|Biely, Peter - SLOVAK ACADEMY|
|Mastihubova, Maria - SLOVAK ACADEMY|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 31, 2002
Publication Date: N/A
Technical Abstract: Acetylxylan esterases (AcXEs) belong to recently discovered components of microbial hemicellulolytic systems. Their role is to remove acetyl groups esterifying xylopyranosyl residues of glucuronoxylan, the main hardwood hemicellulose. The substrate specificity of several representatives of AcXEs of CE families 1, 4, and 5 was investigated on partially and fully acetylated methyl glycopyranosides. To investigate the role of the free OH-group at positions 3 or 2 in the deacetylation mechanism of positions 2 and 3 and in the substrate binding by Streptomyces lividans AcXE, 2-deoxy-, 2-deoxy-2-fluoro-, 3-deoxy-, and 3-deoxy-3-fluoro analogues of acetylated Me-BETA-Xylp were synthesized. The replacement of the OH-groups by H or by F reduced the rate of deacetylation of position 2 or 3 to the rate of fully acetylated Me-beta-Xylp. These results pointed to a crucial role of the vicinal OH-groups in the deacetylation mechanism or in the enzyme-substrate interaction. These observations confirmed the structural requirement of the enzyme for the spatial arrangement of the hydroxyl and acetyl groups on carbon atoms 2 and 3 as that found in xylo- and glucopyranosides. We can say that the regioselectivity of deacetylation of carbohydrates by AcXEs is complementary to that exhibited by non-hemicellulolytic esterases and lipases, which attack mainly acetyl groups at position 4 or at primary hydroxyl groups.