Guanylyl cyclase C is an N-linked glycoprotein receptor that accounts for multiple heat-stable enterotoxin-binding proteins in the intestine.
Guanylyl cyclase C (GC-C) is a newly discovered receptor found in the intestine, and possibly in other epithelia, that binds bacterial heat-stable enterotoxins (STa). The receptor has now been stably expressed in human embryonic 293 cells, which do not normally contain the receptor. Cyclic GMP concentrations are elevated 40-fold in response to 1 microM STa, and membranes obtained from the overproducing cells contain GC-C activity that can be stimulated about 9-fold by STa alone and an additional 1.4- to 2-fold by a combination of ATP and STa. The ATP effect does not appear to be due to enzyme activation, but instead to protection of GC-C against inactivation. Antibody raised against the carboxyl-terminal sequence of GC-C identified two major proteins (M(r) 140,000 and 160,000) in 293 cells expressing GC-C. Both proteins bound to wheat germ lectin-Sepharose, and N-glycosidase F treatment converted both forms to a single M(r) 120,000 protein, the size predicted from amino acid composition. The addition of high concentrations of tunicamycin to 293-GC-C cells also reduced the M(r) to 120,000, indicating that GC-C is an N-linked glycoprotein. When rat intestinal membranes or 293-GC-C cells were cross-linked with 125I-labeled STa, the major 125I-labeled protein complexes had M(r) ranging between 45,000 and 80,000. On immunoblots of rat intestinal membranes treated with a reducing agent, 3 major proteins of M(r) 65,000, 85,000, and 140,000 were specifically recognized by a GC-C antibody. However, under nonreducing conditions one major GC-C related protein appeared at a higher position (M(r) 230,000). Its mobility was reduced in the presence of STa, similar to rCG-C expressed in 293 cells. These data indicate that at least part of the lower M(r) STa-binding proteins found in intestinal extracts represent proteolytic products of GC-C.
Vaandrager
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Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas 75235.
Schulz
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De Jonge
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Garbers
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D000255:Adenosine Triphosphate / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism / Q000494:pharmacology; D002460:Cell Line; D006152:Cyclic GMP / Q000378:metabolism; D004247:DNA / Q000235:genetics; D004355:Drug Stability; D004622:Embryo, Mammalian; D004768:Enterotoxins / Q000378:metabolism / Q000494:pharmacology; D029968:Escherichia coli Proteins; D015870:Gene Expression; D006031:Glycosylation; D006162:Guanylate Cyclase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D007668:Kidney; D008871:Microvilli / Q000378:metabolism; D008969:Molecular Sequence Data; D051381:Rats; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D018000:Receptors, Peptide; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D011956:Receptors, Cell Surface; D018000:Receptors, Peptide; D011994:Recombinant Proteins; C034151:heat stable toxin (E coli); D000255:Adenosine Triphosphate; D004247:DNA; D006162:Guanylate Cyclase; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D006152:Cyclic GMP