Molecular and biochemical characterization of a distinct tyrosinase involved in melanin production from Aeromonas media

Abstract

A new tyrosinase was isolated from Aeromonas media strain WS and purified to homogeneity. The purified tyrosinase, termed TyrA, had a molecular mass of 58 kDa and an isoelectric point of 4.90. It exhibited optimal monophenol and diphenol oxidase activities under basic conditions (pH>8.0). TyrA had a relatively higher affinity to diphenol substrate L-dihydroxyphenylalanine (L-dopa) than many other tyrosinases. EDTA or glutathione notably inhibited the enzymatic activities of TyrA, whereas Triton X-100 and SDS activated them. The full-length TyrA gene was cloned, and it encodes a 518 amino acid protein with little similarities to other reported tyrosinases. However, the purified recombinant TyrA expressed in Escherichia coli demonstrated tyrosinase activity. These results suggest that TyrA is the first reported distinct tyrosinase involved in melanin production in the genus Aeromonas.

Identification of YfiH and the Catalase CatA As Polyphenol Oxidases of Aeromonas media and CatA as a Regulator of Pigmentation by Its Peroxyl Radical Scavenging Capacity

“…Although we identified a tyrosinase, TyrA, from A. media strain WS (Wan et al, 2009), it does not seem to be important in melanin formation in this strain (Chai et al, 2012). Also, laccase has been reported in A. hydrophila WL-11 (Wu et al, 2010), but no homolog of this enzyme was present in the genomic sequences of A. media strain WS, A. salmonicida A449, A. caviae , or A. veronii B565 (Reith et al, 2008; Beatson et al, 2011; Li et al, 2011).…”

“…The PPOs are usually tyrosinases, but are occasionally laccase (Fairhead and Thöny-Meyer, 2012). We previously identified the PPO TyrA by native-PAGE at pH 9.0 from A. media strain WS (Wan et al, 2009). However, in this study, we noted that deletion of tyrA in the WS Δ hppD strain did not affect pigment production by the mutant when it was cultured in LB media supplemented with 2 mg/mL tyrosine.…”

The Family Aeromonadaceae

“…The pigment produced by A. media strain WS, isolated from lake water and identified by phenotypic characterization and 16S rDNA sequencing, was shown to be melanin (Wan et al 2009). Triggered by the photoprotective properties of this compound, the genome sequence of strain WS was determined (Chai et al 2012).…”

“…Most of these are transposases and hypothetical proteins with unknown functions, which may indicate its potential for gene exchange. Conversion of tyrosine by bacterial tyrosinase is thought to initiate one of the major pathways for melanin production (Wan et al 2009), but no predicted proteins for tyrosinase were found in the genome of strain WS. However, multiple other genes potentially involved in melanin formation, such as genes encoding phenylalanine 4-monooxygenase and pterin-4-alpha-carbinolamine dehydratase were identified.…”

Living in an Extremely Polluted Environment: Clues from the Genome of Melanin-Producing Aeromonas salmonicida subsp. pectinolytica 34mel T

“…A study performed with A. media revealed an enzyme (GenBank accession number ACD40043) that oxidizes L-DOPA and has little similarity to previously reported tyrosinases, and it was proposed that this enzyme is an atypical tyrosinase involved in melanin biosynthesis (50). The gene that codes for this protein is present in 34mel T (K931_01824) and in both melanogenic and nonmelanogenic Aeromonas strains.…”