Biochemical characterization of a psychrophilic and halotolerant a-carbonic anhydrase from a deep-sea bacterium, Photobacterium profundum

Prokaryotic a-carbonic anhydrases (a-CA) are metalloenzymes that catalyze the reversible hydration of CO2 to bicarbonate and proton. We had reported the first crystal structure of a pyschrohalophilic a-CA from a deep-sea bacterium, Photobacterium profundum SS9. In this manuscript, we report the first biochemical characterization of P. profundum a-CA (PprCA) which revealed several catalytic properties that are atypical for this class of CA's. Purified PprCA exhibited maximal catalytic activity at psychrophilic temperatures with substantial decrease in activity at mesophilic and thermophilic range. Similar to other a-CA's, Ppr9A showed peak activity at alkaline pH (pH 11), although, PprCA retained 88% of its activity even at acidic pH (pH 5). Exposing PprCA to varying concentrations of oxidizing and reducing agents revealed that N-terminal cysteine residues in PprCA may play a role in the structural stability of the enzyme. Although inefficient in CO2 hydration activity under mesophilic and thermophilic temperatures, PprCA exhibited salt-dependent thermotolerance and catalytic activity under extreme halophilic conditions. Similar to other well-characterized a-CA's, PprCA is also inhibited by monovalent anions even at low concentrations. Finally, we demonstrate that PprCA accelerates CO2 biomineralization to calcium carbonate under alkaline conditions.

Automated summary

This manuscript reports the crystal structure and biochemical characterization of a-CA from Photobacterium profundum SS9. The enzyme showed unusual catalytic properties, including maximal activity at low temperatures, retention of activity at acidic pH, and salt-dependent activity under extreme halophilic conditions.