Molecular modelling investigation of wild-type and the R528H mutated segment IIS4 of human L-type voltage-gated calcium channels.
A molecular modelling study was performed in order to investigate the pathologically modified properties of L-type voltage-gated calcium channels caused by the arginine-to-histidine mutation at position 528 (R528H) in segment IIS4. For an appropriate consideration of the ionization state the finite difference Poisson-Boltzmann method was applied to compute the apparent pKa values of all titratable residues using standard conditions and an explicit lipophilic environment, respectively. Restrained molecular dynamics simulations were carried out for the alpha-helical transmembrane segments of the wild-type and the R528H mutant to explore their conformational behaviour. While both structures showed almost the same side-chain flexibility around the conserved residues, only the mutant partially formed a hydrogen bond from H528 to R531 during dynamics simulations. This local interaction not only causes a lower mobility of the directly involved residues but also leads to a global distortion of all positively charged amino acids of the mutant. Mostly affected is the side-chain of R534 that is shifted about 61 degrees closer to R531 and about 5 A in the direction of the cytoplasm. Subsequent examination of the molecular characteristics of this putative voltage sensor of the channel revealed considerable variations with regard to hydrogen bonding and electronic properties. Most obvious are the dramatic loss of a strong positive molecular electrostatic potential and the reduced hydrogen donor activities around position 528 of the mutant. How these results may be interpreted in relation to an enhanced inactivation rate is discussed, considering earlier findings at homologous voltage-gated potassium and sodium channels.
Schleifer
K J
KJ
Institute for Pharmaceutical Chemistry, Heinrich-Heine-Universität Düsseldorf, Germany. kjs@pharm.uni-duesseldorf.de
Höltje
H D
HD
D000595:Amino Acid Sequence; D000818:Animals; D015220:Calcium Channels / Q000737:chemistry* / Q000235:genetics; D020746:Calcium Channels, L-Type; D006801:Humans; D006860:Hydrogen Bonding; D015640:Ion Channel Gating; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
D015220:Calcium Channels; D020746:Calcium Channels, L-Type