Structural insights on starch hydrolysis by plant β-amylase and its evolutionary relationship with bacterial enzymes

International Journal of Biological Macromolecules
S VajravijayanK Gunasekaran

Abstract

The conversion of starch to maltose is catalysed in plants by β-amylase. The enzymatic mechanism has been well-characterized for the soybean and barley enzymes, which utilise a glutamic acid-glutamate pair. In the present study, we present a surprise observation of maltotetraose at the active site, the presence of which elucidates the clear role of Thr344 as a conformational "switch" between substrate binding and product release during hydrolysis. This observation is confirmed by the selection of maltotetraose by the crystallized enzyme although that carbohydrate was present in only trace amounts. The conformation of the residues in the substrate-binding site changed upon substrate binding, leading to the movement of threonine, glutamic acid, and the loop conformation, elucidating a missing link in the existing mechanism. By aligning our substrate-free and maltotetraose-bound structures with other existing structures, the sequence of events from substrate binding to hydrolysis can be visualized. Apart from this, the evolutionary relationship among β-amylases of bacterial and amyloplastic origin could be established. The presence of a sugar-binding domain in the bacterial enzyme and its absence in the plant counterpart could be ...Continue Reading

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Citations

Oct 26, 2018·Molecules : a Journal of Synthetic Chemistry and Natural Product Chemistry·Xinhong LiangBenguo Liu
Jan 15, 2019·Preparative Biochemistry & Biotechnology·Xuguo DuanYue Huang
Aug 12, 2021·Molecular Biology Reports·Moupriya NagRina Rani Ray
Oct 19, 2021·Plant Physiology·Laure C DavidSamuel C Zeeman

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