Tat-dependent heterologous secretion of recombinant tyrosinase in Pseudomonas fluorescens is aided by translationally fused caddie protein

Tyrosinase is a monooxygenase that catalyzes both hydroxylation of p-hydroxyphenyl moieties to o-catechols and oxidation of o-catechols to o-quinones. Apart from its critical functionality in melanogenesis and the synthesis of various neurotransmitters, the enzyme is also used in a variety of biotechnological applications, most notably mediating covalent cross-linking between polymers containing p-hydroxyphenyl groups, forming a hydrogel. Tyrosinases from genus Streptomyces are usually secreted as a complex with its caddie protein. In this study, we report an increased secretion efficiency observed when S. antibioticus tyrosinase gene melC2 were introduced to Pseudomonas fluorescens along with its caddie protein gene melC1, which has the DNA sequence for the Tat (twin-arginine translocation) signal. IMPORTANCE We observed that the S. antibioticus extracellular tyrosinase secretion was even higher in its non-natural translationally conjugated fusion protein form, compared to the natural complex of separated two polypeptides. The results of this study demonstrate that tyrosinase-expressing P. fluorescens can be a stable source of bacterial tyrosinase through exploiting the secretory machinery of P. fluorescens.