|Cote, Gregory - Greg|
Submitted to: European Journal of Biochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/2003
Publication Date: 9/1/2003
Citation: BIELY, P., MASTIHUBOVA, M., GREENE, R.V., COTE, G.L. MODE OF ACTION OF ACETYLXYLAN ESTERASE FROM STREPTOMYCES LIVIDANS: A STUDY WITH DEOXY AND DEOXY-FLUORO ANALOGUES OF ACETYLATED METHYL BETA-D-XYLOPYRANOSIDE. EUROPEAN JOURNAL OF BIOCHEMISTRY. 2003. V. 1622. P. 82-88. Interpretive Summary: Biological catalysts from microbes help break down plant matter in the soil. The action of a biological catalyst from a soil microbe was studied on synthetic compounds that mimic the natural plant matter. From these experiments, we were able to learn more about how the catalyst works. This knowledge not only helps us understand how microbes break down organic matter in the soil, but also enable us to use these biological catalysts in so-called "green technology," such as producing specialty chemicals without harsh chemical catalysts. This will be of immediate interest and benefit to other scientists studying these catalysts. In the longer term, it should be of benefit and interest to specialty chemical manufacturers and paper and pulp processors and manufacturers.
Technical Abstract: The action of Streptomyces lividans acetylxylan esterase on methyl 2,4-di-O-acetyl- and 3,4-di-O-acetyl beta-D-xylopyranoside was compared with its action on the 2- and 3-deoxy and 2- and 3-deoxy-fluoro-analogues of the two diacetates in order to elucidate the role of the free hydroxyl group in the rapid deacetylation of position 2 and 3 in the two first diacetates. The replacement of the hydroxyl group at position 2 or 3 resulted in a striking reduction of the rate of deacetylation of position 2 or 3. In all four substrate analogues, similarly as in the methyl beta-D-xylopyranoside diacetates, the enzyme deacetylated almost exclusively position 2 or 3. The position of deacetylation was found independent on the prevailed conformation of the substrates in solution as determined by 1H-NMR spectroscopy. 4-Mono-O-acetyl derivatives were the major products of the first deacetylation. These observations are consistent with our earlier hypothesis that the deacetylation of position 2 and 3 may involve a common orthoester intermediate. Other possible roles of the free vicinal hydroxyl group could be an activation of the ester carbonyl group in the deacetylation mechanism. The involvement of the free hydroxyl group in the substrate binding did not find support in the results of inhibition experiments in which methyl 2,4-di-O-acetyl beta-D-xylopyranoside and 3-deoxy-2,4-di-O-acetyl beta-D-xylopyranoside were used as substrates and methyl beta-D-xylopyranoside as inhibitor. The enzyme requires for its action the trans arrangement of the free and acetylated hydroxyl groups at positions 2 and 3.