IDENTIFICATION OF CRITICAL AMINO-ACIDS INVOLVED IN ALPHA(1)-BETA INTERACTION IN VOLTAGE-DEPENDENT CA2+ CHANNELS

In voltage-dependent Ca2+ channels, the alpha(1) and beta subunits int eract via two cytoplasmic regions defined as the Alpha Interaction Dom ain (AID) and Beta Interaction Domain (BID). Several novel amino acids for that interaction have now been mapped in both domains by point mu tations. It was found that three of the nine amino acids in AID and fo ur of the eight BID amino acids tested mere essential for the interact ion. Whereas the important AID amino acids mere clustered around five residues, the important BID residues were more widely distributed with in a larger 16 amino acid sequence. The affinity of the AID(A) GST fus ion protein for the four interacting beta(1b) BID mutants was not sign ificantly altered compared with the wild-type beta(1b) despite the dos e localization of mutated residues to disruptive BID amino acids. Expr ession of these interactive beta mutants with the full-length alpha(1A ) subunit only slightly modified the stimulation efficiency when compa red with the wild-type beta(1b) subunit. Our data suggest that non-dis ruptive BID sequence alterations do not dramatically affect the beta s ubunit-induced current stimulation.