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    Author(s): Vera Novy; Kevin Aïssa; Fredrik Nielsen; Suzana K. Straus; Peter Ciesielski; Christopher G. Hunt; Jack Saddler
    Date: 2019
    Source: Proceedings of the National Academy of Sciences. 116(45): 22545-22551.
    Publication Series: Scientific Journal (JRNL)
    Station: Forest Products Laboratory
    PDF: Download Publication  (2.0 MB)

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    Two fluorescence-tagged carbohydrate-binding modules (CBMs), which specifically bind to crystalline (CBM2a-RRedX) and paracrystalline (CBM17-FITC) cellulose, were used to differentiate the supramolecular cellulose structures in bleached softwood Kraft fibers during enzyme-mediated hydrolysis. Differences in CBM adsorption were elucidated using confocal laser scanning microscopy (CLSM), and the structural changes occurring during enzymemediated deconstruction were quantified via the relative fluorescence intensities of the respective probes. It was apparent that a high degree of order (i.e., crystalline cellulose) occurred at the cellulose fiber surface, which was interspersed by zones of lower structural organization and increased cellulose accessibility. Quantitative image analysis, supported by 13C NMR, scanning electron microscopy (SEM) imaging, and fiber length distribution analysis, showed that enzymatic degradation predominates at these zones during the initial phase of the reaction, resulting in rapid fiber fragmentation and an increase in cellulose surface crystallinity. By applying this method to elucidate the differences in the enzyme-mediated deconstruction mechanisms, this work further demonstrated that drying decreased the accessibility of enzymes to these disorganized zones, resulting in a delayed onset of degradation and fragmentation. The use of fluorescence-tagged CBMs with specific recognition sites provided a quantitative way to elucidate supramolecular substructures of cellulose and their impact on enzyme accessibility. By designing a quantitative method to analyze the cellulose ultrastructure and accessibility, this study gives insights into the degradation mechanism of cellulosic substrates.

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    Novy, Vera; Aïssa, Kevin; Nielsen, Fredrik; Straus, Suzana K.; Ciesielski, Peter; Hunt, Christopher G.; Saddler, Jack. 2019. Quantifying cellulose accessibility during enzyme-mediated deconstruction using 2 fluorescence-tagged carbohydrate-binding modules. Proceedings of the National Academy of Sciences. 116(45): 22545-22551.


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    Carbohydrate-binding modules, enzyme accessibility, supramolecular cellulose structure, confocal laser scanning microscopy, quantitative image analysis

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