A H-1-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 phosphojlated residues. T he 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 co nnectivities, (CH)-H-alpha chemical shifts, NH to (CH)-H-alpha couplin g constants and the observation of slowly exchanging amide protons. Tw o structured regions have been identified: residues P73 to V76 implica ted in beta-turn conformations, and residues E61 to Sigma 67 involved in a loop-type structure.