title: Molecular adaptation of the DegQ protease to exert protein quality control in the bacterial cell envelope.
abstract: To react to distinct stress situations and to prevent the accumulation of misfolded proteins, all cells employ a number of proteases and chaperones, which together set up an efficient protein quality control system. The functionality of proteins in the cell envelope of Escherichia coli is monitored by the HtrA proteases DegS, DegP, and DegQ. In contrast with DegP and DegS, the structure and function of DegQ has not been addressed in detail. Here, we show that substrate binding triggers the conversion of the resting DegQ hexamer into catalytically active 12- and 24-mers. Interestingly, substrate-induced oligomer reassembly and protease activation depends on the first PDZ domain but not on the second. Therefore, the regulatory mechanism originally identified in DegP should be a common feature of HtrA proteases, most of which encompass only a single PDZ domain. Using a DegQ mutant lacking the second PDZ domain, we determined the high resolution crystal structure of a dodecameric HtrA complex. The nearly identical domain orientation of protease and PDZ domains within 12- and 24-meric HtrA complexes reveals a conserved PDZ1 → L3 → LD/L1/L2 signaling cascade, in which loop L3 senses the repositioned PDZ1 domain of higher order, substrate-engaged particles and activates protease function. Furthermore, our in vitro and in vivo data imply a pH-related function of DegQ in the bacterial cell envelope.
authors.affiliation: Institute of Molecular Pathology, A-1030 Vienna, Austria.
authors.forename: Justyna
authors.initials: J
authors.lastname: Sawa
authors.affiliation: Department of Biological Sciences, Institute of Structural Molecular Biology, Birkbeck College, London WC1E 7HX, United Kingdom.
authors.forename: Hélène
authors.initials: H
authors.lastname: Malet
authors.affiliation: Institute of Molecular Pathology, A-1030 Vienna, Austria.
authors.forename: Tobias
authors.initials: T
authors.lastname: Krojer
authors.affiliation: Institute of Molecular Pathology, A-1030 Vienna, Austria.
authors.forename: Flavia
authors.initials: F
authors.lastname: Canellas
authors.affiliation: Centre for Medical Biotechnology, Faculty of Biology and Geography, University Duisburg-Essen, 45117 Essen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Ehrmann
authors.affiliation: Institute of Molecular Pathology, A-1030 Vienna, Austria. Electronic address: clausen@imp.univie.ac.at.
authors.forename: Tim
authors.initials: T
authors.lastname: Clausen
mesh_terms: D000495:Allosteric Site; D001426:Bacterial Proteins / Q000378:metabolism; D002151:Calorimetry / Q000379:methods; D002462:Cell Membrane / Q000378:metabolism*; D002850:Chromatography, Gel; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000502:physiology*; D006360:Heat-Shock Proteins / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008968:Molecular Conformation; D033903:Periplasmic Proteins / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012697:Serine Endopeptidases / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D057057:Serine Proteases / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; C066496:DegS protein, Bacteria; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D033903:Periplasmic Proteins; D057057:Serine Proteases; C061682:DegP protease; C098059:DegQ protein, E coli; D012697:Serine Endopeptidases