Expression and characterization of a recombinant psychrophilic ?-carbonic anhydrase (NcoCA) identified in the genome of the Antarctic cyanobacteria belonging to the genus Nostoc

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyze the CO<inf>2</inf> hydration/dehydration reversible reaction: CO<inf>2</inf> + H<inf>2</inf>O ? (Formula presented.) + H⁺. Living organisms encode for at least six distinct genetic families of such catalyst, the ?-, ?-, ?-, ?-, ?- and ?-CAs. The main function of the CAs is to quickly process the CO<inf>2</inf> derived by metabolic processes in order to regulate acid-base homeostasis, connected to the production of protons (H⁺) and bicarbonate. Few data are available in the literature on Antarctic CAs and most of the scientific information regards CAs isolated from mammals or prokaryotes (as well as other mesophilic sources). It is of great interest to study the biochemical behavior of such catalysts identified in organism living in the Antarctic sea where temperatures average -1.9 °C all year round. The enzymes isolated from Antarctic organisms represent a useful tool to study the relations among structure, stability and function of proteins in organisms adapted to living at constantly low temperatures. In the present paper, we report in detail the cloning, purification, and physico-chemical properties of NcoCA, a ?-CA isolated from the Antarctic cyanobacterium Nostoc commune. This enzyme showed a higher catalytic efficiency at lower temperatures compared to mesophilic counterparts belonging to ?-, ?-, ?-classes, as well as a limited stability at moderate temperatures.