Multiple structural elements in voltage-dependent Ca2+ channels support their inhibition by G proteins.
Molecular determinants of Ca2+ channel responsiveness to inhibition by receptor-coupled G proteins were investigated in Xenopus oocytes. The inhibitory response of alpha1B (N-type) channels was much larger than alpha1A (P/Q-type) channels, while alpha1C (L-type) channels were unresponsive. Differences in both degree and speed of inhibition were accounted for by variations in inhibitor off-rate. We tested proposals that inhibitory G protein and Ca2+ channel beta subunits compete specifically at the I-II loop. G protein-mediated inhibition remained unaltered in alpha1B subunits containing a point mutation in the I-II loop segment critical for Ca2+ channel beta subunit binding, and in chimeras where the I-II loop of alpha1B was replaced with counterparts from alpha1A or alpha1c. Full interconversion between modulatory behaviors of alpha1B and alpha1A was achieved only by swapping both motif I and the C-terminus in combination. Thus, essential structural elements for G protein modulation reside in multiple Ca2+ channel domains.
Zhang
J F
JF
Department of Molecular and Cellular Physiology, Stanford University, California 94305, USA.
Ellinor
P T
PT
Aldrich
R W
RW
Tsien
R W
RW
D000818:Animals; D002121:Calcium Channel Blockers / Q000378:metabolism; D015220:Calcium Channels / Q000737:chemistry* / Q000502:physiology*; D004594:Electrophysiology; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D013997:Time Factors; D014981:Xenopus
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D011993:Recombinant Fusion Proteins; D019204:GTP-Binding Proteins