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.
Gaggelli
E
E
Department of Chemistry and NMR Center, University of Siena, Via A. Moro, Siena 53100, Italy.
D'Amelio
N
N
Gaggelli
N
N
Valensin
G
G
D003300:Copper / Q000737:chemistry*; D004723:Endorphins / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D010446:Peptide Fragments / Q000737:chemistry*; D011392:Proline / Q000737:chemistry*; D011487:Protein Conformation; D012996:Solutions; D013237:Stereoisomerism; D013816:Thermodynamics
D004723:Endorphins; D010446:Peptide Fragments; D012996:Solutions; C043158:beta-casomorphin 4; D003300:Copper; D011392:Proline