Characterization of a low redox potential laccase from the basidiomycete C30

A new exocellular laccase was purified from the basidiomycete C30. LAC2 is an acidic protein (pI = 3.2) preferentially produced upon a combined induction by copper and p -hydroxybenzoate. The spectroscopic signature (UV/visible and EPR) of this isoform is typical of multicopper oxidases, but its enzymatic and physico-chemical properties proved to be markedly different from those of LAC1, the constitutive laccase previously purified from the same organism. In particular, the LAC2 k (cat) values observed for the oxidation of the substrates syringaldazine (k (cat) = 65 600 min(-1) ), ABTS (2,2-azino-bis-[3-ethylthiazoline-6-sulfonate] (k (cat) = 41 000 min(-1) ) and guaiacol (k (cat) = 75 680 min(-1) ) are 10-40 times those obtained with LAC1 and the redox potential of its T1 copper is 0.17 V lower than that of LAC1 (E degrees = 0.73 V). This is the first report on a single organism producing simultaneously both a high and a low redox potential laccase. The cDNA, clac2 , was cloned and sequenced. It encodes a protein of 528 amino acids that shares 69% identity (79% similarity) with LAC1 and 81% identity (95% similarity) with Lcc3-2 from Polyporus ciliatus (AF176321-1), its nearest neighbor in database. Possible reasons for why this basidiomycete produces, in vivo , enzyme forms with such different behaviors are discussed.