Structural ratio-rials for the short branched substrato soscificity of the glycogen debranching enzyme GlgX

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Title
Structural ratio-rials for the short branched substrato soscificity of the glycogen debranching enzyme GlgX
Author(s)
Hyung Nam Song; Tae Yang Jung; J T Park; Byoung Chul Park; P K Myung; W Boos; Eui-jeon Woo; K H Park
Bibliographic Citation
Proteins-Structure Function and Bioinformatics, vol. 78, no. 8, pp. 1847-1855
Publication Year
2010
Abstract
Glycogen serves as major energy storage in most living organisms. GlgX, with its gene in the glycogen degradation operon, functions in glycogen catabolism by selectively catalyzing the debranching of polysaccharide outer chains in bacterial glycosynthesis. GlgX hydrolyzes α-1,6glycosidic linkages of phosphorylase-limit dextrin containing only three or four glucose subunits produced by glycogen Phosphorylase. To understand its mechanism and unique substrate specificity toward short branched α-polyglucans, we determined the structure of GlgX from Escherichia Coli K12 at 2.25 A resolution. The structure reveals a monomer consisting of three major domains with high structural similarity to the subunit of TreX, the oligomeric bifunctional glycogen debranching enzyme (GDE) from Sulfolobus. In the overlapping substrate binding groove, conserved residues Leu270, Asp271, and Pro208 block the cleft, yielding a shorter narrow GIgX cleft compared to that of TreX. Residues 207-213 form a unique helical conformation that is observed in both GIgX and TreX, possibly distinguishing GDEs from isoamylases and pullulanases. The structural feature observed at the substrate binding groove provides a molecular explanation for the unique substrate specificity of GlgX for G4 phosphorylase-limit dextrin and the discriminative activity of TreX and GlgX toward substrates of varying lengths.
Keyword
GDEGlgXGlycogen catabolismMalto-oligosaccharidesX-ray structure
ISSN
0887-3585
Publisher
Wiley
DOI
http://dx.doi.org/10.1002/prot.22697
Type
Article
Appears in Collections:
Division of Biomedical Research > Disease Target Structure Research Center > 1. Journal Articles
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