Several Structural Domains Contribute to the Regulation of N-type Calcium Channel Inactivation by the β3 Subunit

Abstract

Calcium channel β subunits are essential regulatory elements of the gating properties of high voltage-activated calcium channels. Co-expression with β3 subunits typically accelerates inactivation, whereas co-expression with β4 subunits results in a slowly inactivating phenotype. Here, we have examined the molecular basis of the differential effect of these two subunits on the inactivation characteristics of Ca v2.2 + α2-δ1, N-type calcium channels by creating a series of 22 chimeric β subunits that are based on various combinations of variable and conserved regions of the parent β subunit isoforms. Our data show that replacement of the N terminus region of β4 with a corresponding 14-amino acid stretch of β 3 sequence accelerates the inactivation kinetics to levels seen with wild type β3. A similar kinetic speeding is observed by a concomitant substitution of the second conserved and variable regions, but not when these regions are substituted individually, suggesting that 1) the second variable and conserved regions cooperatively regulate N-type calcium channel inactivation and 2) that there are two redundant mechanisms that allow the β3 subunit to accelerate N-type channel inactivation. In contrast with previous reports in Cav2.1 calcium channels, deletion of the C-terminal region of Cav2.2 did not alter the regulation of the channel by wild type and chimeric β subunits. Hence, the molecular underpinnings of β subunit regulation of voltage-gated calcium channels appear to vary with calcium channel subtype.