Carbohydrate esterases of family 2 are 6‐O‐deacetylases

Abstract

a b s t r a c tThree acetyl esterases (AcEs) from the saprophytic bacteria Cellvibrio japonicus and Clostridium thermocellum, members of the carbohydrate esterase (CE) family 2, were tested for their activity against a series of model substrates including partially acetylated gluco-, manno-and xylopyranosides. All three enzymes showed a strong preference for deacetylation of the 6-position in aldohexoses. This regioselectivity is different from that of typical acetylxylan esterases (AcXEs). In aqueous medium saturated with vinyl acetate, the CE-2 enzymes catalyzed transacetylation to the same position, i.e., to the primary hydroxyl group of mono-and disaccharides. Xylose and xylooligosaccharides did not serve as acetyl group acceptors, therefore the CE-2 enzymes appear to be 6-Odeacetylases.

Understanding the structural and functional properties of carbohydrate esterases with a special focus on hemicellulose deacetylating acetyl xylan esterases

“…The CE class-2 AcXEs are active on hexopyranosyl residues of the oligo- and polysaccharides with lower activity against acetylxylan and xylanoside residues. These enzymes are known for its transesterification reactions of hexose and hexosyl residues specifically on position 6, respectively (Dalrymple et al 1997; Montanier et al 2009b; Topakas et al 2010). In contrast with class-1 and 2 enzymes, CE class-3 AcXEs exhibit substrate specificity towards a wide range of acetylated carbohydrate residues.…”

Phylogeny, classification and metagenomic bioprospecting of microbial acetyl xylan esterases

“…These activities may facilitate the action of other CAZymes associated with plant cell wall degradation. Interestingly, CEs (CE2 and CE16) have also been implicated in transesterification reactions [23,24].…”

“…Certain AcXEs were reported to bind to other plant cell wall polymers such as cellulose and arabinoxylan while independently deacetylating xylan, thus increasing accessibility of other lignocellulases to decaying plant material [29,40]. Other substrates on which AcXEs have been reported to be active include acetylated monosaccharides [23,41], triacetin [30], α-napthyl acetate [42], tri-O-acetyl-Dgalactal [43], p-nitrophenyl acetate [1], short chain alkyl acetates and 4-methylumbelliferyl acetate [44]. Certain AcXEs have also been shown to have a higher rate of deacetylation when in synergistic action with xylanases [43,45].…”

“…CE2 AcXEs, which were first described by Dalrymple, Cybinski [63] in the fungus Neocallimastix patriciarum, are active on acetylated birchwood xylan and α-naphthyl acetate. The CE2 AcXEs from Cellvibrio japonicus and Clostridium thermocellum have been best characterised and are reported to be generally active on aryl esters and selectively active on acetylated xylan, showing higher activities on acetylated konjac glucomannan than on acetylated birchwood xylan and diacetylated xylopyranosides [23,64]. The CE2 AcXEs are serine-type esterases with a Ser-His catalytic diad and an α-β hydrolase protein fold [64].…”

“…The CE2 AcXEs are serine-type esterases with a Ser-His catalytic diad and an α-β hydrolase protein fold [64]. They possess the GDS(L) conserved motif and exhibit deacetylase specificity for the C6 position of acetylated gluco-and mannopyranosyl residues of hemicellulose substrates, and for the C4 and C3 positions on monoacetylated xylopyranosyl residues [23]. 6-O-deacetylase activity has not been reported for any member of other CE families.…”