Evidence that interaction between conserved residues in transmembrane helices 2, 3, and 7 are crucial for human VPAC1 receptor activation.
The VPAC(1) receptor belongs to family B of G protein-coupled receptors (GPCR-B) and is activated upon binding of the vasoactive intestinal peptide (VIP). Despite the recent determination of the structure of the N terminus of several members of this receptor family, little is known about the structure of the transmembrane (TM) region and about the molecular mechanisms leading to activation. In the present study, we designed a new structural model of the TM domain and combined it with experimental mutagenesis experiments to investigate the interaction network that governs ligand binding and receptor activation. Our results suggest that this network involves the cluster of residues Arg(188) in TM2, Gln(380) in TM7, and Asn(229) in TM3. This cluster is expected to be altered upon VIP binding, because Arg(188) has been shown previously to interact with Asp(3) of VIP. Several point mutations at positions 188, 229, and 380 were experimentally characterized and were shown to severely affect VIP binding and/or VIP-mediated cAMP production. Double mutants built from reciprocal residue exchanges exhibit strong cooperative or anticooperative effects, thereby indicating the spatial proximity of residues Arg(188), Gln(380), and Asn(229). Because these residues are highly conserved in the GPCR-B family, they can moreover be expected to have a general role in mediating function.
Chugunov
Anton O
AO
Unité de Bioinformatique Génomique et Structurale, Université Libre de Bruxelles, Brussels, Belgium.
Simms
John
J
Poyner
David R
DR
Dehouck
Yves
Y
Rooman
Marianne
M
Gilis
Dimitri
D
Langer
Ingrid
I
D000818:Animals; D001216:Asparagine / Q000235:genetics / Q000378:metabolism; D022082:Cellular Structures / Q000378:metabolism; D006224:Cricetinae; D006801:Humans; D016296:Mutagenesis; D017433:Protein Structure, Secondary / Q000235:genetics; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I / Q000235:genetics / Q000378:metabolism*; D014660:Vasoactive Intestinal Peptide / Q000235:genetics / Q000378:metabolism
D043562:Receptors, G-Protein-Coupled; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I; D014660:Vasoactive Intestinal Peptide; D001216:Asparagine