Structural features of a peptide corresponding to human kappa-casein residues 84-101 by H-1-nuclear magnetic resonance spectroscopy

The peptide Val-Arg-Arg-Pro-Asn-Leu-His-Pro-Ser-Phe-Ile-Ala-Ile-Pro-Pro-Lys -Lys-Ile, which corresponds to residues 84-101 of human kappa-casein: has b een synthesized and its conformation preferences determined by H-1-nuclear magnetic resonance spectroscopy in dimethyl sulphoxide. The peptide adopted a largely extended chain conformation in solution and there was evidence f or the presence of a beta-turn involving residues Pro(87)-His(90) of human kappa-casein. The presence of a turn in this position would make the physio logically significant Arg(85) residue of human kappa-casein (which is equiv alent to Arg(97) in bovine kappa-casein) unavailable for interaction with A sp(249) Of bovine chymosin, and may partly explain why human kappa-casein i s hydrolysed more slowly than its bovine counterpart by bovine chymosin.