Production of 3,4-dihydroxy-L-phenylalanine using novel tyrosinases from Bacillus megaterium

Tyrosinases, type-3 copper proteins responsible for melanin formation in various organisms, have considerable potential to produce bioactive catechol derivatives such as 3,4-dihydroxy-L-phenylalanine (L-DOPA). They catalyze the ortho-hydroxylation of L-tyrosine to L-DOPA via monophenolase activity and the subsequent oxidation of L-DOPA to dopaquinone through diphenolase activity, which then spontaneously converts to melanin. In this study, six novel Bacillus megaterium strains, GJ802, GJ803, DY801, DY802, DY804, and DY805, were isolated from rice straw in South Korea. The tyrosinases of the novel strains were cloned, purified, and characterized. They exhibited catalytic activity over a broad pH range and showed high thermal stability. In addition, a tyrosinase of the B. megaterium DY805 strain (DY805), having the highest monophenolase activity among the tyrosinases, was used to produce L-DOPA as a biocatalyst. DY805 produced 8.77 mg/L L-DOPA from 200 µM L-tyrosine (36.2 mg/L), with a yield of 23.3%. After the optimization of several parameters for L-DOPA production, DY805 could produce up to 264 mg/L L-DOPA (30-fold increase), with a yield of 97.2% from 1500 µM L-tyrosine (272 mg/L). Taken together, these novel tyrosinases could be considered useful biocatalysts in L-DOPA production and other biotechnology fields.