Contribution of cysteine desulfurase (NifS protein) to the biotin synthasereaction of Escherichia coli

The contribution of cysteine desulfurase, the NifS protein of Klebsiella pn eumoniae and the IscS protein of Escherichia coli, to the biotin synthase r eaction was investigated in in vitro and in vivo reaction systems with E. c oli. When the nifS and nifU genes of K. pneumoniae were coexpressed in E. c oli, NifS and NifU proteins in complex (NifU/S complex) and NifU monomer fo rms were observed. Both the NifU/S complex and the NifU monomer stimulated the biotin synthase reaction in the presence of L-cysteine in an in vitro r eaction system. The NifU/S complex enhanced the production of biotin from d ethiobiotin by the cells growing in an in vivo reaction system. Moreover, t he IscS protein of E. coli stimulated the biotin synthase reaction in the p resence of L-cysteine in the cell-free system. These results strongly sugge st that cysteine desulfurase participates in the biotin synthase reaction, probably by supplying sulfur to the iron-sulfur cluster of biotin synthase.