Characterization of an aminotransferase TlBCAT from Trichoderma longibrachiatum UN32 involved in dendrobine-type total alkaloids biosynthesis.

Trichoderma longibrachiatum UN32 is an industrially important fungus capable of producing Dendrobine-Type Total alkaloids (DTTAs). Several reports have pointed out that branched-chain amino acid aminotransferases (BCATs) participate in backbone modification or promote the production of secondary metabolites. We previously proposed that cobalt chloride increased DTTAs production in T. longibrachiatum UN32, which was associated with enhanced expression of the gene BCAT, TlBCAT (Genbank accession No. PP465542). Following cloning and characterization, the cDNA of TlBCAT was found to consists of 1191 bp, encoding a protein of 397 amino acid residues. The molecular mass of TlBCAT was about 42 kDa through SDS-PAGE analysis. The predicted pI value was 5.54. Recombinant TlBCAT can catalyze L-leu with a catalytic efficiency of 15.91 mM^- 1S^- 1. In the binding pocket, residues interacting with PLP, including Tyr68, Arg93, Tyr136, and Lys194, are highly conserved. TlBCAT exhibits a broad spectrum of substrate specificity, typical for catalyzing the transamination reaction of various branched-chain and hydrophobic amino acids, with α-ketoglutarate as the amino acceptor. Exogenous branched-chain amino acids (BCAAs) positively affect Trichoderma growth and DTTAs production. These findings offer insights into the physiological significance of BCAAs and present a novel approach for enhancing DTTAs production in Trichoderma mycelium cultures.