Evolutionary history and activity towards oligosaccharides and polysaccharides of GH3 glycosidases from an Antarctic marine bacterium.

Glycoside hydrolases (GHs) are pivotal in the hydrolysis of the glycosidic bonds of sugars, which are the main carbon and energy sources. The genome of Marinomonas sp. ef1, an Antarctic bacterium, contains three GHs belonging to family 3. These enzymes have distinct architectures and low sequence identity, suggesting that they originated from separate horizontal gene transfer events. M-GH3&#95;A and M-GH3&#95;B, were found to differ in cold adaptation and substrate specificity. M-GH3&#95;A is a bona fide cold-active enzyme since it retains 20 % activity at 10 °C and exhibits poor long-term thermal stability. On the other hand, M-GH3&#95;B shows mesophilic traits with very low activity at 10 °C (< 5 %) and higher long-term thermal stability. Substrate specificity assays highlight that M-GH3&#95;A is a promiscuous β-glucosidase mainly active on cellobiose and cellotetraose, whereas M-GH3&#95;B is a β-xylosidase active on xylan and arabinoxylan. Structural analysis suggests that such functional differences are due to their differently shaped active sites. The active site of M-GH3&#95;A is wider but has a narrower entrance compared to that of M-GH3&#95;B. Genome-based prediction of metabolic pathways suggests that Marinomonas sp. ef1 can use monosaccharides derived from the GH3-catalyzed hydrolysis of oligosaccharides either as a carbon source or for producing osmolytes.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests. Marco Mangiagalli reports financial support was provided by University of Milano-Bicocca. Marina Lotti reports financial support was provided by University of Milano-Bicocca. Salvatore Fusco reports financial support was provided by University of Verona. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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