The Ni(II)-binding properties of the metallochaperone SlyD.

Metallochaperones are essential for the safe and targeted delivery of necessary yet toxic metal cofactors to their respective protein partners. In this study we examine the nickel-binding properties of the Escherichia coli protein SlyD, a factor that contributes to optimal nickel accumulation in this organism. This protein is also required for E. coli energy metabolism because it participates in the nickel insertion step during [Ni−Fe]-hydrogenase metallocenter assembly. Our study demonstrates that SlyD is a multiple nickel ion binding protein. The analysis of noncovalent metal−protein complexes via electrospray ionization mass spectrometry revealed that SlyD binds up to seven nickel ions in a noncooperative manner with submicromolar affinity (<2 μM, upper limit) and that the protein exists in a dynamic mixture of metalloforms that is dependent on the availability of nickel ions in solution. Structural analysis indicates that this metallochaperone undergoes small but distinct changes in the structure upon...