Recognition and signal transduction mechanism of Escherichia coli heat-stable enterotoxin and its receptor, guanylate cyclase C.
Guanylate cyclase C (GC-C), a member of the membrane-bound GC family, consists of an extracellular domain (ECD) and an intracellular domain, which are connected by a single-transmembrane region. GC-C is a receptor protein, i.e. specifically stimulated by the endogenous peptides guanylin, uroguanylin, lymphoguanylin, and the exogenous peptide heat-stable enterotoxin (ST(a)), secreted by pathogenic Escherichia coli and acting on the intestinal brush border membranes. The binding of these peptide ligands to the ECD of GC-C results in the synthesis of cyclic GMP in cells, which, in turn, regulates a variety of intracellular physiologic processes. As the cloning of GC-C, its physiologic functions of each domain have been vigorously investigated. The structural characterization of the ligand-binding domain of the receptor promises to provide important clues for better understanding of the mechanisms of receptor recognition and activation. Recently, structural data for each domain of membrane-bound GCs and related proteins has become available. Coupling information obtained from such work and validation of structure-function relationships of GC-C and its ligands should allow for three-dimensional mapping of their interaction site in detail. Our approach to this issue involved designing photoaffinity-labeling ST(a) analogs, capable of binding covalently to the ligand-binding region of the ECD of GC-C. The photoaffinity-labeling ligand was used to covalently label a soluble form of the recombinant ECD protein. Mass spectrometric analyses of an endoproteinase digest of the ECD revealed that the ligand specifically bound to a narrow region contained in the membrane-proximal subdomain of the ECD of GC-C. These results will enable us to identify the possible binding motifs within the ligand-binding domain by computer modeling. In this review, we summarize the available data on the recognition mechanism between ST(a) and GC-C at the molecular level.
Hasegawa
M
M
Faculty of Bioscience, Nagahama Institute of Bio-Science and Technology, Nagahama, Shiga 526-0829, Japan. m_hasegawa@nagahama-i-bio.ac.jp
Shimonishi
Y
Y
D000595:Amino Acid Sequence; D000818:Animals; D001427:Bacterial Toxins / Q000737:chemistry* / Q000378:metabolism*; D004768:Enterotoxins / Q000737:chemistry* / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005768:Gastrointestinal Hormones / Q000737:chemistry / Q000378:metabolism; D006162:Guanylate Cyclase / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D015394:Molecular Structure; D045265:Natriuretic Peptides; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D018000:Receptors, Peptide / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction
D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D005768:Gastrointestinal Hormones; D008024:Ligands; D045265:Natriuretic Peptides; D010455:Peptides; D018000:Receptors, Peptide; C034151:heat stable toxin (E coli); C072685:guanylin; D006162:Guanylate Cyclase; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled