title: Secondary structures in beta-casein peptide 1-42: a two dimensional nuclear magnetic resonance study.
abstract: Two dimensional NMR spectroscopy was used to study the structure of a peptide composed of the N-terminal 42 amino acid residues of beta-casein. The peptide was obtained by enzymic cleavage using endoproteinase Asp-N. Complete sequence-specific 1H NMR assignment was performed for the peptide at three Ca2+ concentrations (0, 22 and 37 mM). The NMR results show that the peptide was highly flexible and adopted multiple conformations. No stable secondary structures were present; however, the peptide had some regions with non-random structure. The region between residues Leu16 and Asn27 adopted conformations with an increased contribution of alpha-helical structure, a so-called nascent helix. Two regions, Glu11-SerP15 and Lys29-Phe33 showed an increased population of conformations with extended structures. Addition of Ca2+ induced chemical shift changes for the backbone amide protons, especially around the phosphoserine region and around the suggested alpha-helical structure, indicating that the addition of Ca2+ stabilized the structure already present in the apo form of the peptide.
authors: Department of Food Technology, University of Lund, Sweden.
authors: N M
authors: NM
authors: Wahlgren
authors: P
authors: P
authors: Dejmek
authors: T
authors: T
authors: Drakenberg
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002364:Caseins / Q000737:chemistry* / Q000302:isolation & purification; D002417:Cattle; D005260:Female; D009682:Magnetic Resonance Spectroscopy; D008892:Milk / Q000737:chemistry; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000302:isolation & purification; D017433:Protein Structure, Secondary
chemical_list: D002364:Caseins; D010446:Peptide Fragments; C091551:beta-casein (1-42)