D. Riitano et al., A MUTATION CHANGES LIGAND SELECTIVITY AND TRANSMEMBRANE SIGNALING PREFERENCE OF THE NEUROKININ-1 RECEPTOR, The Journal of biological chemistry, 272(12), 1997, pp. 7646-7655
studied the biochemical properties of a genetically engineered neuroki
nin-1 receptor (NK(1)R) in which two residues lying on the extracellul
ar edge of the fourth transmembrane domain were replaced by equivalent
ly located elements of the neurokinin-2 receptor (G166C, Y167F NK(1)R
mutant), The mutation produced two effects, The first is enhancement o
f the apparent binding affinity for heterologous tachykinins (substanc
e K and neurokinin B) and for N- or C-terminal modified analogues of s
ubstance P, but not for substance P itself, its full-length analogues,
and several peptide and nonpeptide antagonists, Only two antagonists,
as exceptions, were found 60 exhibit a diminished affinity for the mu
tant receptor. The second effect is a shift in NK(1)R preference for d
istinct G protein-mediated signaling pathways, NK(1)R mediated phospho
inositide hydrolysis was enhanced both in transiently and permanently
transfected cells, while stimulation of cAMP accumulation did not chan
ge in transient expression experiments and was reduced in permanently
expressing cells. The effect of the mutation on ligand affinity was no
t related to any obvious structural commonality, nor to the selectivit
y for different neurokinin receptors or the agonistic/antagonistic nat
ure of the ligand, However, all ligands responding to the mutation app
ear to share the ability to induce phosphoinositide signaling more eff
iciently than cAMP responses when binding to NK(1)R. We suggest that t
he mutation shifts the internal equilibria of different functional for
ms of NK(1)R. A theoretical analysis according to a multistate alloste
ric model suggests that the link between binding and biological change
s can result from altered stability constants of substates in the conf
ormational space of the receptor.