Title : Studies on
the carbohydrate moiety and on the biosynthesis of rat
C-reactive protein
Abstract :
- Rat C-reactive protein ( CRP ) is a pentameric glycoprotein composed of five apparently identical monomers, two of which form a disulfide-linked dimer (Rasosouli, M., Sambasivam, H., Azadi, P., Dell, A., Morris, H. R., Nagpurkar, A., Mookerjea, S., and Murray, R. K. (1992) J. Biol
- Chem
- 267, 2947-2954)
- In this study, the nature of the oligosaccharide chain of rat CRP was investigated by fast atom bombardment-mass spectrometry (FAB-MS), and general features of its biosynthetic pathway were also analyzed
- FAB-MS, electrospray-mass spectrometry, and linkage analysis demonstrated that each monomer of rat CRP contained one oligosaccharide chain , predominantly a disialylated biantennary structure , attached to Asn-128
- The biosynthesis of rat CRP was studied by immunoprecipitation of CRP synthesized in vitro and by cultured hepatocytes
- The results revealed that each monomer of rat CRP was synthesized individually as a single-chain precursor with a cleavable signal sequence
- The translocated species was sensitive to digestion by endoglycosidase H (endo H), indicating that it possessed a high mannose oligosaccharide.
- Rat CRP acquired the ability to bind to phosphorylcholine-Sepharose and to form the dimeric and oligomeric species prior to acquiring resistance to endo H. Studies using tunicamycin revealed that the N-linked oligosaccharide present in rat CRP was not required for formation of its dimeric component, oligomerization, ability to bind to phosphorylcholine, or secretion
- The non-glycosylated rat CRP , however, was still able to bind to phosphorylcholine-Sepharose and to be secreted by hepatocytes