A 1H-NMR study of the casein phosphopeptide alpha s1-casein(59-79)

Complete sequence-specific resonance assignments have been determined for a calcium phosphate sequestering, phosphoseryl-containing, tryptic peptide alpha s1-casein(59-79) containing the phosphorylated motif -SSSEE-. Spectra have been recorded in the presence of excess Ca2+ and at three different values of sample pH to characterize the changes in peptide conformation as calcium binds to the phosphorylated residues. The secondary structure of the peptide was characterized by sequential (i,i + 1), medium-range (i,i + 2/3/4), and long-range (i,i + 5) NOE connectivities, C alpha H chemical shifts, NH to C alpha H coupling constants and the observation of slowly exchanging amide protons. Two structured regions have been identified: residues P73 to V76 implicated in beta-turn conformations, and residues E61 to sigma 67 involved in a loop-type structure.