Cysteine-Persulfide Sulfane Sulfur-Ligated Zn Complex of Sulfur-Carrying SufU in the SufCDSUB System for Fe-S Cluster Biosynthesis.

SufU, a component of the SufCDSUB Fe-S cluster biosynthetic system, serves as a Zn-dependent sulfur-carrying protein that delivers inorganic sulfur in the form of cysteine persulfide from SufS to SufBCD. To understand this sulfur delivery mechanism, we studied the X-ray crystal structure of SufU and its sulfur-carrying state (persulfurated SufU) and performed functional analysis of the conserved amino acid residues around the Zn sites. Interestingly, sulfur-carrying SufU with Cys41-persulfide (Cys41-S-S) exhibited a unique Zn coordination structure, in which electrophilic S is ligated to Zn and nucleophilic/anionic S is bound to distally conserved Arg125.