An unusual feruloyl esterase belonging to family VIII esterases and displaying a broad substrate range

A thermophilic compost metagenomic library constructed in Escherichia coli was functionally screenedfor novel esterases. Of the 110,592 fosmid clones screened, 25 clones demonstrated degradative activ-ity on glyceryl tributyrate (a hit rate of 1:4,423). Four clones displayed ferulic acid esterase activityand were sequenced using 454 Titanium sequencing technology. EstG34, a 410 amino acid protein, wasidentified as having high sequence identity with a number of bacterial -lactamases. EstG34 has theS-X-X-K motif which is conserved in class C -lactamases and family VIII carboxylesterases. Purifiedrecombinant EstG34 had a molecular mass of 42 kDa and displayed hydrolytic activity towards a vari-ety of p-nitrophenyl esters, hydroxycinnamic acid esters and -naphthol acetate. EstG34 represents thefirst family VIII carboxylesterase and -lactamase fold enzyme, able to hydrolyse ferulate and a numberof other hydroxycinnamic acid esters. In addition, EstG34 is the first reported FAE to not adopt the / hydrolase conformation. The sequence similarity and wide substrate utilization capability of this esterasecomplicates its placement within current classification systems, but also draws attention to the enzyme’spotential versatility.The National Research Foundation (NRF) and the Technology Innovation Agency (TIA), South Africa(Project number PB99/08).http://www.elsevier.com/locate/molcatb2016-08-31hb201