Structural and Biochemical Characterization of Staphylococcus aureus Cysteine Desulfurase Complex SufSU.

In this work, we provide the first in vitro characterization of two essential proteins from Staphylococcus aureus ( S . aureus ) involved in iron-sulfur (Fe-S) cluster biogenesis: the cysteine desulfurase SufS and the sulfurtransferase SufU. Together, these proteins form the transient SufSU complex and execute the first stage of Fe-S cluster biogenesis in the SUF-like pathway in Gram-positive bacteria. The proteins involved in the SUF-like pathway, such as SufS and SufU, are essential in Gram-positive bacteria since these bacteria tend to lack redundant Fe-S cluster biogenesis pathways. Most previous work characterizing the SUF-like pathway has focused on Bacillus subtilis ( B . subtilis ). We focus on the SUF-like pathway in S. aureus because of its potential to serve as a therapeutic target to treat S. aureus infections. Herein, we characterize S. aureus SufS ( Sa SufS) by X-ray crystallography and UV-vis spectroscopy, and we characterize S. aureus SufU ( Sa SufU) by a zinc binding fluorescence assay and small-angle X-ray scattering. We show that Sa SufS is a type II cysteine desulfurase and that Sa SufU is a Zn 2+ -containing sulfurtransferase. Additionally, we evaluated the cysteine desulfurase activity of the Sa SufSU complex and compared its activity to that of B. subtilis SufSU. Subsequent cross-species activity analysis reveals a surprising result: Sa SufS is significantly less stimulated by SufU than Bs SufS. Our results set a basis for further characterization of Sa SufSU as well as the development of new therapeutic strategies for treating infections caused by S. aureus by inhibiting the SUF-like pathway.