Structural and Kinetic Insights Into the Molecular Basis of Salt Tolerance of the Short-Chain Glucose-6-Phosphate Dehydrogenase From

Halophilic enzymes need high salt concentrations for activity and stability and are considered a promising source for biotechnological applications. The model study for haloadaptation has been proteins from the class of Archaea, where common structural characteristics have been found. However, the effect of salt on enzyme function and conformational dynamics has been much less explored. Here we report the structural and kinetic characteristics of glucose-6-phosphate dehydrogenase from (G6PDH) belonging to the short-chain dehydrogenases/reductases (SDR) superfamily. The enzyme was expressed in and successfully solubilized and refolded from inclusion bodies. The enzyme is active in the presence of several salts, though the maximum activity is achieved in the presence of KCl, mainly by an increment in the value, that correlates with a diminution of its flexibility according to molecular dynamics simulations. The high for glucose-6-phosphate and its promiscuous activity for glucose restrict the use of G6PDH as an auxiliary enzyme for the determination of halophilic glucokinase activity. Phylogenetic analysis indicates that SDR-G6PDH enzymes are exclusively present in , with G6PDH being the only enzyme characterized. Homology modeling and molecular dynamics simulations of G6PDH identified a conserved NLTXH motif involved in glucose-6-phosphate interaction at high salt concentrations, whose residues could be crucial for substrate specificity. Structural differences in its conformational dynamics, potentially related to the haloadaptation strategy, were also determined.