Lignin is the most abundant aromatic polymer in nature and a promising renewable source for the provision of aromatic platform chemicals and biofuels. beta-Etherases are enzymes with a promising potential for application in lignin depolymerization due to their selectivity in the cleavage of beta-O-4 aryl ether bonds. However, only a very limited number of these enzymes have been described and characterized so far. Using peptide pattern recognition (PPR) as well as phylogenetic analyses, 96 putatively novel beta-etherases have been identified, some even originating from bacteria outside the order Sphingomonadales. A set of 13 diverse enzymes was selected for biochemical characterization, and beta-etherase activity was confirmed for all of them. Some enzymes displayed up to 3-fold higher activity than previously known beta-etherases. Moreover, conserved sequence motifs specific for either LigE- or LigF-type enzymes were deduced from multiple-sequence alignments and the PPR-derived peptides. In combination with structural information available for the beta-etherases LigE and LigF, insight into the potential structural and/or functional role of conserved residues within these sequence motifs is provided. Phylogenetic analyses further suggest the presence of additional bacterial enzymes with potential beta-etherase activity outside the classical LigE- and LigF-type enzymes as well as the recently described heterodimeric beta-etherases.
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