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.
Highlights
Proteins [1, 2]
We found that growth of the triple mutant was more sensitive than the wild type to high irradiances of visible light and that the PSII repair cycle was impaired [31]
That a dramatic growth defect was only observed in ⌬Deg argues against the possibility that the light-sensitive phenotype was due to polar effects on the expression of genes downstream of htrA, hhoA, and hhoB
Summary
Proteins [1, 2]. The photosystem two complex (PSII), which functions as the light-driven water:plastoquinone oxidoreductase in oxygenic photosynthetic electron transport, is prone to light-induced damage [3]. It remains unclear to what extent the Deg proteases are important for D1 degradation in vivo. This is a crucial question to address since recent biochemical experiments have suggested that a homologue of Deg in Synechocystis sp. The DegP/HtrA family of proteases was initially characterized in Escherichia coli and is composed of DegP ( known as HtrA), DegQ (or HhoA), and DegS (or HhoB) (reviewed in Ref. 14). They are serine-type proteases and are found in the periplasm (DegQ), attached to the periplasmic surface of the cytoplasmic membrane (DegP), or embedded in the cytoplasmic membrane facing the periplasm (DegS). Deg homologues in other bacteria show overlap in function [21, 22]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
