Genetic basis of microbial carotenogenesis |
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Authors: | C?Sieiro M?Poza T?de?Miguel Email author" target="_blank">T?G?VillaEmail author |
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Institution: | (1) Departamento de Microbiología y Parasitología, Facultad de Farmacia, Universidad de Santiago de Compostela, 15782, Santiago de Compostela, Spain, |
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Abstract: | The synthesis of carotenoids begins with the formation of a phytoene from geranylgeranyl pyrophosphate, a well conserved
step in all carotenogenic organisms and catalyzed by a phytoene synthase, an enzyme encoded by the crtB (spy) genes. The next step is the dehydrogenation of the phytoene, which is carried out by phytoene dehydrogenase. In organisms
with oxygenic photosynthesis, this enzyme, which accomplishes two dehydrogenations, is encoded by the crtP genes. In organisms that lack oxygenic photosynthesis, dehydrogenation is carried out by an enzyme completely unrelated to
the former one, which carries out four dehydrogenations and is encoded by the crtI genes. In organisms with oxygenic photosynthesis, dehydrogenation of the phytoene is accomplished by a ζ-carotene dehydrogenase
encoded by the crtQ (zds) genes. In many carotenogenic organisms, the process is completed with the cyclization of lycopene. In organisms exhibiting
oxygenic photosynthesis, this step is performed by a lycopene cyclase encoded by the crtL genes. In contrast, anoxygenic photosynthetic and non-photosynthetic organisms use a different lycopene cyclase, encoded
by the crtY (lyc) genes. A third and unrelated type of lycopene β-cyclase has been described in certain bacteria and archaea. Fungi differ
from the rest of non-photosynthetic organisms in that they have a bifunctional enzyme that displays both phytoene synthase
and lycopene cyclase activity. Carotenoids can be modified by oxygen-containing functional groups, thus originating xanthophylls.
Only two enzymes are necessary for the conversion of β-carotene into astaxanthin, using several ketocarotenoids as intermediates,
in both prokaryotes and eukaryotes. These enzymes are a β-carotene hydroxylase (crtZ genes) and a β-carotene ketolase, encoded by the crtW (bacteria) or bkt (algae) genes.
Electronic Publication |
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Keywords: | Carotenes Xanthophylls Biosynthesis Genetics |
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