An On-Demand Metalloprotease from Psychro-Tolerant Exiguobacterium undae Su-1, the Activity and Stability of Which Are Controlled by the Ca2+ Concentration

We reported an on-demand type of metalloprotease from Exiguobacterium undae Su-1. Although this species of bacterium is known to inhabit the permafrost, there are no reports on either strong proteases or peptidases. We found that Su-1 protease is superior to commercially available proteases in proteolytic activity in a lower to normal range of temperature (10–50 °C) as well as in rapid inactivation heat-dependently on the Ca²⁺ concentration. These characteristics meet well with the demands from food processing and manufacturing. Biochemical investigations of the purified enzyme and protein structural analysis after gene cloning confirmed that Su-1 protease conserved high identity in its primary sequence with thermophilic proteases of the M4 family. On the other hand, its flexibility was enhanced when one Ca²⁺ binding site was lost and by replacement for proline and isoleucine residues.