquired immunodeficiency syndrome (AIDS) is the retrovirus referred to as human immunodeficiency virus (HIV) (Montagnier et al., 1984). To date, two related but distinct viruses, HIV-1 and HIV-2, have been identified (Barre-Sinoussi et al., 1983; Popovic et al., 1984; Levy et al., 1984; Wain-Hobson et al., 1985a; Clavel et al., 1986a; Brun-Vezinet et al., 1987; Guyader et al., 1987). HIV-2 is closely related to simian immunodeficiency virus (SIV), which causes an AIDS-like disease in macaques (Daniel et al, 1985; Sonigo et al., 1985; Chakrabarti et al., 1987).

#HIV-1, HIV-2, and SIV show all the features of retrovirus family members (Wain-Hobson et al., 1985b; Montagnier and Alizon, 1987; Guyader et al., 1987; Chakrabarti et al., 1987). Their proviral genomes contain two long terminal repeats (LTRs) and three essential genes required for virus replication encoding the viral internal structural proteins (gag), the reverse transcriptase (pol), and the envelope glycoproteins (env) of the virus. In addition to these genes, both HIVs and SIV contain additional genes encoding the proteins which regulate viral expression (tat and art/trs) and three other genes encoding proteins of unknown function (Q or sor, F or 3'orf, and R). The only notable difference in the genetic organizations of HIV-1, HIV-2, and SIV resides in the open reading frame referred to as X, which is absent in HIV-1.

#This invention will be described in greater detail by referring to the drawings in which:

#FIG. 1A is a fluorograph in which high molecular weight proteins of HIV-1 and HIV-2 are compared after electrophoresis in a polyacrylamide SDS-gel;

#FIG. 1B depicts the result of electrophoresis of HIV-2 glycoproteins in an acrylamide gel;

#As a result of this invention, the processing of HIV-2 envelope glycoproteins has now been characterized. Four glycoproteins referred to as gp300, gp140, gp125, and gp36 are synthesized in HIV-2 infected cells. The gp125 and gp36 correspond to the external and transmembrane glycoproteins of HIV-2 virion, whereas gp300 and gp140 are only detectable in infected cells. The gp300 is a dimeric form of gp140, which is the immature precursor of HIV-2 envelope glycoprotein. This dimer is very stable since it resists ionic and non-ionic detergents high salt, 4M urea, and reducing agents. However, the dimer can be dissociated in acidic pH to yield gp140.

#Dimerization occurs in the endoplasmic reticulum after the removal of glucose residues by glucosidases I and II, and after the action of Golgi mannosidases, the dimer becomes dissociated probably due to a shift in pH of the environment in trans Golgi. Finally, proteolytic cleavage of the mature precursor occurs outside the Golgi.

#Transient dimer formation of the glycoprotein precursor seems to be an intrinsic property of the polypeptide moiety of HIV-2 envelope. This is a novelty in the mechanism of glycoprotein processing with N-linked oligosaccharide chains. It is hypothesized that conformational modifications brought about by the formation of this dimer are necessary for transport of the glycoprotein precursor to the Golgi apparatus.