Cation-dependent structural features of beta-casein-(1-25)

Abstract

Complete sequence-specific, proton-resonance assignments have been determined for the calcium phosphate-stabilizing tryptic peptide beta-casein-(1-25) containing the phosphorylated sequence motif Ser(P)(17)-Ser(P)-Ser(P)-Glu-Glu(21). Spectra of the peptide have been recorded, in separate experiments, in the presence of excess ammonium ions, sodium ions and calcium ions, and of the dephosphorylated peptide in the presence of excess sodium ions. We observed significant changes to chemical shifts for backbone and side-chain resonances that were dependent upon the nature of the cation present. Medium-range nuclear Overhauser effect (nOe) enhancements, characteristic of small structured regions i..