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.

*Protein Conformation, Animals, Bacterial Toxins/*metabolism, Cross-Linking Reagents, Electrons, Enterotoxins/*metabolism, Enzyme Activation, Guanylate Cyclase/*chemistry/radiation effects, Intestines/*enzymology, Male, Microvilli/enzymology, Models, Biological, Molecular Weight, Rats, Rats, Wistar, Receptors, Peptide/*chemistry/radiation effects, Ultracentrifugation
hdl.handle.net/1765/8569
Journal of Biological Chemistry
Erasmus MC: University Medical Center Rotterdam

Vaandrager, A.B, van der Wiel, E, Hom, M.L, Luthjens, L.H, & de Jonge, H.R. (1994). Heat-stable enterotoxin receptor/guanylyl cyclase C is an oligomer consisting of functionally distinct subunits, which are non-covalently linked in the intestine. Journal of Biological Chemistry. Retrieved from http://hdl.handle.net/1765/8569