|Biely, Peter - SLOVAK ACADEMY OF SCIENCE|
Submitted to: American Chemical Society National Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 18, 2004
Publication Date: March 18, 2005
Citation: Biely, P., Cote, G.L. 2005. Microbial acetylxylan esterases: twenty years after their discovery [abstract]. American Chemical Society National Meeting, March 13-18, 2005, San Diego, California. Paper CELL185. Technical Abstract: Twenty years have passed since the first report of microbial esterases that deacetylate partially acetylated hardwood 4-O-methyl-D-glucuronoxylan. Since that time, numerous enzymes of similar activity have been purified from hemicellulolytic and cellulolytic systems of microorganisms. The discovery also led to identification of other types of esterases such as acetylgalactomannan esterase, acetylpectin esterase, and feruloyl esterase. The term carbohydrate esterase (CE) has been introduced for these enzymes together with their classification into families. The acetylxylan esterases (AcXE) were found to be the most diverse components of the plant cell wall degrading enzyme systems. They have been classified into 7 of 14 carbohydrate esterase families. Many of the enzymes are serine type esterases similar to lipases. Only a few CEs have been crystallized and had their 3D structure established. Some of the enzymes, such as the AcXE from Streptomyces lividans (CE family 4), do not seem to be serine type esterases. This enzyme shows unique behaviour on a variety of synthetic substrates, and under special conditions it exhibits chitin deacetylase activity. Its O-deacetylation mechanism is strongly dependent on the presence of the neighbouring OH-group. Recent studies of the positional specificity of AcXEs using 2-, 3-, and 4-O-acetyl 4-nitrophenyl beta-D-xylopyranosides have shown that the acetyl group at position 2 is the target of the enzymes. Deacetylation of position 3 in methyl beta-D-xylopyranosides seems to be due to binding of the substrates to enzymes in a reverse orientation. Additional interest in AcXEs concentrates on their synthetic potential, especially their ability to catalyze acetylation of carbohydrates and natural fibrils.