Biological systems are very sensitive to the pressure of their environment. For example, high hydrostatic pressure can lead to the denaturation of proteins, which is incompatible with life. Despite this, deep-sea organisms thrive in a high pressure environment due to evolutionary adaptations that allow them to resist the denaturing effects of pressure. One example of such an adaptation is amino acid substitutions in their proteins, which have been observed in many species of deep-sea organisms.[1,2] However, the molecular mechanism by which these amino acid substitutions grant pressure-resistance is currently unknown. One explanation is that these substitutions result in an overall stabilization of the folded state over the pressure-denatured state, resulting in an increased ΔG of unfolding and a less favourable process.

In this work, the pressure-resisting effect of amino acid substitutions was studied on the enzyme lactate dehydrogenase from two related species: the Atlantic cod Gadus morhua, and a deep-sea fish, Coryphaenoides armatus. Twenty-one amino acid substitutions have been found in Coryphaenoides armatus lactate dehydrogenase compared with the Gadus morhua protein,[1] and these substitutions consist of a mixture of exposed, buried, nonpolar and polar residues. Alchemical free energy calculations were performed in order to calculate the effect each substitution had on the thermodynamics of unfolding. Here we present our findings, which indicate that thermodynamic stabilization of pressure-resistant proteins at high pressure occurs as a result of changes in interaction with the solvent water.

[1] A. A. Brindley et al, PLoS ONE, 3, e2042 (2008) [2] N. Ando et al, Annu. Rev. Biophys., 50, 343-372 (2021)