GP-3, a newly characterized glycoprotein on the inner surface of the zymogen granule membrane, undergoes regulated secretion

• Published in: The Journal of biological chemistry Vol. 269; no. 12; pp. 9099 - 9104
• Main Authors: WAGNER, A. C. C, WISHART, M. J, MULDERS, S. M, BLEVINS, P. M, ANDREWS, P. C, LOWE, A. W, WILLIAMS, J. A
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 25-03-1994
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; Cholecystokinin - pharmacology; Cytoplasmic Granules - chemistry; Fundamental and applied biological sciences. Psychology; Glycoproteins; Immunologic Techniques; Intracellular Membranes - metabolism; Lipase - metabolism; Male; Membrane Glycoproteins - chemistry; Membrane Glycoproteins - metabolism; Molecular Weight; Pancreatic Juice - chemistry; Phosphatidylinositol Diacylglycerol-Lyase; Phosphoinositide Phospholipase C; Phosphoric Diester Hydrolases - metabolism; Proteins; Rats; Rats, Sprague-Dawley; Solubility; Zymogen granule; Rat; Enzyme; Secretion; Rodentia; Triacylglycerol lipase; Esterases; Glycoproteins; Carboxylic ester hydrolases; Internal membrane; Vertebrata; Mammalia; Hydrolases; Carbohydrate chain; Localization; Pancreas
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(17)37082-5

We have recently reported the cloning of the rat zymogen granule membrane glycoprotein GP-3 and the related pancreatic secretory
lipase (Wishart, M. J., Andrews, P. C., Nichols, R., Blevins, G. T., Logsdon, C.D., and Williams, J. A. (1993) J. Biol. Chem.
268, 10303-10311). Specific antipeptide antibodies were generated against both GP-3 and secretory lipase and used for the
biochemical and physiological characterization of GP-3. Western blotting confirmed that GP-3 was found exclusively in zymogen
granule membranes and was absent from zymogen granule content which contains the majority of secretory lipase. Extraction
of zymogen granule membranes with Triton X-114 showed GP-3 to be significantly more hydrophobic than lipase. The GP-3 amino
acid sequence contains one potential N-linked glycosylation site at Asn-336. The loss of concanavalin A labeling after both
chemical deglycosylation with trifluoromethanesulfonic acid and enzymatic deglycosylation with N-glycanase showed GP-3 to
possess a small N-linked oligosaccharide side chain. Digestion of intact and permeabilized zymogen granules with the nonspecific
protease Pronase localized GP-3 to the inner surface of zymogen granule membranes. Since GP-3 is resident on the inner surface
of the zymogen granule membrane, it should appear on the outer cellular surface after exocytosis. Although membrane attachment
of GP-3 was resistant to treatment with phosphatidylinositol-specific phospholipase C, we observed that GP-3 is released into
the pancreatic juice and that secretion of GP-3 was greatly enhanced by cholecystokinin.