M. Nakano et al., STRUCTURE AND FUNCTION OF THE N-LINKED CARBOHYDRATE CHAINS OF PIG ZONA-PELLUCIDA GLYCOPROTEINS, Journal of Reproduction and Fertility, 1996, pp. 25-34
The N-linked carbohydrate chain of the PZP3 glycoprotein family of pig
zona pellucida is shown by competition assay to possess sperm recepto
r activity. Structural analysis reveals that the N-linked chains compr
ise neutral and acidic complex-type chains. The tri- or tetra-antennar
y fraction in the neutral chains possesses the sperm receptor activity
, but the activity is markedly reduced compared with that of PZP3, sug
gesting that the protein moiety participates in the maintenance of pro
per orientation of the active chain. Two components in the PZP3 family
can be separated by reverse-phase HPLC after endo-beta-galactosidase
(E beta G) digestion and one of the digests, E beta G-PZP3 alpha, poss
esses the sperm receptor activity. E beta G-PZP alpha deprived of O-li
nked chains by treatment with alkali retains the activity comparable w
ith E beta G-PZP3 alpha, while E beta G-PZP3 alpha deprived of N-linke
d chains by N-glycanase digestion loses the activity. Furthermore, com
petition assay of the digests of E beta G-PZP3 alpha with lysyl-endope
ptidase indicates that the active chain is linked to Asn67 or Asn84 of
PZP3 alpha or to both residues. We conclude that sperm-egg binding in
pigs is mainly mediated by tri- or tetra-antennary, neutral, complex-
type N-linked carbohydrate chain(s) localized in the N-terminal region
of PZP3 alpha protein.