Abstact

Copper trafficking proteins and copper-sensitive regulators are often found to be able to bind multiple Cu(I) ions in the form of Cu(I) clusters. We have determined the high-resolution X-ray crystal structure of an Atx1-like copper chaperone protein from Bacillus subtilis containing a novel tetranuclear Cu(I) cluster. The identities and oxidation states of the cluster ions were established unambiguously by refinement of X-ray energy-dependent anomalous scattering factors. The [Cu(4)(S-Cys)(4)(N-His)(2)] cluster geometry provides new structural insights into not only the binding of multiple cuprous ions by metallochaperones but also protein-associated tetranuclear Cu(I) clusters, including those found in eukaryotic copper-responsive transcription factors.