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The guanylate kinase domain of the β-subunit of voltage-gated calcium channels suffices to modulate gating

2008; National Academy of Sciences; Volume: 105; Issue: 37 Linguagem: Inglês

10.1073/pnas.0806558105

1091-6490

Giovanni González-Gutiérrez, Erick Miranda‐Laferte, Doreen Nothmann, Silke Schmidt, Alan Neely, Patricia Hidalgo,

Cardiac electrophysiology and arrhythmias

Inactivation of voltage-gated calcium channels is crucial for the spatiotemporal coordination of calcium signals and prevention of toxic calcium buildup. Only one member of the highly conserved family of calcium channel β-subunits—Ca V β—inhibits inactivation. This unique property has been attributed to short variable regions of the protein; however, here we report that this inhibition actually is conferred by a conserved guanylate kinase (GK) domain and, moreover, that this domain alone recapitulates Ca V β-mediated modulation of channel activation. We expressed and refolded the GK domain of Ca V β 2a , the unique variant that inhibits inactivation, and of Ca V β 1b , an isoform that facilitates it. The refolded domains of both Ca V β variants were found to inhibit inactivation of Ca V 2.3 channels expressed in Xenopus laevis oocytes. These findings suggest that the GK domain endows calcium channels with a brake restraining voltage-dependent inactivation, and thus facilitation of inactivation by full-length Ca V β requires additional structural determinants to antagonize the GK effect. We found that Ca V β can switch the inactivation phenotype conferred to Ca V 2.3 from slow to fast after posttranslational modifications during channel biogenesis. Our findings provide a framework within which to understand the modulation of inactivation and a new functional map of Ca V β in which the GK domain regulates channel gating and the other conserved domain (Src homology 3) may couple calcium channels to other signaling pathways.