Recombinant Deg/HtrA proteases from Synechocystis sp. PCC 6803 differ in substrate specificity, biochemical characteristics and mechanism

Cyanobacteria require efficient protein-quality-control mechanisms to survive under dynamic, often stressful, environmental conditions. It was reported that three serine proteases, HtrA (high temperature requirement A), HhoA (HtrA homologue A) and HhoB (HtrA homologue B), are important for survival of Synechocystis sp. PCC 6803 under high light and temperature stresses and might have redundant physiological functions. In the present paper, we show that all three proteases can degrade unfolded model substrates, but differ with respect to cleavage sites, temperature and pH optima. For recombinant HhoA, and to a lesser extent for HtrA, we observed an interesting shift in the pH optimum from slightly acidic to alkaline in the presence of Mg2+ and Ca2+ ions. All three proteases formed different homo-oligomeric complexes with and without substrate, implying mechanistic differences in comparison with each other and with the well-studied Escherichia coli orthologues DegP (degradation of periplasmic proteins P) and DegS. Deletion of the PDZ domain decreased, but did not abolish, the proteolytic activity of all three proteases, and prevented substrate-induced formation of complexes higher than trimers by HtrA and HhoA. In summary, biochemical characterization of HtrA, HhoA and HhoB lays the foundation for a better understanding of their overlapping, but not completely redundant, stress-resistance functions in Synechocystis sp. PCC 6803

Biochemical and physiological characterisation of Deg/HtrA proteases in Synechocystis sp. PCC 6803

Deg/HtrA proteases are ATP-independent endoproteases that can be found in almost every organism and possess, besides a protease domain with a catalytically active serine residue, up to four PDZ domains, which mediate i.a. copmlex formation. The three Deg/HtrA proteases HhoA, HtrA and HhoB in Synechocystis sp. PCC 6803 are of special interest, because they combine features of their plant and bacterial homologues and are thought to be involved in responses to abiotic stresses and turnover of the PSII reaction centre protein D1. This study focused on the role of the cyanobacterial Deg/HtrA proteases in the short-term response to elevated salt concentrations, particularly on changes in levels of photosynthesis-related proteins and florescence kinetics. Furthermore, state-of-the-art methods for substrate identification were tested for their practicability in cyanobacteria and the role of the PDZ domain in the oligomerisation process was determined

Materialoberfläche wichtig für Qualität und Stahl

Am Institut für Werkstoffsystemtechnik (WITG) wurden die Einflussfaktoren der Bearbeitung auf die Oberflächeneigenschaften sowie die daraus resultierende Korrosionsbeständigkeit bei nichtrostenden Stählen für die Produktion von pharmazeutischen Produkten untersucht