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

Abstract

Extracellular liquid of the edible fungus Lepista irina was found to effectively degrade beta,beta-carotene. beta-Ionone, beta-cyclocitral, dihydroactinidiolide, and 2-hydroxy-2,6,6-trimethylcyclohexanone were formed as volatile breakdown products of beta,beta-carotene with myceliumfree culture supernatants, whereas beta-apo 10'-carotenal was identified as nonvolatile 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 34degreesC and pH values between 3.5 and 4. Degenerate oligonucleotides were derived from Nterminal and internal amino acid sequences. By means of PCRbased cDNAlibrary 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 Nterminal 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.