Molecular characterization of Limulus polyphemus C-reactive protein.

The N-linked oligosacchafides of C-reactive protein (CRP) from the arachnid Limulus polyphemus, the horseshoe crab, were characterized after their release by hydrazinolysis, re-N-acetylation, and reduction with NaB³H₄. High-voltage paper electrophoresis of the reduced oligosaccharides revealed only neutral species. Gel-permeation chromatography on Bio-Gel P4 yielded five tractions. The oligosaccharide fractions were further fractionated using high-voltage borate paper electrophoresis and Dionex BioLC ion-exchange chromatography. The oligosaccharides were structurally characterized by sequential exoglycosidase digestion, fragmentation by acetolysis and methylation analysis. Three major structures were found, of which two were the biantennary oligomannose type with compositions Man₅GlcNAc₂ (B-1), Man₄GlcNAc₂ (C-3) and one was the monoantennary structure Man₃GlcNAc₂ (D-1). The biantennary oligomannose structures B-1 and C-3 contained the structural unit Manα6Manα6R. This unusual arrangement of mannose linkages suggests a biosynthetic pathway in Limulus which differs from that reposed in mammals, plants and the parasitic protozoa. [ABSTRACT FROM AUTHOR]