Human VPAC1 receptor selectivity filter. Identification of a critical domain for restricting secretin binding.
The human VPAC1 receptor for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating peptide (PACAP) belongs to the class II family of G protein coupled receptors with seven transmembrane segments. It recognizes several VIP-related peptides and displays a very low affinity for secretin despite >70% homology between VIP and secretin. Conversely, the human secretin receptor has high affinity for secretin but low affinity for VIP. We took advantage of this reversed selectivity to identify a domain of the VPAC1 receptor responsible for selectivity toward secretin by constructing human VPAC1-secretin receptor chimeras. A first set of chimeras consisted of exchanging the entire N-terminal ectodomain or large parts of this domain. They were constructed by overlap PCR, transfected in COS-7 cells, and their ligand selectivity, expressed as the ratio of EC(50) for secretin/EC(50) for VIP (referred to as S/V), in stimulating cAMP production was measured. Two very informative chimeras respectively referred to as S144V and S123V were obtained by replacing the entire ectodomain or only the first 123 amino acids of the VPAC1 receptor by the corresponding sequences of the secretin receptor. Whereas S144V no longer discriminated between VIP and secretin (S/V = 1.2), S123V discriminated between the two peptides (S/V = 300) in the same manner as the wild-type VPAC1 receptor. The motif responsible for discrimination was determined by introducing small blocks or individual amino acids of secretin receptor in the 123-144 sequence of the S123V chimera. The data obtained from 14 new chimeras sustained that two nonadjacent pairs of amino acids, Gln(135) Thr(136) and Gly(140) Ser(141) in the C-terminal end of the N-terminal VPAC1 receptor ectodomain constitute a selective filter that strongly restricts access of secretin to the VPAC1 receptor.
Unité INSERM U410 de Neuroendocrinologie et Biologie Cellulaire Digestives, Institut National de la Santé et de la Recherche Médicale, Faculté de Médecine Xavier Bichat, 75018 Paris, France.
Kai
K
Du
Alain
A
Couvineau
Christiane
C
Rouyer-Fessard
Pascal
P
Nicole
Marc
M
Laburthe
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002522:Chlorocebus aethiops; D000242:Cyclic AMP / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D018005:Receptors, Vasoactive Intestinal Peptide / Q000737:chemistry* / Q000502:physiology*; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D012633:Secretin / Q000378:metabolism*; D012680:Sensitivity and Specificity; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology*
D010446:Peptide Fragments; D018005:Receptors, Vasoactive Intestinal Peptide; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I; D011993:Recombinant Fusion Proteins; D012633:Secretin; D014660:Vasoactive Intestinal Peptide; D000242:Cyclic AMP