Maturation of copper- and nickel-containing enzymes relies on a battery of metallochaperones, which play an important role in the transport and trafficking of Cu or Ni, and assist the assembly of metallocenter in metalloenzymes. Significant progress on the structure and function of metallochaperones has been made in the past years, improving our understanding on the homeostasis of Cu/Ni in cells. Recent progress of Cu/Ni chaperones is summarized in this review. The blueprint of Cu import and homeostasis is briefly discussed followed by the structural and functional aspects of selected Cu chaperones, i.e. Atox1, Cox17 and CCS. Moreover, the putative relationships between Cu chaperones and drugs are discussed. The second part focuses on the maturation of hydrogenase and urease, in which a series of Ni chaperones interacts with each other to achieve the homeostasis of nickel. Selected structural complexes and in vivo functional study of the chaperones are emphasized, the “cross-talk” between the two maturation pathways is presented.

Contents
1 Introduction
2 Copper chaperones
2.1 Cu import and homeostasis
2.2 Atox1
2.3 Cox17
2.4 CCS
2.5 Copper chaperones in relation to drugs
3 Nickel chaperones
3.1 Ni importer, regulator and storage
3.2 Ni chaperones for the maturation of urease
3.3 Ni chaperones for the maturation of hydrogenase
3.4 Cross-talk between the maturation of urease and hydrogenase
4 Conclusion