COMPARATIVE-ANALYSIS OF THE N-GLYCANS OF RAT, MOUSE AND HUMAN THY-1 -SITE-SPECIFIC OLIGOSACCHARIDE PATTERNS OF NEURAL THY-1, A MEMBER OF THE IMMUNOGLOBULIN SUPERFAMILY

Protein structure and tissue type are known to influence glycosylation of proteins. We have previously investigated the N-glycans at each of the three glycosylation sites of the cell surface glycoprotein Thy-1 when isolated from rat brain and thymocytes. Here we report a comparat ive analysis of the site-specific N-glycosylation patterns from rat (A sn 23, 74, 98), mouse (Asn 23, 75, 99) and human (Asn 23, 60, 100) neu ral Thy-1. Despite considerable differences in amino acid sequence, th e results show a remarkable conservation of the pattern of N-glycans a t corresponding sites between the three species, as judged by chromato graphic comparisons and glycosidase susceptibility. This is particular ly marked for sites at Asn 74/75 in rat/mouse and the equivalent site at 60 in human Thy-1, as well as for sites at Asn 98/99 and 100, respe ctively. The sites at Asn 23 in rat/mouse also contained almost identi cal glycosylation patterns, but at this site human Thy-1 showed signif icantly different glycosylation patterns. These site glycosylation pat terns are discussed in relation to the likely accessibility of the oli gosaccharides for processing. It is known that within a species, the g lycosylation of Thy-1 is tissue specific; therefore, this degree of co nservation of glycosylation of Thy-1 expressed in the same tissue in d ifferent species is all the more striking, given the known variation b etween species in the amino acid sequence of Thy-1. It is therefore pr oposed that neural cells have a particular requirement for specific su rface carbohydrates and that the Thy-1 polypeptide serves as an approp riate carrier for these structures.