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

Jon Agirre, Olga Moroz, Sebastian Meier, Jesper Brask, Astrid Munch, Tine Hoff, Carsten Andersen, Keith S Wilson, Gideon J Davies

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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.

Original languageEnglish
Pages (from-to)1-7
Number of pages7
JournalActa crystallographica. Section D, Structural biology
Issue number1
Publication statusPublished - 1 Jan 2019


  • AliC GH13 α-amylase
  • Alicyclobacillus
  • carbohydrate-active enzymes
  • glycoside hydrolases
  • pullulan
  • starch branching points

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