PMID:10722656
| Citation |
Palenchar, PM, Buck, CJ, Cheng, H, Larson, TJ and Mueller, EG (2000) Evidence that ThiI, an enzyme shared between thiamin and 4-thiouridine biosynthesis, may be a sulfurtransferase that proceeds through a persulfide intermediate. J. Biol. Chem. 275:8283-6 |
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| Abstract |
ThiI is an enzyme common to the biosynthetic pathways leading to both thiamin and 4-thiouridine in tRNA. Comparison of the ThiI sequence with protein sequences in the data bases revealed that the Escherichia coli enzyme contains a C-terminal extension displaying sequence similarity to the sulfurtransferase rhodanese. Cys-456 of ThiI aligns with the active site cysteine residue of rhodanese that transiently forms a persulfide during catalysis. We investigated the functional importance of this sequence similarity and discovered that, like rhodanese, ThiI catalyzes the transfer of sulfur from thiosulfate to cyanide. Mutation of Cys-456 to alanine impairs this sulfurtransferase activity, and the C456A ThiI is incapable of supporting generation of 4-thiouridine in tRNA both in vitro and in vivo. We therefore conclude that Cys-456 of ThiI is critical for activity and propose that Cys-456 transiently forms a persulfide during catalysis. To accommodate this hypothesis, we propose a general mechanism for sulfur transfer in which the terminal sulfur of the persulfide first acts as a nucleophile and is then transferred as an equivalent of S(2-) rather than S(0). |
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| Keywords |
Amino Acid Sequence; Bacterial Proteins; Cyanides/metabolism; Escherichia coli Proteins; Models, Chemical; Molecular Sequence Data; RNA, Transfer/metabolism; Sequence Homology, Amino Acid; Sulfides/metabolism; Sulfurtransferases/metabolism; Thiamine/biosynthesis; Thiosulfate Sulfurtransferase/metabolism; Thiosulfates/metabolism; Thiouridine/metabolism |
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