Oligosaccharide substrate binding in Escherichia coli maltodextrin phosphorylase.
The crystal structure of E. coli maltodextrin phosphorylase co-crystallized with an oligosaccharide has been solved at 3.0 A resolution, providing the first structure of an oligosaccharide bound at the catalytic site of an alpha-glucan phosphorylase. An induced fit mechanism brings together two domains across the catalytic site tunnel. A stacking interaction between the glucosyl residue and the aromatic group of a tyrosine residue at a sub-site remote (8 A) from the catalytic site provides a key element in substrate recognition; mutation of this residue to Ala decreases the Kcat/Km by 10(4). Extrapolation of the results to substrate binding across the site of attack by phosphorolysis indicates a likely alteration in the glycosidic torsion angles from their preferred values, an alteration that appears to be important for the catalytic mechanism.
O'Reilly
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Laboratory of Molecular Biophysics, University of Oxford.
Watson
K A
KA
Schinzel
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R
Palm
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Johnson
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LN
D003460:Crystallization; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology*; D005936:Glucans / Q000737:chemistry / Q000378:metabolism; D005964:Glucosyltransferases / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D009844:Oligosaccharides / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D014443:Tyrosine / Q000502:physiology
D005936:Glucans; D009844:Oligosaccharides; C016549:maltohexaose; C031146:maltoheptaose; D014443:Tyrosine; D005964:Glucosyltransferases; C033938:maltodextrin phosphorylase