Carotenoids are produced by all photosynthetic organisms and a large number of bacteria and fungi. They are responsible for a lot of pigmentation in nature, as well as often playing an essential role in the provision of light protection to cells and as precursors of vitamin A in higher organisms. Myxobacton is the primary carotenoid ester generated in the photoresistant bacterium Myxococcus xanthus. It is created through a complex light-regulated gene expression cascade and acts to protect the bacteria from blue light and the resultant generation of damaging singlet oxygen species in the presence of porphyrins. The final stage in its production is a ketonisation, and the enzyme responsible for this stage was unknown in M. xanthus. We propose a possible location for the gene encoding such a ketolase, crtW. The gene is found located within a four-gene operon separate from the other known carotenoid biosynthetic genes, and appears to have two alternative promoter regions. The additional genes in the operon were found to encode a putative MutT/Nudix family hydrolase and a periplasmic, molybdopterin and haeme-dependent oxidoreductase, YedYZ. It is also shown that crtW transcription is independent of cell exposure to blue light and that the product is an inner membrane, integral membrane protein probable ketolase. The evolutionary origins of crtW are considered in conjunction with a number of other carotenoid biosynthetic enzymes, suggesting that the gene was one of the last to be acquired by M. xanthus.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:521380 |
| Date | January 2009 |
| Creators | Needham, James |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/3182/ |
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