Objectives: The purpose of our study was to obtain an acidic and cold-active tyrosinase, which potentially minimizes unwanted self-oxidation of tyrosinase-catalyzed catechols including 3,4-dihydroxyphenyl-alanine (DOPA) at elevated pH and high temperature.

Results: A putative psychrophilic tyrosinase (named as tyrosinase-CNK) was identified from the genome information of the marine archaeon Candidatus Nitrosopumilus koreensis in the Arctic Circle. This protein contains key tyrosinase domains such as copper-binding domains and an oxygen-binding motif, and phylogenetic analysis revealed that it was distinct from other known bacterial tyrosinase types. Functional tyrosinase-CNK was successfully produced by applying a co-expression strategy together with chaperone proteins in E. coli with the final yield of approximately 30 mg L-1 and a purity greater than 95% in native conditions in a 50-mL flask culture. The purified enzyme showed optimal activity at pH 6.0 and 20 ºC and still had 50% activity compared with the highest activity in ice water. Surprisingly, the enzyme exhibited an abnormally high monophenolase/diphenolase activity ratio.

Conclusions: The acidic and cold-adapted tyrosinase-CNK, as a new type of tyrosinase, could expand potential applications of tyrosinases including the production of catechols through minimizing unwanted self-oxidation and the modification of existing materials at low temperature.