HscB is a 235 amino acid mitochondrial protein that functions as a co-chaperone in iron-sulfur cluster formation. Highly expressed in heart, liver and muscle, and belonging to the HscB family, HscB exists as a L-shaped crystal structure resembling E. coli HscB. Human HscB contains an N-terminal mitochondrial targeting signal followed by a J-domain and short loop. The C-terminal domain folds into a compact 3-helix bundle and likely mediates specific interactions with IscU. Containing six exons and five introns, the gene encoding HscB maps to human chromosome 22, which houses over 500 genes and is the second smallest human chromosome.