Abstract
The Acetivibrio clariflavus (basonym: Clostridium clariflavum) glycoside hydrolase family 30 cellulosomal protein encoded by the Clocl_1795 gene was highly represented during growth on cellulosic substrates. In this report, the recombinantly expressed protein has been characterized and shown to be a non-reducing terminal (NRT)-specific xylobiohydrolase (AcXbh30A). Biochemical function, optimal biophysical parameters, and phylogeny were investigated. The findings indicate that AcXbh30A strictly cleaves xylobiose from the NRT up until an α-1,2-linked glucuronic acid (GA)-decorated xylose if the number of xyloses is even or otherwise a single xylose will remain resulting in a penultimate GA-substituted xylose. Unlike recently reported xylobiohydrolases, AcXbh30A has no other detectable hydrolysis products under our optimized reaction conditions. Sequence analysis indicates that AcXbh30A represents a new GH30 subfamily. This new xylobiohydrolase may be useful for commercial production of industrial quantities of xylobiose.
Highlights
The most abundant hemicellulose, xylan, represents the second most plentiful terrestrial polysaccharide on earth (Saha, 2003)
The AcXbh30A enzyme was first identified following its proteomic detection as a major protein component of the A. clariflavus cellulosome during cultivation on cellulosic substrates (Artzi et al, 2015)
Suspecting this to have resulted from proteolytic processing, we generated two constructs of AcXbh30A by cloning with a His-tag appended to the C-terminus of a full-length construct and to a catalytic domain (CD) only construct
Summary
The most abundant hemicellulose, xylan, represents the second most plentiful terrestrial polysaccharide on earth (Saha, 2003). Given its abundance, it has received significant consideration by industry and academia for utilization through bioconversion to green chemicals and fuels (Naidu et al, 2018) as well as for contributions to human health and wellbeing (Ebringerova and Hromadkova, 1999; Vazquez et al, 2000; Aachary and Prapulla, 2011; Chen et al, 2012; EFSA Panel on Dietetic Products et al, 2018). Both neutral oligoxylosides and aldouronates have potential value directly as either a nutraceutical or a functional food ingredient, a pharmacologically active compound, or pharmacological precursors (Ebringerova and Hromadkova, 1999; Vazquez et al, 2000; Ebringerová et al, 2002; Ohbuchi et al, 2010; Penksza et al, 2018)
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