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The structure of the AliC GH13 α-amylase from Alicyclobacillus sp. reveals the accommodation of starch branching points in the α-amylase family

DOI: 10.1107/S2059798318014900 DOI Help

Authors: Jon Agirre (The University of York) , Olga Moroz (The University of York) , Sebastian Meier (University of Denmark) , Jesper Brask (Novozymes A/S) , Astrid Munch (Novozymes A/S) , Tine Hoff (Novozymes A/S) , Carsten Andersen (Novozymes A/S) , Keith S. Wilson (University of York) , Gideon J. Davies (The University of York)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Acta Crystallographica Section D Structural Biology , VOL 75 , PAGES 1 - 7

State: Published (Approved)
Published: January 2019
Diamond Proposal Number(s): 7864 , 9948

Open Access Open Access

Abstract: α-Amylases are glycoside hydrolases that break the α-1,4 bonds in starch and related glycans. The degradation of starch is rendered difficult by the presence of varying degrees of α-1,6 branch points and their possible accommodation within the active centre of α-amylase enzymes. Given the myriad industrial uses for starch and thus also for α-amylase-catalysed starch degradation and modification, there is considerable interest in how different α-amylases might accommodate these branches, thus impacting on the potential processing of highly branched post-hydrolysis remnants (known as limit dextrins) and societal applications. Here, it was sought to probe the branch-point accommodation of the Alicyclobacillus sp. CAZy family GH13 α-amylase AliC, prompted by the observation of a molecule of glucose in a position that may represent a branch point in an acarbose complex solved at 2.1 Å resolution. Limit digest analysis by two-dimensional NMR using both pullulan (a regular linear polysaccharide of α-1,4, α-1,4, α-1,6 repeating trisaccharides) and amylopectin starch showed how the Alicyclo­bacillus sp. enzyme could accept α-1,6 branches in at least the −2, +1 and +2 subsites, consistent with the three-dimensional structures with glucosyl moieties in the +1 and +2 subsites and the solvent-exposure of the −2 subsite 6-hydroxyl group. Together, the work provides a rare insight into branch-point acceptance in these industrial catalysts.

Journal Keywords: AliC GH13 α-amylase; starch branching points; glycoside hydrolases; pullulan; carbohydrate-active enzymes; Alicyclobacillus

Subject Areas: Biology and Bio-materials

Instruments: I04-Macromolecular Crystallography