title: Recombinant Deg/HtrA proteases from Synechocystis sp. PCC 6803 differ in substrate specificity, biochemical characteristics and mechanism.
abstract: 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.
authors.affiliation: Department of Biology, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany.
authors.forename: Pitter F
authors.initials: PF
authors.lastname: Huesgen
authors.forename: Helder
authors.initials: H
authors.lastname: Miranda
authors.forename: XuanTam
authors.initials: X
authors.lastname: Lam
authors.forename: Manuela
authors.initials: M
authors.lastname: Perthold
authors.forename: Holger
authors.initials: H
authors.lastname: Schuhmann
authors.forename: Iwona
authors.initials: I
authors.lastname: Adamska
authors.forename: Christiane
authors.initials: C
authors.lastname: Funk
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000378:metabolism; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity; D046939:Synechocystis / Q000378:metabolism*; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D012697:Serine Endopeptidases; D008274:Magnesium; D002118:Calcium