The crystal structure of Escherichia coli CsdE

Sulfur incorporations both in the biosynthesis of sulfur-containing cofactors and in the sulfur-modifications of certain tRNAs are all mediated by the sulfur initially delivered from the cysteine desulfurases. Sulfur generated as persulfide from cysteine is transferred to the sulfur acceptor protein to further allow delivery to the required steps within an enzymatic process. CsdA which is one of the three cysteine desulfurases identified in Escherichia coli transfers sulfur to the non Fe–S sulfur-acceptor CsdE, however, the consequence of CsdE accepted sulfur is mostly unknown. In this study, we report the 2.4 Å structure of free CsdE determined using X-ray crystallography, and compare the structure with the CsdE structure determined using NMR and also CsdE within the crystal CsdA–CsdE complex. Further analysis suggests that the positive electrostatic potential surfaces of CsdE may mediate interaction with a yet unidentified protein or possibly tRNA to deliver sulfur.