A putative selectivity filter in the G-protein-coupled receptors for parathyroid hormone and secretion.
The seven transmembrane segments (TMs) of many G-protein-coupled receptors (GPCRs) are thought to form a cavity into which cognate ligands insert, leading to receptor activation. Residues lining the cavity are often essential for optimal ligand binding and/or signal transduction. The present studies evaluated whether residues lining the cavity also contribute to specificity, using GPCRs for the polypeptides parathyroid hormone (PTH) and secretin as models. These ligands display no sequence homology with one another, and neither ligand cross-reacts with the other's receptor. However, mutation of a single amino acid in the second TM of the secretin receptor to the corresponding residue in the PTH receptor (N192I) resulted in a receptor that binds and signals in response to PTH. The reciprocal mutation in the PTH receptor (I234N) likewise unmasked responsiveness to secretin. Neither mutation significantly altered the response of the receptors to their own ligands. The results suggest a model of specificity wherein TM residues near the extracellular surface of the receptor function as a selectivity filter that restricts access of inappropriate ligands to an activation site in the transmembrane cavity.
Turner
P R
PR
Endocrine Unit, Veterans Affairs Medical Center, San Francisco, California 94121, USA.
Bambino
T
T
Nissenson
R A
RA
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D000242:Cyclic AMP / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009893:Opossums; D010281:Parathyroid Hormone / Q000378:metabolism / Q000494:pharmacology*; D011487:Protein Conformation; D043562:Receptors, G-Protein-Coupled; D011964:Receptors, Gastrointestinal Hormone / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D018016:Receptors, Parathyroid Hormone / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D012633:Secretin / Q000378:metabolism / Q000494:pharmacology*; D013379:Substrate Specificity
D010281:Parathyroid Hormone; D043562:Receptors, G-Protein-Coupled; D011964:Receptors, Gastrointestinal Hormone; D018016:Receptors, Parathyroid Hormone; D011993:Recombinant Fusion Proteins; C029937:secretin receptor; D012633:Secretin; D000242:Cyclic AMP; D019204:GTP-Binding Proteins