An extracellular laccase with antiproliferative activity from the sanghuang mushroom Inonotus baumii

We described the purification and characterization of a novel extracellular laccase from the traditional Chinese medicinal mushroom Inonotus baumii with antiproliferative activity. The laccase (IBL) was purified from fermentation broth of I. baumii by employing initial filtration and centrifugation steps, followed by three ion-exchange chromatography steps comprising DEAE-cellulose, CM-cellulose, and Q-Sepharose, and a final gel-filtration step by fast protein liquid chromatography (FPLC) on Superdex 75. The purified enzyme was a monomeric protein with a molecular mass of 66 kDa calculated by FPLC and SDS-PAGE. It possessed an N-terminal amino acid sequence of AIGPVDEV (SPIN: C0HJB2), a temperature optimum of 20 °C, pH optima of 2.4 and 3.2 toward ABTS and guaiacol respectively, and Km values of 1.31 mM and 2.27 mM toward ABTS and guaiacol respectively at pH 2.4 and 30 °C. The ranking of its oxidative activity toward various aromatic substrates was ATBS > guaiacol > 4-methylcatechol > 4-hydroxyindole > catechol > hydroquinone > 2,6-dimethoxy-phenol (19.6%) > pyrogallol > ferulic acid > N, N-dimethyl-1, 4-phenylenediamine. Cu2+ can enhance the enzyme activity of 10.8–14.6 fold in the ion concentration range of 1.25–10 mM. IBL manifested antiproliferative activities toward HepG2 and L1210 cells with IC50 values of 2.4 μM and 3.2 μM, respectively, but is devoid of inhibitory activity toward HIV-1 reverse transcriptase.