Structural biology of starch-degrading enzymes and their regulation

Abstract

Starch is a major energy source for all domains of life. Recent advances in structures of starch-degrading enzymes encompass the substrate complex of starch debranching enzyme, the function of surface binding sites in plant isoamylase, details on individual steps in the mechanism of plant disproportionating enzyme and a self-stabilised conformation of amylose accommodated in the active site of plant a-glucosidase.Important inhibitor complexes include a flavonol glycoside, montbretin A, binding at the active site of human pancreatic a-amylase and barley limit dextrinase inhibitor binding to the debranching enzyme, limit dextrinase using a new binding mode for cereal protein inhibitors.

Arabidopsis β-Amylase2 Is a K+-Requiring, Catalytic Tetramer with Sigmoidal Kinetics

“…The BAM5 ortholog from sweet potato was crystallized as a homotetramer, but that enzyme did not exhibit cooperative kinetics and the protein was active as a monomer (Cheong et al, 1995). SBSs are found on some polysaccharide-active enzymes (Møller and Svensson, 2016), where they can serve a variety of functions, including localizing the enzyme near its substrate, guiding the substrate into the active site, enhancing processivity, or causing allosteric regulation (Cuyvers et al, 2012). A crystallized b-amylase from Bacillus cereus var mycoides was shown to contain a C-terminal carbohydrate-binding module (CBM) and several SBSs.…”

“…SBSs are usually discovered by observing ligands bound to crystallized proteins (Møller and Svensson, 2016). Once a bound ligand is observed, a predicted SBS can then be confirmed using mutagenesis to disrupt ligand binding followed by activity or substrate-binding assays.…”

Structural basis for the flexible recognition of α‐glucan substrates by Bacteroides thetaiotaomicron SusG

“…Glycoside hydrolase family 13 (GH13) describes a large class of enzymes that target the α1,4‐ and α1,6‐ linkages in starch, pullulan and glycogen . GH13 includes not only amylases that hydrolyze the backbone of all α1,4‐linked glucan helices, but also pullulanases and neopullulanases that target α1,6‐ and α1,4‐glycosidic bonds, respectively, within mixed‐linkage structures .…”

Raw starch degrading α-amylases: an unsolved riddle

“…Structure of twenty three different α-amylases have been determined [15] including recently published structures of a variant 'Termamyl-like' Geobacillus stearothermophilus α-amylase [36] and the α-amylase from Oryza sativa [37] from GH13 family.…”

“…One recent review deals specifically with published data for ethanol production by cold hydrolysis of starchy raw materials [10]. Novel findings on functional structural relations of enzymes naturally involved in starch degradation have also been reviewed [15]. Due to importance of α-amylases for the hydrolysis of α-1,4-glycosidic bonds of raw starch and since the majority of known RSDE belong to the α-amylase family, in this article we will focus primarily on recent advances in the production and downstream processing, sequence characterization, biochemical properties, and application of raw starch degrading α-amylases (RSDA) from GH13 family.…”