Iron-binding activity of human iron-sulfur cluster assembly protein hIscA1

A human homologue of the iron-sulfur cluster assembly protein IscA (hIscA1) has been cloned and expressed in Escherichia coli cells. The UV-visible absorption and EPR (electron paramagnetic resonance) measurements reveal that hIscA1 purified from E. coli cells contains a mononuclear iron centre and that the iron binding in hIscA1 expressed in E. coli cells can be further modulated by the iron content in the cell growth medium. Additional studies show that purified hIscA1 binds iron with an iron association constant of approx. 2x1019 M-1, and that the iron-bound hIscA1 is able to provide the iron for the iron-sulfur cluster assembly in a proposed scaffold protein, IscU of E. coli, in vitro. The complementation experiments indicate that hIscA1 can partially substitute for IscA in restoring the cell growth of E. coli in the M9 minimal medium under aerobic conditions. The results suggest that hIscA1, like E. coli IscA, is an iron-binding protein that may act as an iron chaperone for biogenesis of iron-sulfur clusters.