Molecular endpoints of Ca2+/calmodulin- and voltage-dependent inactivation of Ca(v)1.3 channels.
Ca(2+)/calmodulin- and voltage-dependent inactivation (CDI and VDI) comprise vital prototypes of Ca(2+) channel modulation, rich with biological consequences. Although the events initiating CDI and VDI are known, their downstream mechanisms have eluded consensus. Competing proposals include hinged-lid occlusion of channels, selectivity filter collapse, and allosteric inhibition of the activation gate. Here, novel theory predicts that perturbations of channel activation should alter inactivation in distinctive ways, depending on which hypothesis holds true. Thus, we systematically mutate the activation gate, formed by all S6 segments within Ca(V)1.3. These channels feature robust baseline CDI, and the resulting mutant library exhibits significant diversity of activation, CDI, and VDI. For CDI, a clear and previously unreported pattern emerges: activation-enhancing mutations proportionately weaken inactivation. This outcome substantiates an allosteric CDI mechanism. For VDI, the data implicate a "hinged lid-shield" mechanism, similar to a hinged-lid process, with a previously unrecognized feature. Namely, we detect a "shield" in Ca(V)1.3 channels that is specialized to repel lid closure. These findings reveal long-sought downstream mechanisms of inactivation and may furnish a framework for the understanding of Ca(2+) channelopathies involving S6 mutations.
Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. mtadross@gmail.com
Michael R
MR
Tadross
Manu
M
Ben Johny
David T
DT
Yue
D000465:Algorithms; D000595:Amino Acid Sequence; D000818:Animals; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology*; D015640:Ion Channel Gating; D008564:Membrane Potentials / Q000502:physiology*; D008961:Models, Structural; D008969:Molecular Sequence Data; D017354:Point Mutation; D011487:Protein Conformation; D051381:Rats; D015398:Signal Transduction / Q000502:physiology; D040681:Structural Homology, Protein; D013329:Structure-Activity Relationship
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002147:Calmodulin; C093712:Cacna1d protein, rat