Dynamic structure mediates halophilic adaptation of a DNA polymerase from the deep-sea brines of the Red Sea

The deep-sea brines of the Red Sea are remote and unexplored environments characterized by high temperatures, anoxicwater, and elevated concentrations of salt and heavymetals. This environment provides a rare system to study the interplay between halophilic and thermophilic adaptation in biologicmacromolecules. The present article reports the first DNA polymerase with halophilic and thermophilic features. Biochemical and structural analysis by Raman and circular dichroism spectroscopy showed that the charge distribution on the protein's surface mediates the structural balance between stability for thermal adaptation and flexibility for counteracting the salt-induced rigid and nonfunctional hydrophobic packing. Salt bridge interactions via increased negative and positive charges contribute to structural stability. Salt tolerance, conversely, is mediated by a dynamic structure that becomes more fixed and functionalwith increasing salt concentration.Wepropose that repulsive forcesamongexcessnegative charges, inaddition to ahighpercentage of negatively charged random coils,mediate this structuraldynamism.Thisknowledge enabledus to engineer a halophilic version of Thermococcus kodakarensisDNApolymerase.