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

Citation
Kj. Cross et al., Cation-dependent structural features of beta-casein-(1-25), BIOCHEM J, 356, 2001, pp. 277-285
Citations number
45
Categorie Soggetti
Biochemistry & Biophysics
Journal title
BIOCHEMICAL JOURNAL
ISSN journal
02646021 → ACNP
Volume
356
Year of publication
2001
Part
1
Pages
277 - 285
Database
ISI
SICI code
0264-6021(20010515)356:<277:CSFOB>2.0.ZU;2-6
Abstract
Complete sequence-specific, proton-resonance assignments have been determin ed 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 experiment s, in the presence of excess ammonium ions, sodium ions and calcium ions, a nd of the dephosphorylated peptide in the presence of excess sodium ions. W e observed significant changes to chemical shifts for backbone and side-cha in resonances that were dependent upon the nature of the cation present. Me dium-range nuclear Overhauser effect (nOe) enhancements, characteristic of small structured regions in the peptide, were observed and also found to be cation dependent. The secondary structure of the peptide was characterized by sequential and medium-range (i, i+2/3/4, which denotes an interaction b etween residue i and residue i + 2, i+3 or i + 4 in the peptide) nOe connec tivities, and Ha chemical shifts. Four structured regions were identified i n the calcium-bound peptide: residues Arg(1) to Glu(4) were involved in a l oop-type structure, and residues Val(8) to Glu(11), Ser(P)(17) to Glu(20) a nd Glu(21) to Thr(24) were implicated in p-turn conformations. Comparison o f the patterns of medium-range nOe connectivities in beta -casein-(1-25) wi th those in alpha (s1)-casein-(59-79) suggest that the two peptides have di stinctly different conformations in the presence of calcium ions, despite h aving a high degree of sequential and functional similarity.