Discovery of a novel glucuronan lyase system in Trichoderma parareesei.

Glucuronan lyases (EC 4.2.2.14) catalyze depolymerization of linear β-(1, 4)-polyglucuronic acid (glucuronan). Only a few glucuronan lyases have been characterized until now, most of them originating from bacteria. Here we report the discovery, recombinant production, and functional characterization of the full complement of six glucuronan specific polysaccharide lyases in the necrotic mycoparasite Trichoderma parareesei. The enzymes belong to four different polysaccharide lyase families and have different reaction optima and glucuronan degradation profiles. Four of them showed endo-lytic action and two, TpPL8A and TpPL38A, displayed exo-lytic action. NMR revealed that the monomeric end-product from TpPL8A and TpPL38A underwent spontaneous rearrangements to tautomeric forms. Proteomic analysis of the secretomes from T. parareesei growing on pure glucuronan and lyophilized A. bisporus fruiting bodies, respectively, showed secretion of five of the glucuronan lyases and HPAEC-PAD analysis confirmed the presence of glucuronic acid in the A. bisporus fruiting bodies. By systematic genome annotation of more than 100 fungal genomes and subsequent phylogenetic analysis of the putative glucuronan lyases, we show that glucuronan lyases occur in several ecological and taxonomic groups in the fungal kingdom. Our findings suggest that a diverse repertoire of glucuronan lyases is a common trait among Hypocreales spp. with mycoparasitic and entomopathogenic lifestyles. IMPORTANCE This paper reports the discovery of a set of six complementary glucuronan lyase enzymes in the mycoparasite Tricoderma parareseei. Apart from the novelty of the discovery of these enzymes in T. parareesei, the key importance of the study is the finding that the majority of these lyases are induced when T. parareseei is inoculated on Basidiomycete cell walls that contain glucuronan. The study also reveals putative glucuronan lyase encoding genes in a wealth of other fungi that furthermore points at fungal cell wall glucuronan being a target C-source for many types of fungi. In a technical context, the findings may lead to controlled production of glucuronan oligomers for advanced pharmaceutical applications and pave the way for development of new fungal biocontrol agents.