Structural adaptation of the plant protease Deg1 to repair photosystem II during light exposure

Abstract

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.

Structural changes of the thylakoid membrane network induced by high light stress in plant chloroplasts

“…In particular, evidence exists that the activity of the STN8 kinase is dependent on the redox state of the plastoquinone pool [39,55]. Furthermore, the active forms of the FtsH and Deg proteases are hexamers [45,46,50]. For the Deg protease, it was found that oligomerization is triggered by acidic pH values in the thylakoid lumen [50].…”

“…Furthermore, the active forms of the FtsH and Deg proteases are hexamers [45,46,50]. For the Deg protease, it was found that oligomerization is triggered by acidic pH values in the thylakoid lumen [50]. As such, the structural rearrangements of thylakoid membranes should be seen as part of a complex regulatory network that controls the repair processes in thylakoid membranes.…”

“…Before D1 is inserted, the precursor D1 protein (pD1) is processed by CtpA (7). Finally, the PSII holocomplex reassembles and migrates back to stacked grana (8 [50,51]. For PBCP, STN8 and CtpA, the sizes were calculated from their relative molecular mass (RMM).…”

The modeled structures of Deg5 and Deg8 proteases in Arabidopsis thaliana

“…As mentioned in Section 1, the crystal structure of Deg1 contains a protease domain at the N-terminal and a PDZ domain at the C-terminal (see also Figure 2a) (Kley et al, 2011). When the structure of Deg5 was modeled using SWISS-MODEL with Deg1 as the template, we found that Deg5 was composed of 1 domain (residues 81-322) that encompassed 2 perpendicular β-barrel lobes with Nand C-terminal helices (helices H1 and H2) (Figure 2b).…”

AtDeg2 – a chloroplast protein with dual protease/chaperone activity

“…All of them possess a conservative AAA + domain which is responsible for ATP binding and hydrolysis, necessary to unfold protein substrates so that they can enter a catalytical chamber of the proteases molecule through a narrow entrance [1]. Nevertheless, some other proteases, including the Deg group, function in an ATP-independent manner, most probably because the availability of catalytic center is less restricted for unfolded substrates than in the case of ATP-dependent enzymes [2].…”