THE ROLE OF CALCIUM AND N-LINKED GLYCANS IN THE OLIGOMERIZATION AND CARBOHYDRATE-BINDING PROPERTIES OF HUMAN-IMMUNODEFICIENCY-VIRUS EXTERNAL ENVELOPE GLYCOPROTEIN

Envelope glycoproteins of human immunodeficiency virus (gp120 and gp41 ) occur as oligomers. Here, we show by gel filtration analysis that gp 120 oligomerization in vitro is calcium- and temperature-dependent. Re combinant gp120 (rgp120) species were recovered as monomers at 20 degr ees C in the absence of calcium, but as tetramers at 37 degrees C in 1 0 mM CaCl2. Under the latter condition, N-glycanase-deglycosylated rgp 120 formed hexamers. Relative to intact rgp120, which has been reporte d to display carbohydrate-binding properties for N-acetyl-beta-D-gluco saminyl and mannosyl residues, deglycosylation enhanced rgp120 specifi c binding to mannose-divinylsulfone-agarose, para-aminophenyl-beta-D-G lcNAc-agarose and fetuin-agarose matrices. Taken together, these resul ts rule out the role of homologous lectin-carbohydrate interactions vi a N-linked glycans in the rgp120 oligomerization, even though its lect in properties may also be calcium-dependent. Deglycosylation may unmas k domains of rgp120 polypeptide backbone that independently play a rol e either in rgp120 lectin activity or in calcium-dependent oligomeriza tion.