Structural features of a Bacteroidetes-affiliated cellulase linked with a polysaccharide utilization locus
| Autor: | Alasdair Mackenzie, Bj Dalhus, Adrian E. Naas, Phillip B. Pope, Vincent G. H. Eijsink |
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| Jazyk: | angličtina |
| Rok vydání: | 2015 |
| Předmět: | |
| Zdroj: | 'Scientific Reports ', vol: 5, pages: 11666-1-11666-12 (2015) Scientific Reports |
| ISSN: | 2045-2322 |
| Popis: | Previous gene-centric analysis of a cow rumen metagenome revealed the first potentially cellulolytic polysaccharide utilization locus, of which the main catalytic enzyme (AC2aCel5A) was identified as a glycoside hydrolase (GH) family 5 endo-cellulase. Here we present the 1.8 Å three-dimensional structure of AC2aCel5A and characterization of its enzymatic activities. The enzyme possesses the archetypical (β/α)8-barrel found throughout the GH5 family and contains the two strictly conserved catalytic glutamates located at the C-terminal ends of β-strands 4 and 7. The enzyme is active on insoluble cellulose and acts exclusively on linear β-(1,4)-linked glucans. Co-crystallization of a catalytically inactive mutant with substrate yielded a 2.4 Å structure showing cellotriose bound in the −3 to −1 subsites. Additional electron density was observed between Trp178 and Trp254, two residues that form a hydrophobic “clamp”, potentially interacting with sugars at the +1 and +2 subsites. The enzyme’s active-site cleft was narrower compared to the closest structural relatives, which in contrast to AC2aCel5A, are also active on xylans, mannans and/or xyloglucans. Interestingly, the structure and function of this enzyme seem adapted to less-substituted substrates such as cellulose, presumably due to the insufficient space to accommodate the side-chains of branched glucans in the active-site cleft. |
| Databáze: | OpenAIRE |
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