Table 1.

Summary of expected and observed shifts in molecular masses of virion-associated, free, and SDS-denatured gp120 for each of the glycosidases tested

GlycosidaseSpecificityaMobility (kDa) of:Predicted mobility (kDa) of gp120 after complete digestion
Virion-bound gp120dFree gp120eSDS-denatured gp120f
NgFR1-GlcNAc-GlcNAc⇓Asnb 110–115806060h
N-glycosidase AR1-GlcNAc-GlcNAc⇓Asnc 12012012060i
α-Mannosidaseα1-2,3,6-linked mannose115–120115–120115NPj
eFR2-GlcNAc⇓GlcNAc-Asn12067–7260g 67k
Endoglycosidase HR3-GlcNAc⇓GlcNAc-Asn110 75–11097–85NP
Endo-β-galactosidaseR4-(GlcNAc-Galβ1)n⇓4R5 120110100NP
NeuraminidaseTerminal α2-3,6,8,9-Neu5Ac120120120105–91l
  • a The arrow indicates the site of cleavage. Asn, asparagine; Gal, galactose; Neu5Ac,N-acetylneuraminic acid; R1, high-mannose, hybrid-, or complex-form oligosaccharides; R2, high-mannose, hybrid-, or biantennary-complex-form oligosaccharides; R3, high-mannose or hybrid-form oligosaccharides; R4, Gal or Neu5Ac-Gal; R5, GlcNAc or Gal.

  • b Blocked by core fucosylation.

  • c Blocked by Neu5Ac.

  • d Mobility of pelletable, glycosidase-treated gp120 as described in the text.

  • e Mobility of immunoprecipitated, nonpelletable, glycosidase-treated gp120 as described in the text.

  • f Mobility of SDS-denatured and then glycosidase-treated gp120 as described in the text.

  • g The mobility of denatured, eF-treated SIVmac239 is greater than predicted because of NgF contamination, as described in the text.

  • h Based on the assumption that all 24 potential N-linked carbohydrates, each contributing about 2.5 kDa, are completely removed.

  • i Based on the assumption that all 24 potential N-linked carbohydrates, each contributing about 2.5 kDa, are completely removed.

  • j NP, not possible to predict.

  • k Based on the assumption that all 24 potential N-linked carbohydrates are removed by cleavage in the chitobiose core, removing about 2.2 kDa each.

  • l Based on the assumption that all 24 potential N-linked carbohydrates have two to four sialic residues, each contributing 309 Da, that are completely removed.