Dimerization of the class A G protein-coupled neurotensin receptor NTS1 alters G protein interaction.
G protein-coupled receptors (GPCRs) have been found as monomers but also as dimers or higher-order oligomers in cells. The relevance of the monomeric or dimeric receptor state for G protein activation is currently under debate for class A rhodopsin-like GPCRs. Clarification of this issue requires the availability of well defined receptor preparations as monomers or dimers and an assessment of their ligand-binding and G protein-coupling properties. We show by pharmacological and hydrodynamic experiments that purified neurotensin receptor NTS1, a class A GPCR, dimerizes in detergent solution in a concentration-dependent manner, with an apparent affinity in the low nanomolar range. At low receptor concentrations, NTS1 binds the agonist neurotensin with a Hill slope of approximately 1; at higher receptor concentrations, neurotensin binding displays positive cooperativity with a Hill slope of approximately 2. NTS1 monomers activate G alpha q beta(1)gamma(2), whereas receptor dimers catalyze nucleotide exchange with lower affinity. Our results demonstrate that NTS1 dimerization per se is not a prerequisite for G protein activation.
White
Jim F
JF
Membrane Protein Structure and Function Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA.
Grodnitzky
Justin
J
Louis
John M
JM
Trinh
Loc B
LB
Shiloach
Joseph
J
Gutierrez
Joanne
J
Northup
John K
JK
Grisshammer
Reinhard
R
D001667:Binding, Competitive / Q000528:radiation effects; D002850:Chromatography, Gel; D019281:Dimerization; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism*; D006801:Humans; D008027:Light; D008970:Molecular Weight; D009496:Neurotensin / Q000378:metabolism; D011485:Protein Binding / Q000528:radiation effects; D018028:Receptors, Neurotensin / Q000302:isolation & purification / Q000378:metabolism*; D012031:Refractometry; D012542:Scattering, Radiation; D013329:Structure-Activity Relationship; D014466:Ultraviolet Rays
D018028:Receptors, Neurotensin; D009496:Neurotensin; D043802:GTP-Binding Protein alpha Subunits, Gq-G11