Differences in the binding of sulfate, selenate and thiosulfate ions to bovine liver rhodanese, and a description of a binding site for ammonium and sodium ions. An X-ray diffraction study.
The binding of sulfate, selenate and thiosulfate by the sulfur-transferase rhodanese (EC 2.8.1.1) in the crystalline state has been studied by X-ray analysis at resolutions between 0.23 nm and 0.4 nm. The three ions appear to occupy a common site between the N eta atoms of Arg-29 and the main-chain NH group of Glu-148 at the surface of the enzyme molecule. A second binding site for the three ions is situated at the entrance to the active centre, between the side chains of Arg-186 and Lys-249. Selenate and thiosulfate are bound equally well at both anion-binding sites. Sulfate, however, binds better at the first position, near Arg-29, than at the second site near Arg-186. In the complex of sulfur-rhodanese with thiosulfate, the outer sulfur atom of the anion near the active centre points towards the extra sulfur atom which is bound as a persulfide to the S gamma of the essential Cys-247. The distance between the outer sulfur atom of the thiosulfate ion and the persulfide sulfur atom appears to be about 0.3 nm. The thiosulfate difference Fourier also shows a distinct, localized conformational change involving residues 71, 72 and 249. This is the result of the replacement of an ammonium ion in the sulfate and selenate media by a sodium ion in the sodium thiosulfate solution. Rhodanese is apparently able to accomodate ions with different radii at this cation-binding site by minor structural alterations.
D000645:Ammonium Sulfate / Q000378:metabolism; D000818:Animals; D000838:Anions; D001120:Arginine; D001665:Binding Sites; D002414:Cations, Monovalent; D002417:Cattle; D003545:Cysteine; D008099:Liver / Q000201:enzymology*; D064586:Selenic Acid; D012643:Selenium / Q000378:metabolism*; D018036:Selenium Compounds; D012964:Sodium / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism*; D013455:Sulfur; D013466:Sulfurtransferases / Q000378:metabolism*; D013884:Thiosulfate Sulfurtransferase / Q000378:metabolism*; D013885:Thiosulfates / Q000378:metabolism*; D014961:X-Ray Diffraction
D000838:Anions; D002414:Cations, Monovalent; D018036:Selenium Compounds; D013431:Sulfates; D013885:Thiosulfates; D013455:Sulfur; D001120:Arginine; D012964:Sodium; D013466:Sulfurtransferases; D013884:Thiosulfate Sulfurtransferase; D012643:Selenium; D064586:Selenic Acid; D003545:Cysteine; D000645:Ammonium Sulfate