(Journal Article): 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.
 
Qin N, Platano D, Olcese R, Stefani E, Birnbaumer L
 
IN: Proc Natl Acad Sci U S A 1997; 94(16):8866-8871
Impact Factor(s) of Proc Natl Acad Sci U S A: 10.452 (2004), 10.272 (2003), 10.7 (2002), 10.896 (2001)

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ABSTRACT: 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.

TYPE OF PUBLICATION: Original article

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