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 ° = 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. [ABSTRACT FROM AUTHOR]