Specific interactions of bovine and human beta-casomorphin-7 with Cu(II) ions

β-Casomorphin: A complete health perspective

β-Casomorphin-7 (BCM-7) is a heptapeptide dietary molecule derived from the digestion of the β-casein of dairy and dairy products. In this review, we have covered the extensive details about BCM and its derived peptides out of the gastrointestinal and enzymatic digestion of milk and milk products, its structure and properties, and its immunological aspects related to human health among infants and adults of both genders. We have left judgment about BCM's pros and cons to the reader by describing the details in a cyclopedic perspective. In addition, a section on the possible ways to detect BCMs from their sources using proteomics, genome-based techniques, such as PCR and aptamers, and other analytical techniques equip the reader to get an idea about the details of the diagnostics available and possible applications in future. Overall, this review will provide information to the end-users of milk and milk products to enable them to make their own decisions about BCMs.

Copper(ii) binding by fragments of α-synuclein containing M1-D2- and -H50-residues; a combined potentiometric and spectroscopic study

Stability constants and ligand donor sets of the copper(II) complexes of the NH2-29-56(L1)(AA30GKTKEGVLYV40GSKTKEGVVH50GVATVA56-NH2), NH2-M29-D30-56(L2) and Ac-M29-D30-56(L3) fragments of alpha-synuclein were determined in aqueous solution for 1 : 1 metal-to-ligand molar ratio in the pH range 2.5-10.5. The tyrosine residue in the 39th position of the alpha-synuclein fragments does not take part in the coordination of the metal ion. The potentiometric and spectroscopic data (UV-Vis, CD, EPR) show that acetylation of the amino terminal group induces significant changes in the coordination properties of the L3 fragment compared to that of the L2 peptide. When the amino group is blocked (L3) the imidazole nitrogen of the histidine residue acts as an anchoring site and at higher pH the 3N {N(Im),2N-} and 4N {N(Im),3N-} complexes are formed. The L1 peptide at physiological pH forms in equilibrium 3N {NH2,N-,CO,N(Im)} and 4N {NH2,2N-,N(Im)} complexes. For the L2 peptide the coordination of the copper(II) ions starts from the N-terminal Met residue and with increasing of pH the Asp residue in second position of amino acid sequence coordinates and stabilizes significantly the 2N complex as a result of chelation through the beta-carboxylate group. At physiological pH the 3N {NH2,N-,beta-COO-,N(Im)} coordination mode dominates. At pH above 6 the results for the L2 fragment suggest the formation of 3N and 4N complexes (in equatorial plane) and the involvement of the lateral NH2 group of Lys residue in the axial coordination of Cu(II) ion. In CD spectra sigma (epsilon-NH2-Lys) --> Cu(II) charge transfer transition is observed. The stability constants for the L2 fragment of alpha-synuclein of the 4N {NH2,2N-,N(Im)} and {NH2,3N-} complexes are higher about 1.5 and 0.7 orders of magnitude, respectively, by comparison to those of the L1 peptide. This increase may be explained by the involvement of the epsilon-NH2 group of Lys residue in the coordination sphere of metal ion.

Metal ion effects on the cis/trans isomerization equilibrium of proline in short-chain peptides: a solution NMR study

The effect of copper(II) ions on the probabilities of existence of the four detectable conformers of the tetrapeptide Tyr-Pro-Phe-Pro (beta-casomorphin 4) in [2H6]DMSO was investigated by 1H NMR spectroscopy. Integration of the Phe-NH signals provided the relative populations in the free state as tt/tc/ct/cc=28:34:29:9 at 293 K (c=cis, t=trans). Copper(II) was shown to bind to all four isomers, yielding complexes with two different structures, depending on the conformation of Pro(2). The interpretation of paramagnetic relaxation rates of Pro(2)-Halpha signals provided the corresponding isomeric probabilities in the metal-bound state as 13:36:20:31. The observed stabilization of the conformation with the lowest probability of existence (cc) may be relevant for the biological role of copper and other metal ions.

CD spectroscopic study on the speciation and solution structure of copper(II) complexes of some tripeptides in combination with potentiometric and spectrophotometric results

The combination of potentiometric, spectrophotometric and CD spectroscopic studies under the same conditions is expected to yield more reliable thermodynamic and structural information for a certain system. The matrix rank analysis of both the spectrophotometric and CD spectra series gives the necessary number of species to be taken into account in the calculations. Based on such speciation diagrams the molar spectra for individual complexes in the copper(II) Gly-Gly-Ala, Gly-Ala-Gly, Ala-Gly-Gly and Ala-Ala-Ala systems were obtained. The results allowed us to assign these spectra to two types of coordination species with the compositions CuLH(-1) and [CuLH(-2)](-). The sign and the intensity of the CD spectra are well related to the chirality and distance of the chiral center(s) in the ligand from the metal ion chromophore and the stability of the metal complexes. They are further on additive within the experimental error in both cases with respect to chiral centers: the sum of the CD spectra of the Gly-Gly-Ala, Gly-Ala-Gly and Ala-Gly-Gly complexes equals those of Ala-Ala-Ala complexes. The CD spectra strongly support the coordination also of the C-terminal part of the peptide in the CuLH(-1) complex of GGA, and even the deprotonation of the Ala peptide group instead of that belonging to Gly cannot be excluded.