Dual regulation by G proteins of agonist‐dependent phosphorylation of muscarinic acetylcholine receptors

Abstract

Muscarinic acetylcholine receptors purified from porcine atrium were phosphorylated, depending on the presence of agonists, by a protein kinase partially purified from porcine brain, which had similar properties to the )%adrenergic receptor kinase. GTP-binding regulatory proteins (Go) had dual effects on the phosphorylation of muscarinic receptors, i.e. stimulation at lower concentrations and inhibition at higher concentrations. The stimulatory effect was reproduced with the By subunit of Go and the inhibitory effect with the combination of the a and By subunits.

Location of agonist‐dependent‐phosphorylation sites in the third intracellular loop of muscarinic acetylcholine receptors (m2 subtype)

“…The mAChR kinase is the same as or very similar to the P-adrenergic-receptor kinase, and has been shown to phosphorylate rhodopsin and P-adrenergic receptor as well as mAChR (Haga and Haga, 1992;Kameyama et al, 1993). Similarly the P-adrenergic-receptor kinase is known to phosphorylate rhodopsin (Benovic et a1.1986), mAChR (Kwatra et al, 1989), and a,-adrenergic receptor (Benovic et al, 1987b) as well as P-adrenergic receptor.…”

“…The P y subunits of G protein were prepared as described (Haga and Haga, 1992). mAChR kinase was purified from porcine cerebrum by a modification of the procedure used for purification of P-adrenergic-receptor kinase (Benovic et al, 1987a), as described previously .…”

“…The fusion protein was found to be phosphorylated by the mAChR kinase and this phosphorylation was inhibited by heparin, a specific inhibitor of the mAChR kinase (Haga and Haga, 1992) and P-adrenergicreceptor kinase (Benovic et al, 1989b;Fig. 8).…”

Calcium‐bound recoverin targets rhodopsin kinase to membranes to inhibit rhodopsin phosphorylation

“…1 (open bars), Ca2+/ recoverin had no effect on the rate of light-dependent rhodopsin phosphorylation by I]ARK which is another member of the G protein-coupled receptor kinases. Unlike RK, I]ARK is stimulated by GI]7 [17][18][19], but the GI]T stimulated I]ARK activity was also unaffected by the addition of Ca2+/recoverin ( Fig. 1, stippled bars).…”

Selective Reduction in A2 Adenosine Receptor Desensitization Following Antisense‐Induced Suppression of G Protein‐Coupled Receptor Kinase 2 Expression

“…and E.K., unpublished data). Both GRK2 and 3 are partly cytosolic proteins that migrate to the membrane on receptor activation, in part owing to their ability to bind free G ␤␥ subunits, which promotes membrane association and thus assists in kinase-receptor targeting (Haga and Haga, 1992;Pitcher et al, 1992;Koch et al, 1993). DNM GRK2 reduces the agonist-induced desensitization of GPCRs, presumably by competing with endogenous GRKs for binding to both receptor and free G ␤␥ subunits (Kong et al, 1994).…”