Ion-induced alterations of the local hydration environment elucidate Hofmeister effect in a simple classical model of Trp-cage miniprotein

Protein stability is known to be influenced by the presence of Hofmeister active ions in the solution. In addition to direct ion-protein interactions, this influence manifests through the local alterations of the interfacial water structure induced by the anions and cations present in this region. In our earlier works it was pointed out that the effects of Hofmeister active salts on the stability of Trp-cage miniprotein can be modeled qualitatively using non-polarizable force fields. These simulations reproduced the structure-stabilization and structure-destabilization effects of selected kosmotropic and chaotropic salts, respectively. In the present study we use the same model system to elucidate atomic processes behind the chaotropic destabilization and kosmotropic stabilization of the miniprotein. We focus on changes of the local hydration environment of the miniprotein upon addition of NaClO4 and NaF salts to the solution. The process is separated into two parts. In the first, ‘promotion’ phase, the protein structure is fixed, and the local hydration properties induced by the simultaneous presence of protein and ions are investigated, with a special focus on the interaction of Hofmeister active anions with the charged and polar sites. In the second, ‘rearrangement’ phase we follow changes of the hydration of ions and the protein, accompanying the conformational relaxation of the protein. We identify significant factors of an enthalpic and entropic nature behind the ion-induced free energy changes of the protein-water system, and also propose a possible atomic mechanism consistent with the Collins’s rule, for the chaotropic destabilization and kosmotropic stabilization of protein conformation

The interfacial tension concept, as revealed by fluctuations

Abstract A simple, didactic model that could have conclusively interpreted the complexity of specific salt (Hofmeister-) effects on protein solubility and function, using a single physical quantity as a central parameter, has long been missing. Via surveying a row of recent papers we show in this review that a phenomenological formalism based on the salt-induced change of protein–water interfacial tension (∆γ) is able to account for a wide range of Hofmeister effects, including also such “exceptions”, where inverse or “V-shaped” Hofmeister series occurs. A close relationship between protein–water interfacial tension and conformational fluctuations is pinpointed on theoretical grounds, then it is shown how one can use a complex experimental arsenal to demonstrate conformational fluctuations on two prototypical proteins, the membrane protein bacteriorhodopsin and the cytoplasmic protein myoglobin. Finally, via the results of recent and new molecular dynamics simulations on a model peptide, the tryptophan-cage miniprotein, independent evidences are given in favor of the interfacial tension concept, at the same time demonstrating the predictive power of the theory. It is shown that salt-induced fluctuation changes of surface-exposed amino acid groups can be used as a sensitive measure for mapping the local features of Hofmeister effects on protein conformations. General implications of the interfacial tension concept are also discussed

Structural characterization of the short peptaibols trichobrachins by molecular-dynamics methods

A structural characterization was carried out by molecular-dynamics methods for eight trichobrachin peptides, to identify the conformational features of these short peptaibols. For all peptides, the backbone and side-chain conformations were investigated, different secondary structures, such as type-I and -III bturns as well as b-bend ribbon spirals, were determined in certain tetrapeptide units of the molecules, and the preferred rotamers of the side chains of amino acids were identified. Furthermore, the end-to-end and residue-residue distances were examined, as well as the fluctuations of backbone atoms were studied. Based on these results, the peptides were compared to one another. Our theoretical study indicated that trichobrachins could be characterized by typical structural properties, and both conformational similarities and dissimilarities were observed between these peptaibols. In summary, this structural investigation supplied a characterization of the various conformational features of eight trichobrachin peptides