Heat-stable enterotoxin receptor/guanylyl cyclase C is an oligomer consisting of functionally distinct subunits, which are non-covalently linked in the intestine

• Published in: The Journal of biological chemistry 1994-06, Vol.269 (23), p.16409-16415
• Main Authors: VAANDRAGER, A. B, VAN DER WIEL, E, HOM, M. L, LUTHJENS, L. H, DE JONGE, H. R
• Format: Article
• Language: English
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Bacterial Toxins - metabolism; Biological and medical sciences; Cell receptors; Cell structures and functions; Cross-Linking Reagents; Electrons; Enterotoxins - metabolism; Enzyme Activation; Enzymes and enzyme inhibitors; Escherichia coli Proteins; Fundamental and applied biological sciences. Psychology; Guanylate Cyclase - chemistry; Guanylate Cyclase - radiation effects; Intestines - enzymology; Lyases; Male; Microvilli - enzymology; Miscellaneous; Models, Biological; Molecular and cellular biology; Molecular Weight; Protein Conformation; Rats; Rats, Wistar; Receptors, Enterotoxin; Receptors, Guanylate Cyclase-Coupled; Receptors, Peptide - chemistry; Receptors, Peptide - radiation effects; Ultracentrifugation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(17)34022-x

Guanylyl cyclase (GC) C is a heat-stable enterotoxin (STa) receptor with a monomeric M(r) of approximately 140,000. We calculated from its hydrodynamic parameters that an active GC-C complex has a M(r) of 393,000, suggesting that GC-C is a trimer under native conditions. Both trimeric and dimeric GC-C complexes were detected by 125I-STa binding and SDS-polyacrylamide gel electrophoresis under non-reducing conditions. The GC activity and STa binding from intestinal brush border membranes comigrated in gel filtration and velocity sedimentation with recombinant GC-C. However, 125I-STa cross-linking demonstrated that STa receptors with molecular masses of 52 and 74 kDa are non-covalently attached to GC in the intestine. Radiation inactivation revealed different functional sizes for basal GC activity, STa-stimulated GC activity, and STa binding (59, 210-240, and 32-52 kDa, respectively). At low radiation doses, basal GC activity was stimulated, suggesting that GC-C is inhibited by a relatively large, probably internal structure. These results suggest that STa may activate GC-C by promoting monomer-monomer interaction (internal "dimerization") within a homotrimeric GC-C complex, and that GC-C is proteolytically modified in the brush border membrane but retains its function.