J. Biol. Chem., Vol. 261, Issue 14, 6423-6428, 05, 1986
Functional interaction of purified muscarinic receptors with purified inhibitory guanine nucleotide regulatory proteins reconstituted in phospholipid vesicles
H Kurose, T Katada, T Haga, K Haga, A Ichiyama and M Ui
The GTP binding regulatory protein (Ni involved in adenylate cyclase
inhibition was purified from rat brain and reconstituted, together with
muscarinic cholinergic receptors purified from porcine brain, into
phospholipid vesicles. Guanosine 5'-O-(3-[35S]thio)-triphosphate ([35S]GTP
gamma S) binding and GTP hydrolyzing activities of reconstituted Ni were
stimulated by the addition of a muscarinic agonist, carbachol. The effect
of carbachol was to increase the Vmax values of these activities, but the
Km values were also increased slightly in most cases. Carbachol bound to
vesicles with the same order of magnitude of Km as that for stimulation of
GTPase. The affinity of this binding was reduced by GTP gamma S, indicating
that the high- affinity receptor-Ni complex was formed in a GTP-dependent
manner in reconstituted vesicles. Incubation of Ni with NAD and
islet-activating protein (IAP), pertussis toxin, caused ADP-ribosylation of
the alpha- subunit of Ni. The criteria for the receptor-Ni interaction,
i.e. carbachol stimulation of the activities of Ni and the GTP gamma S
effect on carbachol binding, were no longer observed, when this IAP-
treated Ni, instead of the nontreated Ni, was reconstituted into vesicles,
though there was no difference between IAP-treated and nontreated Ni in
their basal activities observable without carbachol. No, the protein with a
character very similar to Ni in rat brain, was also coupled to muscarinic
receptors when they were reconstituted into vesicles under the same
conditions. Thus, GTP-binding proteins serving as the substrate of
IAP-catalyzed ADP-ribosylation are capable of interaction functionally with
muscarinic receptors in phospholipid vesicles.