Mutations of nonconserved residues within the calcium channel alpha(1)-interaction domain inhibit beta-subunit potentiation

作者：Gonzalez Gutierrez Giovanni; Miranda Laferte Erick; Naranjo David; Hidalgo Patricia; Neely Alan^*

来源：Journal of General Physiology, 2008, 132(3): 383-395.

DOI：10.1085/jgp.200709901

Voltage-dependent calcium channels consist of a pore-forming subunit (Ca-V alpha(1)) that includes all the molecular determinants of a voltage-gated channel, and several accessory subunits. The ancillary beta-subunit (Ca-V beta) is a potent activator of voltage-dependent calcium channels, but the mechanisms and structural bases of this regulation remain elusive. Ca-V beta binds reversibly to a conserved consensus sequence in Ca-V alpha(1), the alpha(1)-interaction domain (AID), which forms an alpha-helix when complexed with Ca-V beta. Conserved aromatic residues face to one side of the helix and strongly interact with a hydrophobic pocket on Ca-V beta. Here, we studied the effect of mutating residues located opposite to the AID-Ca-V beta contact surface in Ca(V)1.2. Substitution of AID-exposed residues by the corresponding amino acids present in other Ca-V alpha(1) subunits (E462R, K465N, D469S, and Q473K) hinders Ca-V beta's ability to increase ionic-current to charge-movement ratio (I/Q) without changing the apparent affinity for Ca-V beta. At the single channel level, these Ca(V)1.2 mutants coexpressed with Ca-V beta 2a visit high open probability mode less frequently than wildtype channels. On the other hand, Ca(V)1.2 carrying either a mutation in the conserved tryptophan residue (W470S, which impairs Ca-V beta binding), or a deletion of the whole AID sequence, does not exhibit Ca-V beta-induced increase in I/Q. In addition, we observed a shift in the voltage dependence of activation by +12 mV in the AID-deleted channel in the absence of Ca-V beta, suggesting a direct participation of these residues in the modulation of channel activation. Our results show that Ca-V beta-dependent potentiation arises primarily from changes in the modal gating behavior. We envision that Ca-V beta spatially reorients AID residues that influence the channel gate. These findings provide a new framework for understanding modulation of VDCC gating by Ca-V beta.

• 出版日期2008-9