4B9Z: Crystal Structure Of Agd31b, Alpha-transglucosylase, Complexed With Acarbose

Citation:
Abstract
The metabolism of the storage polysaccharides glycogen and starch is of vital importance to organisms from all domains of life. In bacteria, utilization of these alpha-glucans requires the concerted action of a variety of enzymes, including glycoside hydrolases, glycoside phosphorylases, and transglycosylases. In particular, transglycosylases from glycoside hydrolase family 13 (GH13) and GH77 play well established roles in alpha-glucan side chain (de)branching, regulation of oligo- and polysaccharide chain length, and formation of cyclic dextrans. Here, we present the biochemical and tertiary structural characterization of a new type of bacterial 1,4-alpha-glucan 4-alpha-glucosyltransferase from GH31. Distinct from 1,4-alpha-glucan 6-alpha-glucosyltransferases (EC 2.4.1.24) and 4-alpha-glucanotransferases (EC 2.4.1.25), this enzyme strictly transferred one glucosyl residue from alpha(1-->4)-glucans in disproportionation reactions. Substrate hydrolysis was undetectable for a series of malto-oligosaccharides except maltose for which transglycosylation nonetheless dominated across a range of substrate concentrations. Crystallographic analysis of the enzyme in free, acarbose-complexed, and trapped 5-fluoro-beta-glucosyl-enzyme intermediate forms revealed extended substrate interactions across one negative and up to three positive subsites, thus providing structural rationalization for the unique, single monosaccharide transferase activity of the enzyme.
PDB ID: 4B9ZDownload
MMDB ID: 104999
PDB Deposition Date: 2012/9/9
Updated in MMDB: 2012/12
Experimental Method:
x-ray diffraction
Resolution: 2  Å
Source Organism:
Similar Structures:
Biological Unit for 4B9Z: monomeric; determined by author and by software (PISA)
Molecular Components in 4B9Z
Label Count Molecule
Protein (1 molecule)
1
Alpha-glucosidase, Putative, Adg31b
Molecule annotation
Chemicals (23 molecules)
1
1
2
5
3
1
4
1
5
15
* Click molecule labels to explore molecular sequence information.

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