A peroxidase from Lepista irina cleaves beta,beta-carotene to flavor compounds

Extracellular liquid of the edible fungus Lepista irina was found to effectively degrade beta,beta-carotene, beta-lonone, beta-cyclocitral, dihydroactinidiolide, and 2-hydroxy-2,6,6-trimethylcyclohexanone were formed as volatile breakdown products of beta,beta-carotene with mycelium-free culture supernatants, whereas beta-apo-10'-carotenal was identified as non-volatile degradation product. The key enzyme catalyzing the oxidative cleavage of beta,beta-carotene was purified with an overall yield of 63% and a purification factor of 43. Biochemical characterization showed a molecular mass of 50.5 kDa and an isoelectric point of 3.75. Fastest beta,beta-carotene degradation occurred at 34 degrees C and pH values between 3.5 and 4. Degenerate oligonucleotides were derived from N-terminal and internal amino acid sequences. By means of PCR-based cDNA-library screening a 1284 bp cDNA was identified which showed great overall similarity to Pleurotus eryngii polyvalent peroxidases. The obtained sequence contains an open reading frame of 1083 nucleotides, encoding a polypeptide of 361 amino acids. A 30 amino acid signal peptide was identified upstream of the N-terminal sequence of the mature enzyme. The L. irina versatile peroxidase represents the first microbial enzyme capable of carotenoid degradation that has been characterized on a molecular level, proving the participation of extracellular enzymes of white rot fungi in biotic carotenoid degradation processes.