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HtrA proteases have a conserved activation mechanism that can be triggered by distinct molecular cues

Abstract

HtrA proteases are tightly regulated proteolytic assemblies that are essential for maintaining protein homeostasis in extracytosolic compartments. Though HtrA proteases have been characterized in detail, their precise molecular mechanism for switching between different functional states is still unknown. To address this, we carried out biochemical and structural studies of DegP from Escherichia coli. We show that effector-peptide binding to the PDZ domain of DegP induces oligomer conversion from resting hexameric DegP6 into proteolytically active 12-mers and 24-mers (DegP12/24). Moreover, our data demonstrate that a specific protease loop (L3) functions as a conserved molecular switch of HtrA proteases. L3 senses the activation signal—that is, the repositioned PDZ domain of substrate-engaged DegP12/24 or the binding of allosteric effectors to regulatory HtrA proteases such as DegS—and transmits this information to the active site. Implications for protein quality control and regulation of oligomeric enzymes are discussed.

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Figure 1: DegP protease activation.
Figure 2: Crystal structures of DegP with the protease inhibitor DFP.
Figure 3: Peptide binding to DegP.
Figure 4: Peptide binding to PDZ1 triggers oligomer conversion.
Figure 5: Induced-fit binding to PDZ1.
Figure 6: The high-temperature crystal form of DegP.
Figure 7: Loop L3 senses the activation signal.
Figure 8: Molecular model for oligomer reassembly and protease activation of DegP.

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Acknowledgements

We thank I. Steinmacher and K. Mechtler for support with the MS analysis and C. Cowan for critical reading of the manuscript and helpful discussions. The Research Institute of Molecular Pathology is funded by Boehringer Ingelheim.

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T.K., R.H. and T.C. performed the X-ray studies, T.K. and J.S. performed biochemical studies, T.C. supervised the study and all authors discussed the results and approved the manuscript.

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Correspondence to Tim Clausen.

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The authors declare no competing financial interests.

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Krojer, T., Sawa, J., Huber, R. et al. HtrA proteases have a conserved activation mechanism that can be triggered by distinct molecular cues. Nat Struct Mol Biol 17, 844–852 (2010). https://doi.org/10.1038/nsmb.1840

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