Cell Line and Site Specific Comparative Analysis of the N-Linked Oligosaccharides on Human ICAM-1des454−532 by Electrospray Ionization Mass Spectrometry

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Abstract
Sialylated oligosaccharide structures were determined by the technique of electrospray ionization mass spectroscopy at seven of eight N-linked glycosylation sites of recombinant human ICAM-1des454-532 [tICAM(453)] purified from the tissue culture fluid of Chinese hamster ovary, human embryonic kidney, and mouse myeloma cell lines. The number of structures at each site depended on the cell line and ranged from 8 to 34. N-Glycolyneuraminic acid, a human oncofetal antigen, was found at all sites of all three cell line derived forms of tICAM(453). Tetraantennary complex structures containing one and/or two galactose-beta 1,4 N-acetylglucosamine repeats, characteristic of membrane bound proteins, were found on soluble tICAM(453) primarily at Asn-379. Asn-379, located between the D4 and D5 domains, is believed to be located close to the membrane surface in membrane bound ICAM-1. It has been proposed that the extent of N-linked glycosylation at Asn-240 and Asn-269 in the third domain of ICAM-1 may regulate the binding avidity of ICAM-1 to Mac-1 [Diamond, M. S., Staunton, D. E., Marlin, S. D., & Springer, T. A. (1991) Cell 65, 961-971]. In the present study the tICAM(453) Asn-269 site was found to contain predominantly one oligosaccharide structure that is conserved in all three cell lines. On the other hand, the Asn-240 site was found to contain cell line dependent oligosaccharide structural heterogeneity particularly in the degree of sialylation.