Critical amino acids responsible for conferring calcium channel characteristics are located on the surface and around beta-turn potentials of channel proteins.

Calcium ion is thought to be one of the initial signals in the process of synaptic modification. Various reports have described that the critical amino acids responsible for determining calcium permeability of ion channels are glutamic acid, glutamine, arginine, and asparagine. By using a computational method (MacPROT) distinguishing transmembrane, globular, and surface sequences of proteins, the present work predicts that the critical amino acids exist within surface regions of the proteins. Furthermore, occurrence of beta-turn probabilities can be predicted around these critical residues by the protein conformational prediction method of Chou and Fasman. The results suggest that the critical amino acids exist at hydrophilic spaces or canals of membranous channel proteins and that the redirection potential of the protein chain induced by the turn structures provides the conformational change requisite for the ion selectivity and gating (opening/closing) of the channels.