Identification of critical amino acids involved in α1‐β interaction in voltage‐dependent Ca2+ channels

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Abstract
In voltage‐dependent Ca2+ channels, the α 1 and β subunits interact via two cytoplasmic regions defined as the Alpha Interaction Domain (AID) and Beta Interaction Domain (BID). Several novel amino acids for that interaction have now been mapped in both domains by point mutations. It was found that three of the nine amino acids in AID and four of the eight BID amino acids tested were essential for the interaction. Whereas the important AID amino acids were clustered around five residues, the important BID residues were more widely distributed within a larger 16 amino acid sequence. The affinity of the AIDA GST fusion protein for the four interacting β 1b BID mutants was not significantly altered compared with the wild‐type β 1b despite the close localization of mutated residues to disruptive BID amino acids. Expression of these interactive β mutants with the full‐length α 1A subunit only slightly modified the stimulation efficiency when compared with the wild‐type β 1b subunit. Our data suggest that non‐disruptive BID sequence alterations do not dramatically affect the β subunit‐induced current stimulation.