期刊
BMC BIOCHEMISTRY
卷 16, 期 -, 页码 -出版社
BMC
DOI: 10.1186/s12858-015-0055-4
关键词
Bifidobacterium; Carbohydrate-binding module; Gut microbiota; Mannan; Probiotic bacteria; Surface plasmon resonance
资金
- FoSu grant from the Danish Strategic Research Council [2101-07-0105]
- Swedish Research School for Pharmaceutical Sciences
- Swedish Agency for Innovation Systems [2013-03024]
- Swedish Research Council for Environmental, Agricultural Sciences and Spatial Planning [213-2011-1620, 213-2014-1254]
- Swedish Foundation for Strategic Research [14-0046]
- Danish Council for Independent Research \ Natural Sciences [060208673B]
- Vinnova [2013-03024] Funding Source: Vinnova
Background: beta-Mannans are abundant and diverse plant structural and storage polysaccharides. Certain human gut microbiota members including health-promoting Bifidobacterium spp. catabolize dietary mannans. Little insight is available on the enzymology of mannan deconstruction in the gut ecological niche. Here, we report the biochemical properties of the first family 5 subfamily 8 glycoside hydrolase (GH5_8) mannanase from the probiotic bacterium Bifidobacterium animalis subsp. lactis Bl-04 (BlMan5_8). Results: BlMan5_8 possesses a novel low affinity carbohydrate binding module (CBM) specific for soluble mannan and displays the highest catalytic efficiency reported to date for a GH5 mannanase owing to a very high kcat (1828 +/- 87 s(-1)) and a low K-m (1.58 +/- 0.23 g.L-1) using locust bean galactomannan as substrate. The novel CBM of BlMan5_8 mediates increased binding to soluble mannan based on affinity electrophoresis. Surface plasmon resonance analysis confirmed the binding of the CBM10 to manno-oligosaccharides, albeit with slightly lower affinity than the catalytic module of the enzyme. This is the first example of a low-affinity mannan-specific CBM, which forms a subfamily of CBM10 together with close homologs present only in mannanases. Members of this new subfamily lack an aromatic residue mediating binding to insoluble cellulose in canonical CBM10 members consistent with the observed low mannan affinity. Conclusion: BlMan5_8 is evolved for efficient deconstruction of soluble mannans, which is reflected by an exceptionally low K-m and the presence of an atypical low affinity CBM, which increases binding to specifically to soluble mannan while causing minimal decrease in catalytic efficiency as opposed to enzymes with canonical mannan binding modules. These features highlight fine tuning of catalytic and binding properties to support specialization towards a preferred substrate, which is likely to confer an advantage in the adaptation to competitive ecological niches.
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