Analysis of the N‐linked oligosaccharides of human C1s using electrospray ionisation mass spectrometry

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Abstract
Information on the structures of the oligosaccharides linked to Asn residues 159 and 391 of the human complement protease Cs was obtained using mass spectrometric and monosaccharide analyses. Asn159 is linked to a complex‐type biantennary, bisialylated oligosaccharide NeuAc2 Gal2 GlcNAc4 Man3 (molecular mass = 2206 ± 1). Asn391 is occupied by either a biantennary, bisialylated oligosaccharide, or a triantennary, trisialylated species NeuAc3 Gal3 GlcNAc5 Man3 (molecular mass = 2861 ± 1), or a fucosylated triantennary, trisialylated species NeuAc3 Ga13 GIcNAc5 Man3 Fucl (molecular mass = 3007 ± 1), in relative proportions of approximately 1:1:1. The carbohydrate heterogeneity at Asn391 gives rise to three major types of Cs molecules of molecular masses 79,318 ± 8 (A), 79,971 ± 8 (B), and 80,131 ± 8 (C), with an average mass of 79,807 ± 8. A minor modification, yielding an extra mass of 132 ± 2, is also detected within positions 1–153.