The SufE Protein and the SufBCD Complex Enhance SufS Cysteine Desulfurase Activity as Part of a Sulfur Transfer Pathway for Fe-S Cluster Assembly in Escherichia coli

The sufABCDSE operon of the Gram-negative bacterium Escherichia coli is induced by oxidative stress and iron deprivation. To examine the biochemical roles of the Suf proteins, we purified all of the proteins and assayed their effect on SufS cysteine desulfurase activity. Here we report that the SufE protein can stimulate the cysteine desulfurase activity of the SufS enzyme up to 8-fold and accepts sulfane sulfur from SufS. This sulfur transfer process from SufS to SufE is sheltered from the environment based on its resistance to added reductants and on the analysis of available crystal structures of the proteins. We also found that the SufB, SufC, and SufD proteins associate in a stable complex and that, in the presence of SufE, the SufBCD complex further stimulates SufS activity up to 32-fold. Thus, the SufE protein and the SufBCD complex act synergistically to modulate the cysteine desulfurase activity of SufS. We propose that this sulfur transfer mechanism may be important for limiting sulfide release during oxidative stress conditions in vivo.