The molecular basis for T-type Ca2+ channel inhibition by G protein beta2gamma2 subunits.
Gbetagamma, 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 Ca(2+) channels is subtype-dependent and mediated selectively by Gbeta(2)-containing dimers. Yet, the molecular basis for this exquisite selectivity remains unknown. Here, we used pure recombinant Gbetagamma subunits to establish that the Gbeta(2)gamma(2) dimer can selectively reconstitute the inhibition of alpha(1H) 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 Gbeta(2) subunit and the inactive Gbeta(1) subunit, we identified a cluster of amino acids that functionally distinguish Gbeta(2) from other Gbeta subunits. These amino acids on the beta-torus identify a region that is distinct from those regions that contact the Galpha subunit or other effectors.
DePuy
Seth D
SD
Department of Pharmacology, University of Virginia, 1300 Jefferson Park Avenue, Charlottesville, VA 22908, USA.
Yao
Junlan
J
Hu
Changlong
C
McIntire
William
W
Bidaud
Isabelle
I
Lory
Philippe
P
Rastinejad
Fraydoon
F
Gonzalez
Carlos
C
Garrison
James C
JC
Barrett
Paula Q
PQ
D000596:Amino Acids / Q000378:metabolism; D020747:Calcium Channels, T-Type / Q000378:metabolism*; D002478:Cells, Cultured; D044387:GTP-Binding Protein beta Subunits / Q000378:metabolism*; D044388:GTP-Binding Protein gamma Subunits / Q000378:metabolism*; D006801:Humans; D015640:Ion Channel Gating; D021122:Protein Subunits / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
D000596:Amino Acids; C479952:CACNA1H protein, human; D020747:Calcium Channels, T-Type; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D021122:Protein Subunits; D011994:Recombinant Proteins