Decomposing Hofmeister effects on amino acid residues with symmetry adapted perturbation theory

Hofmeister effects, and more generally specific ion effects, are observed broadly in biological systems. However, there are many cases where the Hofmeister series might not be followed in complex biological systems, such as ion channels which can be highly specific to a particular ion. An understanding of how ions from the Hofmeister series interact with the proteinogenic amino acids will assist elucidation of why some binding interactions may be favoured over others. Using symmetry adapted perturbation theory (SAPT2 + 3), the interaction energies between a selection of anions and each amino acid have been investigated. The interaction strengths become more favourable in accordance with the Hofmeister series, and also with increasing polarity of the amino acids (with the exception of the negatively charged amino acid side chains). Furthermore, the interactions are generally most favourable when they simultaneously involve the side chain and both protic moieties of the backbone. The total interaction energy in these anion-amino acid complexes is also primarily determined by its electrostatic component, in a manner proportional to the thorn ('sho') value of the anion.

Automated summary

Hofmeister effects and specific ion effects are common in biological systems, but they may not always follow the Hofmeister series in complex biological systems like ion channels. Studying the interaction energies between anions and amino acids can help explain why certain binding interactions are favored. The strength of interactions follows the Hofmeister series and increases with the polarity of amino acids, except for negatively charged amino acid side chains. Interactions involving both the side chain and protic moieties of the backbone are generally most favorable, and the total interaction energy is primarily determined by the electrostatic component and the thorn ('sho') value of the anion.