Crystal structure of the iron-sulfur cluster transfer protein ApbC from Escherichia coli

Iron-sulfur (Fe-S) clusters are ubiquitous and are necessary to sustain basic life processes. The intracellular Fe-S clusters do not form spontaneously and many proteins are required for their biosynthesis and delivery. The bacterial P-loop NTPase family protein ApbC participates in Fe-S cluster assembly and transfers the cluster into apoproteins, with the Walker A motif and CxxC motif being essential for functionality of ApbC in Fe-S protein biogenesis. However, the structural basis underlying the ApbC activity and the motifs’ role remains unclear. Here, we report the crystal structure of Escherichia coli ApbC at 2.8-Å resolution. The dimeric structure is in a W shape and the active site is located in the 2-fold center. The function of the motifs can be annotated by structural analyses. ApbC has an additional N-terminal domain that differs from other P-loop NTPases, possibly conferring its inherent specificity in vivo.