Identification and characterization of a novel cold-tolerant extracellular protease from Planococcus sp. CGMCC 8088

A psychrophilic extracellular protease was isolated from the marine bacterium Planococcus sp. M7 found in the deep-sea mud of the Southern Indian Ocean. The mature protease is about 43 kDa and contains 389 amino acids. Sequence alignment revealed that the protease whose catalytic triad was comprised of Ser224, Lys249, and Gln253 contains a catalytic module belonging to the serralysin-type protease family 41, and displays 46.55% identity with the experimentally verified serine protease from Bacillus subtilis str. 168. The enzyme displayed an alkaline mesophilic preference with an optimum pH of 10.0 and an optimum temperature of 35 °C. The enzyme retained its activity from 5 to 35 °C and was resistant to repeated freezing and thawing, but was completely inactivated at 55 °C. Calcium ions had a protective effect against thermal denaturation. More than 60% of the maximum activity was retained at pH values in the range of 5.0-11.0. Almost no activity loss was detected after 1 h of incubation at pH 8.0-10.0 and 20 °C, or with 1.0% SDS. Most important, this protease also showed good stability and compatibility with the standard enzyme-free detergent, which indicates its special interest for applications in detergent industry.