Molecular dynamics and mutational analysis of a channelopathy mutation in the IIS6 helix of Ca V 1.2

A channelopathy mutation in segment IIS6 of CaV1.4 (I745T) has been shown to cause severe visual impairment by shifting the activation and inactivation curves to more hyperpolarised voltages and slowing activation and inactivation kinetics. A similar gating phenotype is caused by the corresponding mutation, I781T, in CaV1.2 (midpoint of activation curve (V0.5) shifted to -37.7 ± 1.2 mV). We show here that wild type gating can partially be restored by a helix stabilising rescue mutation N785A. V0.5 of I781T/N785A (V0.5 = -21.5 ± 0.6 mV) was shifted back towards wild type (V0.5 = -9.9±1.1 mV). Homology models developed in our group (see accompanying article for details) were used to perform MD-simulations on wild-type and mutant channels. Systematic changes in segment IIIS6 (M1187 - F1194) and in helix IIS6 (N785-L786) were observed. The simulated structural changes in S6 segments of I781T/N785A were less pronounced than in I781T. A delicate balance between helix flexibility and stability enabling the forma...