Metal ions are commonly seen in naturally occurring protein molecules, and often play pivotal roles in protein function. Deepening understanding of basic coordination models between amino acids and various metals facilitates artificial designs of novel peptide-metal coordination modalities that can be broadly applied in research fields such as peptide structure-function optimization, molecular assembly, labeling and imaging, and peptide therapeutics development. This minireview introduces the basic coordination chemistry between electron-donating groups on peptides (namely carboxylate, amine, imidazole, sulfhydryl groups) and their respective favorable metal ions with illustrated examples. We next discuss in detail the use of metal or metalloid coordination in fundamental research of peptides and proteins, including secondary structure constraining, supermolecular assembly, fluorescence or phosphorescence labeling, and protein folding analysis. In particular, we highlight two examples of luminogenic peptide/protein labeling techniques, the first being the broadly applied biarsenical ligand and tetracysteine motif based protein probing method, and the second being the recently reported iridium(Ⅲ) complex and histidine motif based peptide labeling technique. Finally we discuss the principles in the development of metallo-peptide molecular probes and the potential brought by this research for optimization in drug designs.

Contents
1 Introduction
2 Common binding groups in peptides for metal coordination
2.1 Carboxyl group
2.2 Amine group and imidazole group
2.3 Sulfhydryl group
3 The effects of metal coordination on peptide/protein structure
3.1 Folding and stabilization
3.2 Supermolecular assembly
4 Coordination-based peptide luminescent labeling and biological applications
5 Outlook