metallochaperones

metallochaperones [mə‚tal·ō′shap·ə‚rōnz]

(biochemistry)

Metalloproteins that aid in the insertion of the appropriate metal ion into a metalloenzyme.

A family of proteins that shuttles metal ions to specific intracellular locations where metalloenzymes bind to the metal ions and use them as cofactors to carry out essential biochemical reactions.

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Metallochaperones

A family of proteins that shuttle metal ions to specific sites within a cell. The target sites for metal delivery include a number of metalloenzymes, or proteins that bind metal ions, such as copper, zinc, or iron, and use these ions as cofactors to carry out essential biochemical reactions. Metallochaperones escort the ion to a specific intracellular location and facilitate incorporation of the metal into designated metalloenzymes. See Cell (biology)

The bulk of current knowledge on metallochaperones is restricted to copper, although it is reasonable to assume that a distinct class of proteins is responsible for the incorporation of other metal ion cofactors into metalloenzymes. Among the metallochaperones that have been studied in detail are a family of three copper chaperones. These molecules operate in eukaryotic (nucleated) cells to direct copper to distinct intracellular locations: the mitochondria, the secretory pathway, and the cytosol.

Intracellular copper is normally present at exquisitely low levels, and activation of copper enzymes is wholly dependent upon copper chaperones. Copper not only is an essential nutrient but also is quite toxic to living cells, and elaborate detoxification mechanisms prevent the free metal ion from accumulating to any substantial degree. The copper-requiring metalloenzymes cannot compete for these vanishingly low levels of available metal, explaining the requirement for the copper metallochaperones.