Solvation of halophilic proteins

My collaborators at the Institut of Biologie Structurale in Grenoble (FR), D. Madern and E. Girard along with the PhD student R. Tallon, just published an interesting work in Frontier (Microbiology/Extreme Microbiology), see the manuscript here. They report a detailed comparison between the structures of two homologous proteins: the halophilic tetrameric malate from the bacterium Salinibacter ruber (Sr) and the non-halophilic malate from the bacterium Chloroflexus aurantiacus (Ca). The core of the discussion concerns the role of hydration on extreme adaptation and relates to the different surface compositions of the two proteins, and the potential different coupling with the solvent layer.

First, the structures are resolved at very high-resolution. Second, the protein from Ca is resolved with a huge number of hydration molecules surrounding the protein surface and hydrating some internal locations. The presence of this well defined hydration layer around the non-halophilic protein allows to individuate precise closed structures of water, à voir pentagons, surrounding some hydrophobic patches of the surface. On the contrary the x-ray structure of the halophilic protein from the Sr bacterium lacks a well defined hydration layer and no clusters of water were visualized. Therefore the authors concluded that the chemical composition of the surface of the halophilic protein, enriched in negatively charged amino-acids, makes unfavorable for water to create extended closed networks of hydrogen bonds.

Then, and this is more speculative, the authors discuss how the enrichment in  negatively charged amino-acids could play a role for i) solubility in high-salt concentration and ii) salt-in effects observed in halophilic proteins.
Stay tuned on the blog because we are currently investigating how the life of a protein at ambient condition influences the stability of the water hydrogen bonds networks at the protein surface. For the moments, some hints from our past studies: i) role of protein surface on dynamics and structure of interfacial water (see here), ii) water networks at protein surface and protein stability (see here), iii) a molecular vision of protein hydration (see here), iv) proteins compositions and water dynamics (see here).

Halophile bacteria in Lake Natron, Tanzania