COLLECTIN-43 IS A SERUM LECTIN WITH A DISTINCT PATTERN OF CARBOHYDRATE-RECOGNITION

Collectin-43 (CL-43) is a C-type serum lectin and a member of the coll ectin family of soluble proteins that are effector molecules in innate immunity. We have investigated the binding specificity of CL-43 using as model systems a panel of structurally defined oligosaccharides in the form of neoglycolipids, and several glycoproteins derived from the complement glycoprotein C3 during activation of the complement cascad e. A specificity is revealed towards fucose as part of the Le(a) oligo saccharide sequence, and towards mannose as found on high mannose-type chains. These are features shared with other serum collectins, conglu tinin and mannan-binding proteins; a major difference is the lack of d etectable binding by CL-43 to N-glycosidic oligosaccharides terminatin g in N-acetylglucosamine. CL-43 has a unique pattern of reactivity tow ards high mannose-type oligosaccharides on the two glycosylation sites of C3 and derived glycoproteins: it binds to C3c (not bound by conglu tinin and mannan-binding protein) but not to hydrolysed C3 [C3(H2O)], C3b or iC3b immobilized on microwells (all bound by conglutinin but no t by mannan-binding protein). When these glycoproteins are sodium dode cyl sulphate (SDS)-treated and immobilized on nitrocellulose, CL-43 (b ut not conglutinin nor mannan-binding protein) binds strongly to C3(H2 O), iC3b and C3c. The salient conclusions are, first, that there are r emarkable positive or negative effects of carrier protein on oligosacc haride presentation and these differ for the individual collectins. Se cond, the different though partially overlapping binding patterns amon g the collectins may be important for their function as circulating ef fector molecules with broad surveillance capabilities.