Deg1 is a chloroplastic protease involved in maintaining the photosynthetic machinery. Structural and biochemical analyses reveal that the inactive Deg1 monomer is transformed into the proteolytically active hexamer at acidic pH. The change in pH is sensed by His244, which upon protonation, repositions a specific helix to trigger oligomerization. This system ensures selective activation of Deg1 during daylight, when acidification of the thylakoid lumen occurs and photosynthetic proteins are damaged.
Bibliographical noteFunding Information:
We thank R. Huber Max Planck Institute for Biochemistry and J.M. Peters Research Institute of Molecular Pathology for critical reading of the manuscript and helpful discussion, D. Charuvi (Hebrew University) for calculating the volume of the thylakoid lumen and C. Wilken Research Institute of Molecular Pathology for help with crystallizing Deg1. Crystallographic experiments were conducted at the beamline ID14-EH4 at the European Synchrotron Radiation Facility. This research was supported in part by a grant from the Israel Science Foundation to Z.A. The Research Institute of Molecular Pathology (IMP) is funded by Boehringer Ingelheim.