title: The deg proteases protect Synechocystis sp. PCC 6803 during heat and light stresses but are not essential for removal of damaged D1 protein during the photosystem two repair cycle.
abstract: Members of the DegP/HtrA (or Deg) family of proteases are found widely in nature and play an important role in the proteolysis of misfolded and damaged proteins. As yet, their physiological role in oxygenic photosynthetic organisms is unclear, although it has been widely speculated that they participate in the degradation of the photodamaged D1 subunit in the photosystem two complex (PSII) repair cycle, which is needed to maintain PSII activity in both cyanobacteria and chloroplasts. We have examined the role of the three Deg proteases found in the cyanobacterium Synechocystis sp. PCC 6803 through analysis of double and triple insertion mutants. We have discovered that these proteases show overlap in function and are involved in a number of key physiological responses ranging from protection against light and heat stresses to phototaxis. In previous work, we concluded that the Deg proteases played either a direct or an indirect role in PSII repair in a glucose-tolerant version of Synechocystis 6803 (Silva, P., Choi, Y. J., Hassan, H. A., and Nixon, P. J. (2002) Philos. Trans. R. Soc. Lond. B Biol. Sci. 357, 1461-1467). In this work, we have now been able to demonstrate unambiguously, using a triple deg mutant created in the wild type strain of Synechocystis 6803, that the Deg proteases are not obligatory for PSII repair and D1 degradation. We therefore conclude that although the Deg proteases are needed for photoprotection of Synechocystis sp. PCC 6803, they do not play an essential role in D1 turnover and PSII repair in vivo.
authors.affiliation: Divisions of Biology and Molecular Biosciences, Faculty of Natural Sciences, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom.
authors.forename: Myles
authors.initials: M
authors.lastname: Barker
authors.forename: Remco
authors.initials: R
authors.lastname: de Vries
authors.forename: Jon
authors.initials: J
authors.lastname: Nield
authors.forename: Josef
authors.initials: J
authors.lastname: Komenda
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Nixon
mesh_terms: D005947:Glucose / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006358:Hot Temperature; D008027:Light; D008854:Microscopy, Electron; D008957:Models, Genetic; D009154:Mutation; D010100:Oxygen / Q000378:metabolism; D033903:Periplasmic Proteins / Q000378:metabolism*; D017785:Photons; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000378:metabolism*; D046939:Synechocystis / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors
chemical_list: D006360:Heat-Shock Proteins; D033903:Periplasmic Proteins; D045332:Photosystem II Protein Complex; C061682:DegP protease; D012697:Serine Endopeptidases; D005947:Glucose; D010100:Oxygen