Special Issue Article
Sachiko Kondo, Hirokazu Yag
Abstract
Immunoglobulin Y (IgY), abundant in egg yolk, is widely used as an immunochemical reagent and has been recently appreciated as a potential therapeutic tool. The Fc portion of IgY conserves an N-glycosylation site at Asn407, which is structurally equivalent to conserved glycosylation sites of other Ig classes in mammals. Despite such similarities, IgYs from chicken serum and egg yolk have been shown to be distinct glycoforms, best exemplified by the high incidence of monoglucosylated high mannose-type oligosaccharides, which are rarely found in mammalian glycoproteins. To gain further insight into the glycosylation properties of IgY, we report a comparative N-glycosylation profiling of recombinant chicken IgYs that have identical amino acid sequences in their variable regions but are expressed by different production vehicles. The N-linked oligosaccharides cleaved from these IgYs were subjected to multidimensional HPLC mapping in conjunction with mass spectrometric analyses. N-glycosylation profiles of the IgYs showed obviously different patterns depending on the production vehicle. While IgY expressed by chicken hybridoma cells retained the premature high mannose-type oligosaccharides, IgY expressed by CHO cells experienced extensive N-glycan processing and displayed high antennary oligosaccharides. Significant differences were also observed in the levels of core fucosylation and bisecting N-acetylglucosaminylation and in sialyl linkage types among the IgYs expressed by different vehicles. Despite such differences, the recombinant IgY antibodies commonly expressed considerable populations of monoglucosylated glycoforms, suggesting that this glycosylation feature is, to some extent, associated with the distinctive quaternary structure of IgY-Fc, which, at least partially, masks the Asn407 N-glycans and sequesters them from chaperone mechanisms in the endoplasmic reticulum. We suggest that the timing and efficiency of N-glycan processing and the quaternary structure formation of IgY are considerably different from those of IgE and depend on the vehicles used for recombinant IgY production, resulting in varying incidence of monoglucosylated species.