Molecular characterization of a blue-copper laccase, TILA, of Aspergillus nidulans

Laccases are blue-copper enzymes, which oxidize phenolic substrates and thereby reduce molecular oxygen. They are widespread within fungi and are involved in lignin degradation or secondary metabolism such as pigment biosynthesis. Many fungi contain several laccases, not all of whose functions are known. In Aspergillus nidulans one, yA, is expressed during asexual development and converts a yellow precursor to the green pigment. We identified a second laccase gene, which encodes a 66.3-kDa protein 37.6% identical to laccase I of A. nidulans. The protein harbors an N-terminal secretion signal, and three characteristic copper-binding centers. The enzyme localizes at the growing hyphal tip. The gene was therefore named tilA (=tip laccase). Deletion or overexpression of the gene had no discernible phenotype under laboratory conditions.