In nature, nontoxic protein amyloids serve as dynamic, protein-specific depots, exemplified by both bacterial inclusion bodies and secretory granules from the endocrine system. Inspired by these systems, chemically defined and regulatory-compliant artificial protein microgranules have been developed for clinical applications as endocrine-like protein repositories. This has been achieved by exploiting the reversible coordination between histidine residues and divalent cations such as Zn