THE GLYCAN MOIETY OF HUMAN PANCREATIC LITHOSTATHINE - STRUCTURE CHARACTERIZATION AND POSSIBLE PATHOPHYSIOLOGICAL IMPLICATIONS

Lithostathine, also known as pancreatic stone protein, pancreatic thre ad protein or regenerating protein, is a glycoprotein which is normall y found in the exocrine pancreas, whereas in other tissues it appears either only under pathological conditions, such as Alzheimer's disease (brain), cancer (colon) or during regeneration (endocrine pancreas). In the latter case, it has been shown recently that it acts as a growt h factor which stimulates islet regeneration. Little is known about it s glycan moiety, which conceivably might be involved in this tissue sp ecificity and pathophysiological characteristics. Therefore we isolate d the major oligosaccharide chains of human pancreatic lithostathine a nd determined their sequences by means of NMR analysis. We obtained el even different glycoforms and we were able to determine the sequence o f seven of them. They all were from the same site of glycosylation (Th r5) and displayed the same core 2 structure: GlcNAc(beta 1-6)[Gal(beta 1-3)]GalAc alpha-. They ranged in size from 4 to 9 sugar residues. El ongation was found to proceed from a common tetrasaccharidic core: Gal (beta 1-4)GlcNAc(beta 1-6)[Gal(beta 1-3)]GalAc-ol through N-acetyllact osamine units. The non-reducing ends of some oligosaccharides carry th e antigenic determinant H, with presence of external Fuc linked only i n (alpha 1-2) to Gal. All the glycans, except one, carry a sialic acid in (alpha 2-3) linkage to Gal, with one disialylated form which displ ays a supplementary (alpha 2-6) linkage. These findings are consistent with the polymorphism of the protein, shown by means of SDS gel elect rophoresis and isoelectric focusing, either in its native form or afte r enzymic processing. Moreover, sialylation seems to protect to some e xtent the Arg11-Ile12 bond from in situ hydrolysis, thus preventing th e harmful precipitation of the C-terminal polypeptide in the pancreati c ducts.