title: Identification of N-terminal receptor activity-modifying protein residues important for calcitonin gene-related peptide, adrenomedullin, and amylin receptor function.
abstract: Calcitonin-family receptors comprise calcitonin receptor-like receptor (CL) or calcitonin receptor and receptor activity-modifying protein (RAMP) pairings. Calcitonin gene-related peptide (CGRP) receptors are CL/RAMP1, whereas adrenomedullin (AM) receptors are CL/RAMP2 (AM1 receptor) or CL/RAMP3 (AM2 receptor). Amylin (Amy) receptors are RAMP hetero-oligomers with the calcitonin receptor (AMY1, AMY2, and AMY3, respectively). How RAMPs change G protein-coupled receptor pharmacology is not fully understood. We exploited sequence differences between RAMP1 and RAMP3 to identify individual residues capable of altering receptor pharmacology. Alignment of human RAMPs revealed eight residues that are conserved in RAMP2 and RAMP3 but are different in RAMP1. We hypothesized that residues in RAMP2 and RAMP3, but not RAMP1, are responsible for making CL/RAMP2 and CL/RAMP3 AM receptors. Using site-directed mutagenesis, we introduced individual RAMP3 residues into RAMP1 and vice versa in these eight positions. Mutant or wild-type RAMPs were transfected into Cos7 cells with CL or the insert-negative form of the calcitonin receptor [CT(a)]. Agonist-stimulated cAMP production and cell-surface expression of constructs were measured. Position 74 in RAMP1 and RAMP3 was critical for determining AM potency and affinity, and Phe93 in RAMP1 was an important contributor to alphaCGRP potency at CGRP receptors. Mutant RAMP/CT(a) receptor complexes displayed different phenotypes. It is noteworthy that RAMP1 S103N and W74E mutations led to enhanced rAmy potency, probably related to increased cell-surface expression of these complexes. This differs from the effect on CL-based receptors where expression was unchanged. Targeted substitution has emphasized the importance of position 74 in RAMP1/RAMP3 as a key determinant of AM pharmacology.
authors.affiliation: School of Biological Sciences, University of Auckland, Symonds Street, Auckland, New Zealand.
authors.forename: Tao
authors.initials: T
authors.lastname: Qi
authors.forename: George
authors.initials: G
authors.lastname: Christopoulos
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Bailey
authors.forename: Arthur
authors.initials: A
authors.lastname: Christopoulos
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Sexton
authors.forename: Debbie L
authors.initials: DL
authors.lastname: Hay
mesh_terms: D053607:Adrenomedullin / Q000378:metabolism*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D015740:Calcitonin Gene-Related Peptide / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D005576:Colforsin / Q000494:pharmacology; D017124:Conserved Sequence; D000242:Cyclic AMP / Q000032:analysis; D006388:Hemagglutinins / Q000737:chemistry; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D020128:Inhibitory Concentration 50; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals; D058262:Receptor Activity-Modifying Protein 1; D058263:Receptor Activity-Modifying Protein 2; D058264:Receptor Activity-Modifying Protein 3; D058261:Receptor Activity-Modifying Proteins; D058287:Receptors, Islet Amyloid Polypeptide; D018000:Receptors, Peptide / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014162:Transfection
chemical_list: D006388:Hemagglutinins; D007074:Immunoglobulin G; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D021382:Protein Sorting Signals; C545502:RAMP1 protein, human; C545503:RAMP2 protein, human; C545504:RAMP3 protein, human; D058262:Receptor Activity-Modifying Protein 1; D058263:Receptor Activity-Modifying Protein 2; D058264:Receptor Activity-Modifying Protein 3; D058261:Receptor Activity-Modifying Proteins; D058287:Receptors, Islet Amyloid Polypeptide; D018000:Receptors, Peptide; D053607:Adrenomedullin; D005576:Colforsin; D000242:Cyclic AMP; D015740:Calcitonin Gene-Related Peptide