Sequence‐specific assignments of downfield‐shifted amide proton resonances of calmodulin Use of two‐dimensional NMR analysis of its tryptic fragments

Two‐dimensional NMR methods were applied to assign the extremely downfield‐shifted amide‐proton resonances in the 500‐MHz 1 H‐NMR spectra of the NH 2 ‐terminal fragment of residues 1–75 of calmodulin. The low‐field resonances of the 1 H‐NMR spectra of intact calmodulin were assigned to specific amino acid residues by comparison with spectra of the tryptic fragments of residues 1–75 and 78–148, in both the Ca 2+ ‐free and Ca 2+ ‐bound states. The hydrogen bonding of glycine residues connecting the two amino acid residues at the Z and − Y positions in the octahedral Ca 2+ coordination site was investigated. The Gly 134 in site IV showed a different property from the other glycines, 25, 61 and 98, involved in sites I, II and III, respectively.