Synthesising the pigments of life: Structure, function and regulation of metal chelatases in phototrophic bacteria

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Tetrapyrroles, the "pigments of life", are essential for respiration, photosynthesis, the nitrogen and sulphur cycles, and the biosynthesis of methane. The distinctive colours of tetrapyrroles, and their biochemical properties, depend on binding a metal ion such as magnesium in green chlorophylls or iron in hemes, which are red. Therefore, the enzymes that insert the metal ion into tetrapyrroles, called chelatases, are crucially important for most energy-yielding processes on Earth. For example, huge quantities of chlorophylls are synthesised and are essential for photosynthesis, which provides the biosphere with oxygen, food and energy, and heme is essential for respiratory electron transfer in bacteria, fungi, plants and mammals. We now need detailed structural information to gain a full understanding of how each class of chelatase inserts a specific metal, and how these complex enzymes are regulated in vivo.