Metal-binding proteins are

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s or protein domains that chelate a metal ion. Binding of metal ions via chelation is usually achieved via

histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH3+ form under biological conditions), a carboxylic acid group (which is in the de ...

s or

cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometime ...

s. In some cases this is a necessary part of their

folding Fold, folding or foldable may refer to: Arts, entertainment, and media * ''Fold'' (album), the debut release by Australian rock band Epicure *Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot *Above ...

and maintenance of a

tertiary structure Protein tertiary structure is the three dimensional shape of a protein. The tertiary structure will have a single polypeptide chain "backbone" with one or more protein secondary structures, the protein domains. Amino acid side chains may int ...

. Alternatively, a metal-binding protein may maintain its structure without the metal (apo form) and bind it as a

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

(e.g. as part of

metal homeostasis Bioinorganic chemistry is a field that examines the role of metals in biology. Bioinorganic chemistry includes the study of both natural phenomena such as the behavior of metalloproteins as well as artificially introduced metals, including those t ...

). In other cases a coordinated metal cofactor is used in the

active site In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid residues that form temporary bonds with the substrate (binding site) a ...

of an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

to assist

catalysis Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

Histidine-rich metal-binding proteins

Poly-histidine tags (of six or more consecutive His residues) are utilized for protein purification by binding to columns with nickel or cobalt, with micromolar affinity. Natural poly-histidine peptides, found in the venom of the viper ''Atheris squamigera'' have been shown to bind Zn(2+), Ni(2+) and Cu(2+) and affect the function of venom metalloproteases. Furthermore, histidine-rich low-complexity regions are found in metal-binding and especially nickel-cobalt binding proteins. These histidine-rich low complexity regions have an average length of 36 residues, of which 53% histidine, 23% aspartate, 9% glutamate. Intriguingly, structured domains with metal binding properties also have very similar frequencies of these amino acids that are involved in the coordination of the metal.{{Cite journal, last=Dokmanić, first=Ivan, last2=Sikić, first2=Mile, last3=Tomić, first3=Sanja, date=March 2008, title=Metals in proteins: correlation between the metal-ion type, coordination number and the amino-acid residues involved in the coordination, url=https://pubmed.ncbi.nlm.nih.gov/18323620, journal=Acta Crystallographica. Section D, Biological Crystallography, volume=64, issue=Pt 3, pages=257–263, doi=10.1107/S090744490706595X, issn=0907-4449, pmid=18323620 Accordingly, it has been hypothesized that these metal-binding structured domains could have originated and evolved/optimized from metal-binding low-complexity protein regions of similar amino acid content.

References

Proteins