Steve Ealick's Research Group

Amycolatopsis orientalis BexX-CysO

PDB file:



The ability of BexX to selectively distinguish sulphur carrierproteins was given a structural basis in this work. This study was, to our knowledge, the first complete characterization of thiosugar formation in nature. It also demonstrates the receptor promiscuity of theA. orientalis sulphur-delivery system. BexX,has a protein sequence
and mode of action are similar to those of ThiG, which catalyzes thiazole formation in thiamine biosynthesis.

The BexX-CysO protomer has the CysO bonded such that its CysO, the sulfur carrier protein, is positioned to insert its C terminal tail into the active site of its partner. CysO contributes19 residues and BexX contributes 26 residues to the BexX–CysO interface.

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The BexX–CysO heterodimer is formed by crystallographic twofold symmetry, with a BexX dimer core. Each CysO is bonded to a BexX at a similar exterior position so they are far from each other. The arrangement is very similar to that of the ThiG-ThiS interface.

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The active site of BexX was identified by crystallization with reactant glucose-6-phosphate, which is converted to 2-thioglucose.

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Sasaki E, Zhang X, Sun HG, Lu MY, Liu TL, Ou A, Li JY, Chen YH, Ealick SE, and Liu HW. Co-opting sulphur-carrier proteins from primary metabolic pathways for 2-thiosugar biosynthesis. Nature 510:427-431 (2014). PubMed

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