Determination of <i>in cellulo</i> proteome molecular dynamics in different halophilic Archaea

While biophysical studies have unravelled properties of specific proteins <i>in vitro</i>, characterizing globally their native state within the cell remains a challenge. In particular, protein adaptation to harsh intracellular physical and chemical conditions is poorly understood. Extremophiles, which thrive in severe environments, are good models for the study of such adaptation. Five haloarchaeal species, isolated from hypersaline environments, were used to assess correlations between intracellular salt concentrations and molecular dynamics properties. <i>In cellulo</i> protein stability was measured using nano differential scanning fluorimetry, and neutron spectrometry was used to determine molecular dynamics resilience and global flexibility. It was found that high intracellular accumulation of Mg²⁺ and low intracellular accumulation of K⁺ were correlated with higher stability and resilience. Sequence traits associated with mean proteome halophilicity, such as decreased hydrophobicity and increased acidity, weighted by the relative abundance of each protein, were also correlated with stability and resilience. <i>Haloferax mediterranei</i>, however, was found to be an exception as its proteome showed the highest <i>in cellulo</i> molecular stability and resilience associated with fewest sequence traits related to halophilicity, highlighting the significance of the intracellular salt environment in determining proteome biophysical properties.