Synthesis and structure elucidation of kappa-casein (45-87) - A two dimensional nuclear magnetic resonance study

We have shown that 44 amino acid residues N-terminal segment of kappa-casei n exhibits considerable a-helical structure. This prompted us to investigat e the structures of the remaining segments of kappa-casein. Thus, in this s tudy the chemical synthesis and structure elucidation of the peptide 45-87 amino acid residues of kappa-casein is reported. The peptide was assembled using solid phase peptide synthesis methodology on pam resin, cleaved via H F, freeze dried and, after purification, characterised by mass spectrometry (observed m/z 4929; calculated mit 4929.83). The amino acid sequence of th e peptide is: CKPVALINNQFLPYPYYAKPAAVRSPAQILQWQVLSNTVPAKA Its structure elucidation has been carried out using circular dichroism (CD ) and nuclear magnetic resonance (NMR) techniques. CD spectrum of the pepti de shows it to be a random structure in water but in 30% trifluoroethanol t he peptide exhibits considerable structure. The 1D and 2D NMR spectra corro borated the results of CD. The structure elucidation of the peptide using T OCSY and NOESY NMR techniques will be discussed.