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Abstract

ClpP functions as the proteolytic subunit of the ATP-dependent Clp protease in eubacteria, mammals and plant chloroplasts. We have cloned a clpP gene, designated clpP1, from the cyanobacterium Synechococcus sp. PCC 7942. The monocistronic 591 bp gene codes for a protein 80% similar to one of four putative ClpP proteins in another cyanobacterium, Synechocystis sp. PCC 6803. The constitutive ClpP1 content in Synechococcus cultures was not inducible by high temperatures, but it did rise fivefold with increasing growth light from 50 to 175 micromol photons m(-2) s(-1). A clpP1 inactivation strain (delta clpP1) exhibited slower growth rates, especially at the higher irradiances, and changes in the proportion of the photosynthetic pigments, chlorophyll a and phycocyanin. Many mutant cells (ca. 35%) were also severely elongated, up to 20 times longer than the wild type. The stress phenotype of delta clpP1 when grown at high light was confirmed by the induction of known stress proteins, such as the heat shock protein GroEL and the alternate form of PSII reaction center D1 protein, D1 form 2. ClpP1 content also rose significantly during short-term photoinhibition, but its loss in delta clpP1 did not exacerbate the extent of inactivation of photosynthesis, nor affect the inducible D1 exchange mechanism, indicating ClpP1 is not directly involved in D1 protein turnover.

Distinctive Types of ATP-dependent Clp Proteases in Cyanobacteria

“…An additional role for ClpP1 other than within the soluble ClpP1/P2 proteolytic core is also consistent with the more severe phenotype exhibited by the ⌬clpP1 strain compared with ⌬clpP2 (21,26,36). Loss of ClpP1 significantly impairs the ability of Synechococcus to acclimate to adverse growth conditions including high light, low temperature and supplemental UV-B irradiation (26,36), whereas the ⌬clpP2 strain shows no such phenotype (21).…”

“…Arrows above the graph indicate molecular masses of protein standards used, and those below the graph indicate the peak location of the various complexes. the wild type under normal growth conditions, and they are the only two possible components of a Clp protease in Synechococcus that are non-essential for cell viability (21,26). Both proteins are also inducible by the same types of stress conditions including high light, cold, and supplemental UV-B irradiation (21,36).…”

“…Strains and Growth Conditions-Cultures of S. elongatus PCC 7942 wild type and the two mutant strains, ⌬clpP1 (26) and ⌬clpP2 (21), were grown in BG-11 inorganic medium (27) buffered with 10 mM 3-(N-morpholino) propanosulfonic acid (pH 7.5) and bubbled with 5% CO 2 in air at 37°C with continuous, white light of 70 mol of photons m Ϫ2 s Ϫ1 (28). Experimental cultures were inoculated from liquid precultures to a chlorophyll (Chl) concentration of 1.0 g ml Ϫ1 .…”

“…Besides those made in this study, polyclonal antibodies specific for Synechococcus ClpP1-3, ClpC, or ClpX have been described elsewhere (21,26,33). All primary antibodies were detected with a horseradish peroxidase-conjugated, anti-rabbit secondary antibody and visualized by enhanced chemiluminescence (ECL Plus, GE Healthcare).…”

Identification of a 350-kDa ClpP Protease Complex with 10 Different Clp Isoforms in Chloroplasts of Arabidopsis thaliana

“…The genome of the cyanobacterium Synechocystis PCC6803 has been completely sequenced and contains three ClpP genes and one ClpR gene (previously named ClpP4). In addition, three ClpP genes and one ClpR gene were also discovered in the cyanobacterium Synechococcus (44). In an attempt to understand if the ClpR genes in chloroplasts derived directly from the invading prokaryotic ancestor or from the ClpP genes after the endosymbiotic event, a second tree was built using the ClpP/R protein sequences from Arabidopsis, Synechocystis, and Synechococcus (Fig.…”