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PhD. Topics

Institute of Chemistry

Auxiliary xylanolytic enzymes
PhD. program
Name of the supervisor
Mgr. Vladimír Puchart, PhD.
Receiving school
Faculty of Natural Sciences, Commenius University Bratislava
Xylan is a principal hemicellulose of hardwoods. It is also abundant in softwoods. Moreover, it is one of the storage polysaccharides found in cereal seeds. It is a pentosan, its backbone is composed of  1,4 linked xylopyranosyl units that are to a various extent decorated by different side chains. The influence of these branches on endoxylanases, the main enzymes degrading the polysaccharide, is well understood. However, there is a paucity of knowledge on the influence of the branches on the action of so-called auxiliary xylanolytic enzymes. In particular, the influence of other substituents in the vicinity of the linkage to be cleaved is poorly recognized. It will be the topic of the Ph. D. thesis. More specifically, the effect of various combinations of acetic acid, (4 O methyl-) D glucuronic acid and  L arabinofuranose linked to the same or penultimate xylosyl residue will be studied. As the substrates, commercially available, home-made as well as chemically synthesized oligosaccharides will be used to differentiate various types of acetylxylan esterases,  glucuronidases and  xylosidases. On the basis of amino acid sequences, all these enzymes are grouped to various carbohydrate esterase and glycoside hydrolase families but this classification is not related to the recognition or tolerance of the substrates that are decorated in a more complex manner. These complex substances are thought to be natural substrates for the above mentioned and so far underestimated enzymes that are, however, also important for economically feasible utilization of plant biomass.
Aims: 1. To unravel a reason for structural diversity of many auxiliary xylanolytic enzymes – beta-xylosidases, alpha-L-arabinofuranosidases, alpha-glucuronidases and acetylxylan esterases; 2. To study substrate specificity of various auxiliary xylanolytic enzymes; 3. To establish their structure-substrate specificity-biological function relationship