Abstract
Thiamine pyrophosphate is a required coenzyme that contains a mechanistically important sulfur atom. In Salmonella enterica, sulfur is trafficked to both thiamine biosynthesis and 4-thiouridine biosynthesis by the enzyme ThiI using persulfide (R-S-S-H) chemistry. It was previously reported that a thiI mutant strain could grow independent of exogenous thiamine in the presence of cysteine, suggesting there was a second mechanism for sulfur mobilization. Data reported here show that oxidation products of cysteine rescue the growth of a thiI mutant strain by a mechanism that requires the transporter YdjN and the cysteine desulfhydrase CdsH. The data are consistent with a model in which sulfide produced by CdsH reacts with cystine (Cys-S-S-Cys), S-sulfocysteine (Cys-S-SO3 (-)), or another disulfide to form a small-molecule persulfide (R-S-S-H). We suggest that this persulfide replaced ThiI by donating sulfur to the thiamine sulfur carrier protein ThiS. This model describes a potential mechanism used for sulfur trafficking in organisms that lack ThiI but are capable of thiamine biosynthesis.