The Biosynthesis of the Molybdenum Cofactor in Escherichia coli and Its Connection to FeS Cluster Assembly and the Thiolation of tRNA
Figure 8
Sulfur transfer to sulfur-containing biomolecules involving the IscS-bound persulfide. A protein-bound persulfide group is formed on the L-cysteine desulfurase IscS, which is further transferred to proteins like IscU, TusA, or ThiI. CyaY and IscX were also shown to bind to IscS. IscU is the primary scaffold for the assembly of FeS clusters. The IscS sulfur can also be further transferred for the thiolation of tRNA. In E. coli tRNA modification can be divided into an FeS cluster independent pathway and into a pathway which requires FeS clusters. The synthesis of s2C by TtcA and ms2i6A by MiaB require sulfur from the FeS clusters initially formed on IscU. ThiI can transfer sulfur either for the formation of thiamine or for the formation of s4U in tRNA. TusA can transfer sulfur for a sulfur relay system involving TusBCD, TusE, and MnmA for the formation of s2U in tRNA, or additionally TusA is involved in sulfur transfer for Moco biosynthesis. Persulfide-containing proteins are highlighted in red and names of the final sulfur-containing molecules are colored in blue.
