Transesterification with CE15 glucuronoyl esterase from Cerrena unicolor reveals substrate preferences.

PURPOSE: Glucuronoyl esterases (GE, family CE15) catalyse the cleavage of ester linkages in lignin-carbohydrate complexes (LCCs), and this study demonstrate how transesterification reactions with a fungal GE from Cerrena unicolor (CuGE) can reveal the enzyme's preference for the alcohol-part of the ester-bond. METHODS: This alcohol-preference relates to where the ester-LCCs are located on the lignin molecule, and has consequences for how the enzymes potentially interact with lignin. It is unknown exactly what the enzymes prefer; either the α-benzyl or the γ-benzyl position. By providing the enzyme with a donor substrate (the methyl ester of either glucuronate or 4-O-methyl-glucuronate) and either one of two acceptor molecules (benzyl alcohol or 3-phenyl-1-propanol) we demonstrate that the enzyme can perform transesterification and it serves as a method for assessing the enzyme's alcohol preferences. CONCLUSION: CuGE preferentially forms the γ-ester from the methyl ester of 4-O-methyl-glucuronate and 3-phenyl-1-propanol and the enzyme's substrate preferences are primarily dictated by the presence of the 4-O-methylation on the glucuronoyl donor, and secondly on the type of alcohol.