Canadian Forest Service Publications
*Biochemical studies of the multicopper oxidase (small laccase) from Streptomyces coelicolor using bioactive phytochemicals and site-directed mutagenesis. 2013. Sherif, M.; Waung, D.; Korbeci, B.; Mavisakalyan, V.; Flick, R.; Brown,G.; Abou-Zaid, M.; Yakunin, A.F.; Master, E.R. Microbial Biotechnology 6(5):588-597.
Year: 2013
Issued by: Great Lakes Forestry Centre
Catalog ID: 35152
Language: English
Availability: PDF (request by e-mail)
Abstract
Multicopper oxidases can act on a broad spectrum of phenolic and non-phenolic compounds. These enzymes include laccases, which are widely distributed in plants and fungi, and were more recently identified in bacteria. Here, we present the results of biochemical and mutational studies of small laccase (SLAC), a multicopper oxidase from Streptomyces coelicolor (SCO6712). In addition to typical laccase substrates, SLAC was tested using phenolic compounds that exhibit antioxidant activity. SLAC showed oxidase activity against 12 of 23 substrates tested, including caffeic acid, ferulic acid, resveratrol, quercetin, morin, kaempferol and myricetin. The kinetic parameters of SLAC were determined for 2,2- azino-bis(3-ethylbenzthiazoline-6-sulphonic acid), 2,6-dimethoxyphenol, quercetin, morin and myricetin, and maximum reaction rates were observed with myricetin, where kcat and Km values at 60°C were 8.1 ( 0.8) s-1 and 0.9 ( 0.3) mM respectively. SLAC had a broad pH optimum for activity (between pH 4 and 8) and temperature optimum at 60–70°C. It demonstrated remarkable thermostability with a half-life of over 10 h at 80°C and over 7 h at 90°C. Site-directed mutagenesis revealed 17 amino acid residues important for SLAC activity including the 10 His residues involved in copper coordination. Most notably, the Y229A and Y230A mutant proteins showed over 10-fold increase in activity compared with the wildtype SLAC, which was correlated to higher copper incorporation, while kinetic analyses with S929A predicts localization of this residue near the metaposition of aromatic substrates.
Plain Language Summary
Laccases are copper-containing oxidase enzymes that are found in fungi and more recently have been identified in bacteria. They are of interest because their oxidative versatility lends them to multiple uses in industry. For example, they can be used as catalysts, or for the depolymerization of lignin. We studied small laccase, a multicopper oxidase from the bacteria Streptomyces coelicolor. We performed a variety of biochemical and mutational studies. We tested its oxidase activity against various phenolic compounds, including a number of substrates that exhibit antioxidant activity. We determined the temperature and pH for optimal reaction conditions. We investigated the possibility of using site-directed mutagenesis (a molecular biology method used to make specific changes to the genetic makeup) to improve its catalytic efficiency.