Heat-stable enterotoxin receptor/guanylyl cyclase C is an oligomer consisting of functionally distinct subunits, which are non-covalently linked in the intestine.
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.
Vaandrager
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AB
Department of Biochemistry, Medical Faculty, Erasmus University Rotterdam, The Netherlands.
van der Wiel
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E
Hom
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ML
Luthjens
L H
LH
de Jonge
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HR
D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism*; D003432:Cross-Linking Reagents; D004583:Electrons; D004768:Enterotoxins / Q000378:metabolism*; D004789:Enzyme Activation; D029968:Escherichia coli Proteins; D006162:Guanylate Cyclase / Q000737:chemistry* / Q000528:radiation effects; D007422:Intestines / Q000201:enzymology*; D008297:Male; D008871:Microvilli / Q000201:enzymology; D008954:Models, Biological; D008970:Molecular Weight; D011487:Protein Conformation; D051381:Rats; D017208:Rats, Wistar; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D018000:Receptors, Peptide / Q000737:chemistry* / Q000528:radiation effects; D014461:Ultracentrifugation
D001427:Bacterial Toxins; D003432:Cross-Linking Reagents; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D018000:Receptors, Peptide; C034151:heat stable toxin (E coli); D006162:Guanylate Cyclase; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled