The molecular basis for T-type Ca2+ channel inhibition by G protein β2γ2 subunits

Abstract

Gβy, a ubiquitous second messenger, relays external signals from G protein-coupled receptors to networks of intracellular effectors, including voltage-dependent calcium channels. Unlike high-voltage-activated Ca 2+ channels, the inhibition of low-voltage-activated Ca2+ channels is subtype-dependent and mediated selectively by Gβ2- containing dimers. Yet, the molecular basis for this exquisite selectivity remains unknown. Here, we used pure recombinant Gβγ subunits to establish that the Gβ2γ2 dimer can selectively reconstitute the inhibition of α1H channels in isolated membrane patches. This inhibition is the result of a reduction in channel open probability that is not accompanied by a change in channel expression or an alteration in active-channel gating. By exchanging residues between the active Gβ2 subunit and the inactive Gβ1 subunit, we identified a cluster of amino acids that functionally distinguish Gβ2 from other Gβ subunits. These amino acids on the β-torus identify a region that is distinct from those regions that contact the Gα subunit or other effectors. © 2006 by The National Academy of Sciences of the USA.