SufBCD

SufBCD is a protein complex consisting of the SufB, SufC, and SufD proteins that participates in the bacterial iron-sulfur (Fe-S) cluster assembly pathway known as the SUF system. It is encoded as part of the suf operon (often sufABCDSE) found in many bacteria, including Escherichia coli. The SUF system is especially important under conditions of oxidative stress or iron limitation, when the canonical ISC pathway is less active.

The complex comprises SufB and SufD, which provide scaffold functions, and the ATPase SufC, which supplies energy for cluster assembly through ATP hydrolysis. SufC belongs to the ABC ATPase family, and its activity is coupled to conformational changes within the SufBCD core. SufB contains a conserved cysteine residue that participates in persulfide chemistry; sulfur is initially mobilized by the cysteine desulfurase SufS in conjunction with SufE and transferred toward the SufBCD scaffold for incorporation into Fe-S clusters.

In the assembly process, cysteine provides sulfur via SufS/SufE, and iron is incorporated to form Fe-S clusters, which are then coordinated on the SufBCD scaffold and finally transferred to recipient apo-proteins, often via SufA as a carrier. The SufBCD complex thus acts as a central hub for cluster assembly, maturation, and trafficking of Fe-S clusters.

Expression of the suf operon is regulated by cellular iron status and oxidative stress signals, and the SUF pathway can function as an alternative to the ISC system when conditions are adverse. While essential for survival under stress in many bacteria, the exact composition and regulation can vary across species.