PMID: 30644839

Authors:

Agirre J, Moroz O, Meier S, Brask J, Munch A, Hoff T, Andersen C, Wilson KS, Davies GJ

Title:

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

Journal:

Acta Crystallogr D Struct Biol. 2019 Jan 1;75(Pt 1):1-7. doi:, 10.1107/S2059798318014900. Epub 2019 Jan 4.

Abstract:

alpha-Amylases are glycoside hydrolases that break the alpha-1,4 bonds in starch and related glycans. The degradation of starch is rendered difficult by the presence of varying degrees of alpha-1,6 branch points and their possible accommodation within the active centre of alpha-amylase enzymes. Given the myriad industrial uses for starch and thus also for alpha-amylase-catalysed starch degradation and modification, there is considerable interest in how different alpha-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 alpha-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 A resolution. Limit digest analysis by two-dimensional NMR using both pullulan (a regular linear polysaccharide of alpha-1,4, alpha-1,4, alpha-1,6 repeating trisaccharides) and amylopectin starch showed how the Alicyclobacillus sp. enzyme could accept alpha-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.