Adaptation of Folding and Function of a Nuclease from the Cold Deep Sea.

The majority of the Earth's microbial biomass is found in high pressure environments, raising the question of how protein sequences adapt to such environments. Pressure adaptation is more complex, and less well-understood, than adaptation to extreme temperatures since in high pressure environments, these two thermodynamic parameters are often coupled, as in the cold deep-sea or at hydrothermal vents. To begin to address this question, we investigated the functional and folding properties of an exonuclease, Cnase, from the first Gram positive piezophile to be sequenced, Carnobacterium sp. AT7, isolated at 2500 m depth and at ∼2 °C in the Aleutian trench in the North Pacific. We find that Cnase is a bonafide exonuclease, despite its high negative charge. We also find that Cnase largely conserves the structure and folding mechanism of its mesophilic and well-studied homolog, staphylococcal nuclease, Snase, despite significant differences in their sequences.