Direct interaction of gbetagamma with a C-terminal gbetagamma-binding domain of the Ca2+ channel alpha1 subunit is responsible for channel inhibition by G protein-coupled receptors.
Several classes of voltage-gated Ca2+ channels (VGCCs) are inhibited by G proteins activated by receptors for neurotransmitters and neuromodulatory peptides. Evidence has accumulated to indicate that for non-L-type Ca2+ channels the executing arm of the activated G protein is its betagamma dimer (Gbetagamma). We report below the existence of two Gbetagamma-binding sites on the A-, B-, and E-type alpha1 subunits that form non-L-type Ca2+ channels. One, reported previously, is in loop 1 connecting transmembrane domains I and II. The second is located approximately in the middle of the ca. 600-aa-long C-terminal tails. Both Gbetagamma-binding regions also bind the Ca2+ channel beta subunit (CCbeta), which, when overexpressed, interferes with inhibition by activated G proteins. Replacement in alpha1E of loop 1 with that of the G protein-insensitive and Gbetagamma-binding-negative loop 1 of alpha1C did not abolish inhibition by G proteins, but the exchange of the alpha1E C terminus with that of alpha1C did. This and properties of alpha1E C-terminal truncations indicated that the Gbetagamma-binding site mediating the inhibition of Ca2+ channel activity is the one in the C terminus. Binding of Gbetagamma to this site was inhibited by an alpha1-binding domain of CCbeta, thus providing an explanation for the functional antagonism existing between CCbeta and G protein inhibition. The data do not support proposals that Gbetagamma inhibits alpha1 function by interacting with the site located in the loop I-II linker. These results define the molecular mechanism by which presynaptic G protein-coupled receptors inhibit neurotransmission.
Qin
N
N
Department of Anesthesiology, University of California, Los Angeles, CA 90095, USA.
Platano
D
D
Olcese
R
R
Stefani
E
E
Birnbaumer
L
L
D000818:Animals; D015220:Calcium Channels / Q000737:chemistry / Q000378:metabolism*; D002417:Cattle; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D015640:Ion Channel Gating; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction; D013552:Swine; D009435:Synaptic Transmission; D014982:Xenopus laevis
D015220:Calcium Channels; D011956:Receptors, Cell Surface; D019204:GTP-Binding Proteins