Analysis of the microheterogeneity of the IgA1 hinge glycopeptide having multiple O-linked oligosaccharides by capillary electrophoresis

It was found that the self-aggregation of IgA1 was closely connected with t he glycoform of a mucin-type sugar chain on its hinge portion. In this repo rt, normal human serum IgA1 was separated into two subfractions by a jacali n column. The elution condition, 25 mM galactose, used here was similar to that reported for the glycoprotein with a single mucin-type sugar chain per molecule. The IgA1 eluted under this condition was substantially the monom eric form. In contrast, the remaining IgA1 eluted from the column with 0.8 M galactose was substantially the aggregated form. An analytical method for the microheterogeneity of the IgA1 hinge glycopeptide (HGP33) was develope d to determine the difference between these IgA1 fractions by capillary ele ctrophoresis (CE). Native HGP33 from both IgA1 fractions was separated into peaks 1-11, depending on their glycoforms. Because the sialic acid-rich co mponent migrated slowly on CE, the 25 mM fraction was abundant in the siali c acid-rich components (peaks 7-11), but the 0.8 M fraction was abundant in the sialic acid-poor components (peaks 1-4). Comparison of the number of s ugar chains per hinge peptide indicated that the 25 mM fraction was relativ ely well glycosylated. Thus, application of CE analysis to the HGP33 indica ted that the monomeric IgA1 was composed of a relatively complete molecule with respect to the glycoform rather than the aggregated IgA1. (C) 2001 Aca demic Press.