白腐真菌木质素降解酶的产生及其调控机制研究进展

Review on the production and regulation mechanism of ligninolytic enzymes of the white rot fungi

以黄孢原毛平革菌为主,介绍了近年来白腐真菌木质素降解酶系的生理生化特性、基因组成及其调控的研究进展,并且对木质素降解酶系的外源性调控及其酶活的失活机制进行了综述。然而,尽管对白腐真菌木质素降解酶的研究已有很大的进展,但木质素降解酶的分子调控机制仍尚未明了。

The present article aims at introducing the research progresses of the production and regulation mechanism of ligninolytic enzymes of white rot fungi. White rot fungi tend to degrade many persistent pollutants due to the contribution of the extracellular ligninolytic enzymes. The major components of the ligninolysis system of the white rot fungi include lignin peroxidases (LiPs), manganese-dependent peroxidases (MnPs), laccases and H_2O_2-generating enzymes. The stress of this paper has been put on the study of the biochemical and molecular properties of ligninolytic enzymes of white rot fungi, mainly of Phanerochaete chrysosporium, one of the most extensively studied white rot fungi. The gene structure, expression and regulation of ligninolytic enzymes, as well as its exogenous regulation and inactivation have been discussed. Phanerochaete chrysosporium mainly secrects Lips and MnPs which belong to the families of extracellular glycosylated heme proteins generated during idophase. To be exact, the LiPs constitute a large family of 15 isozymes encoded by a family of at least ten structurally related genes. A detailed physical map of the genomic organization of the lip genes has been constructed. The sequences of cDNA and genomic clones encoding the three MnP isozymes of Phanerochaete chrysosporium have been determined. The exogenous regulation and gene regulation experiments have indicated that the type and relative abundance of LiP isozymes secreted by Phanerochaete chrysosporium depend on the strains employed, culture conditions and the purification procedures. Ligninolysis enzymes and genes are differently regulated and respond to different environment. No apparent correlation has been found between the lip genomic structure and transcript levels. High oxygen concentration may lead to the increased production of reactive oxygen species (ROS) which are necessary to trigger LiPs expression. Therefore it is suggested that LiPs be synthesized as a stress protein in response to oxidant stress. MnPs are regulated at transcription level by Mn(II), heat shock and oxidant stress. Ligninolysis enzymes activity would decrease sharply after a six days of cultivation, which may result from the extracelluar protease, H_2O_2 and the decline of pH.