Crystal structure of Escherichia coli SufC, an ABC-type ATPase component of the SUF iron–sulfur cluster assembly machinery

SufC is an ATPase component of the SUF machinery, which is involved in the biosynthesis of Fe–S clusters. To gain insight into the function of this protein, we have determined the crystal structure of Escherichia coli SufC at 2.5 Å resolution. Despite the similarity of the overall structure with ABC-ATPases (nucleotide-binding domains of ABC transporters), some key differences were observed. Glu171, an invariant residue involved in ATP hydrolysis, is rotated away from the nucleotide-binding pocket to form a SufC-specific salt bridge with Lys152. Due to this salt bridge, D-loop that follows Glu171 is flipped out to the molecular surface, which may sterically inhibit the formation of an active dimer. Thus, the salt bridge may play a critical role in regulating ATPase activity and preventing wasteful ATP hydrolysis. Furthermore, SufC has a unique Q-loop structure on its surface, which may form a binding site for its partner proteins, SufB and/or SufD.