Difference in binding-site architecture of the serum-type and liver-type mannose-binding proteins

The carbohydrate-recognition domains (CRDs) of the serum-type and the liver-type mannose-binding proteins (MBPs) from rat display different binding characteristics toward mannose-rich oligosaccharides derived from N-glycosides, despite the overall similarity in their binding site architecture, oligomeric status and actual binding specificity at the monosaccharide level. We found that the liver-type MBP CRD of rat (MBP-C) bound methyl glycosides of certain mannobioses and -trioses, which are part of the mannose-rich N-glycoside, more tightly than methyl α-mannopyranoside. In contrast, the serum-type MBP CRD of rat (MBP-A) bound all the methyl glycosides of manno-oligosaccharide and methyl α-mannopyranoside with similar affinities. The mannobiose and -triose most strongly bound to MBP-C CRD were Manα(1-2)Manα-OMe and Manα (1-2)Manα(1-6)Manα-OMe, respectively. From these and other data, we postulate that the binding site of MBP-C has an extended area of interaction, probably the size of a mannotriose, while MBP-A interacts essentially with one mannose residue. Abbreviations: MBP, mannose-binding protein; CRD, carbohydrate-recognition domain; BSA, bovine serum albumin; TFA-ah, 6-(trifluoroacetyl)aminohexyl; PNP, p-nitrophenyl This revised version was published online in November 2006 with corrections to the Cover Date.