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Interaction Modes and Absolute Affinities of α-Amino Acids for Mn2+: A Comprehensive Picture

Authors

  • M. Hassan Khodabandeh,

    1. Department of Chemistry, Faculty of Sciences, Shahid Beheshti University, G.C., Evin 19839-6313, Tehran (Iran), Fax: (+98) (21) 22401765
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  • Hamid Reisi,

    1. Department of Chemistry, Faculty of Sciences, Shahid Beheshti University, G.C., Evin 19839-6313, Tehran (Iran), Fax: (+98) (21) 22401765
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  • Dr. Mehdi D. Davari,

    1. Theoretical and Computational Biophysics Department, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Goettingen (Germany)
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  • Prof. Karim Zare,

    1. Department of Chemistry, Faculty of Sciences, Shahid Beheshti University, G.C., Evin 19839-6313, Tehran (Iran), Fax: (+98) (21) 22401765
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  • Prof. Mansour Zahedi,

    Corresponding author
    1. Department of Chemistry, Faculty of Sciences, Shahid Beheshti University, G.C., Evin 19839-6313, Tehran (Iran), Fax: (+98) (21) 22401765
    • Department of Chemistry, Faculty of Sciences, Shahid Beheshti University, G.C., Evin 19839-6313, Tehran (Iran), Fax: (+98) (21) 22401765
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  • Prof. Gilles Ohanessian

    Corresponding author
    1. Laboratoire des Mécanismes Réactionnels, Département de Chimie, Ecole Polytechnique, CNRS, 91128 Palaiseau Cedex (France), Fax: (+33) (0)1 69 33 48 03
    • Laboratoire des Mécanismes Réactionnels, Département de Chimie, Ecole Polytechnique, CNRS, 91128 Palaiseau Cedex (France), Fax: (+33) (0)1 69 33 48 03
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Abstract

Manganese is involved as a cofactor in the activation of numerous enzymes as well as the oxygen-evolving complex of photosystem II. Full understanding of the role played by the Mn2+ ion requires detailed knowledge of the interaction modes and energies of manganese with its various environments, a knowledge that is far from complete. To bring detailed insight into the local interactions of Mn in metallopeptides and proteins, theoretical studies employing first-principles quantum mechanical calculations are carried out on [Mn-amino acid]2+ complexes involving all 20 natural α-amino acids (AAs). Detailed investigation of [Mn-serine]2+, [Mn-cysteine]2+, [Mn-phenylalanine]2+, [Mn-tyrosine]2+, and [Mn-tryptophan]2+ indicates that with an electron-rich side chain, the most stable species involves interaction of Mn2+ with carbonyl oxygen, amino nitrogen, and an electron-rich section of the side chain of the AA in its canonical form. This is in sharp contrast with aliphatic side chains for which a salt bridge is formed. For aromatic AAs, complexation to manganese leads to partial oxidation as well as aromaticity reduction. Despite multisite binding, AAs do not generate strong enough ligand fields to switch the metal to a low- or even intermediate-spin ground state. The affinities of Mn2+ for all AAs are reported at the B3LYP and CCSD(T) levels of theory, thereby providing the first complete series of affinities for a divalent metal ion. The trends are compared with those of other cations for which affinities of all AAs have been previously obtained.

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