Metalation and activation of Zn 2+ enzymes via early secretory pathway-resident ZNT proteins.

Zinc (Zn 2+ ), an essential trace element, binds to various proteins, including enzymes, transcription factors, channels, and signaling molecules and their receptors, to regulate their activities in a wide range of physiological functions. Zn 2+ proteome analyses have indicated that approximately 10% of the proteins encoded by the human genome have potential Zn 2+ binding sites. Zn 2+ binding to the functional site of a protein (for enzymes, the active site) is termed Zn 2+ metalation. In eukaryotic cells, approximately one-third of proteins are targeted to the endoplasmic reticulum; therefore, a considerable number of proteins mature by Zn 2+ metalation in the early secretory pathway compartments. Failure to capture Zn 2+ in these compartments results in not only the inactivation of enzymes ( apo -Zn 2+ enzymes), but also their elimination via degradation. This process deserves attention because many Zn 2+ enzymes that mature during the secretory process are associated with disease pathogenesis. However, how Zn 2+ is mobilized via Zn 2+ transporters, particularly ZNTs, and incorporated in enzymes has not been fully elucidated from the cellular perspective and much less from the biophysical perspective. This review focuses on Zn 2+ enzymes that are activated by Zn 2+ metalation via Zn 2+ transporters during the secretory process. Further, we describe the importance of Zn 2+ metalation from the physiopathological perspective, helping to reveal the importance of understanding Zn 2+ enzymes from a biophysical perspective.