The role of phosphate groups in the interaction of human C-reactive protein with galactan polysaccharides

Human C-reactive protein (CRP) shows binding specificities for phosphate monoesters, polycations and for several other biological macromolecules lacking these ligands. We report here that the formerly observed interaction of CRP with snail galactans, as exemplified by Helix pomatia galactan, is not due to a lectin-like carbohydrate-binding reactivity, but, instead that CRP obviously binds to phosphate groups that are minor constituents of these polysaccharides. Structural analysis of the galactan revealed that the phosphate groups are attached by a, as yet unidentified, linkage group to the carbohydrate backbone. Thus, the anti-galactan reactivity of CRP can be attributed to the protein's classical anti-phosphate/anti-phosphorylcholine specificity.