ENGINEERING MAGNESIUM SELECTIVITY IN THE HELIX-LOOP-HELIX CALCIUM-BINDING MOTIF

Engineering magnesium selectivity into the helix-loop-helix (hlh) cati on binding site is relatively unstudied in the calmodulin superfamily of calcium-regulated proteins, which include parvalbumin, oncomodulin, troponin C, calbindin, and calmodulin. Studies using a 33-residue syn thetic peptide model of the hlh cation binding motif have indicated th at magnesium will induce structural change in those peptide motifs con taining three or four acid residues in chelating positions with a sing le-acid-pair on the Z-axis. Decreasing the cation binding cavity size in Z-axis acid-paired motifs through replacement of chelating residues in the +Z or -X metal ion coordinating positions in the loop region b y glutamic acid has been successful in decreasing the calcium ion affi nity. The same changes did not create or enhance magnesium binding in the 33-residue model hlh cation binding motif. (C) 1995 Academic Press , Inc.