Zach Adam - Deg proteases in the thylakoid lumen - are they 'more of the same'?

January 2017

  • Datum: 11.01.2017
  • Uhrzeit: 14:00 - 15:30
  • Vortragende(r): Zach Adam
  • The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University, Rehovot, Israel
  • Ort: Central Building
  • Raum: Seminar Room
  • Gastgeber: Salma Balazadeh
Prokaryotic Deg (HtrA) proteases are involved in protein quality control and response to stress [1]. The Arabidopsis thaliana genome contains 16 Deg genes whose products are distributed in chloroplasts, mitochondria, peroxisomes and the nucleus [2]. Deg2 and Deg7 are located in the chloroplast stroma, whereas Deg1, Deg5 and Deg8 are found in the thylakoid lumen. Deg1 forms active homo-hexamers at acidic pH, degrading photosynthetic proteins, especially in relation to the PSII repair cycle [3,4]. Deg5 and Deg8 form hetero-complexes, performing apparently similar functions [5], raising the question whether the two complexes are redundant. To answer this, we generated a full set of single, double and triple KO mutants and compared their phenotypes. We found that under optimal growth conditions Deg5-Deg8 mutants look like WT, but Deg1 mutants are smaller and show higher sensitivity to photoinhibition. Under harsher conditions, Deg5-Deg8 mutants are also affected, although less than Deg1 mutants. However, the functions of the two complexes are somewhat redundant, as overexpression of Deg5-Deg8 can partially compensate for the loss of Deg1. Comparative proteomics revealed in the triple mutant moderate up-regulation of thylakoid proteins involved in folding, translocation, assembly and degradation, and down-regulation of components of all photosynthetic complexes. Testing the steady-state level of the thylakoid Deg proteases in WT plants demonstrated that Deg1 is approximately two-fold more abundant than the Deg5-Deg8 complex. Moreover, recombinant Deg1 had higher in vitro proteolytic activity compared with Deg5, Deg8 and the combination of the two. These results suggest that the differences in abundance and proteolytic activity are the source of the differential importance of the two complexes in vivo.

[1] Clausen, T. et al. (2011) HTRA proteases: regulated proteolysis in protein quality control. Nat Rev Mol Cell Biol. 12: 152-162.

[2] Schuhmann, H. and I. Adamska. (2012) Deg proteases and their role in protein quality control and processing in different subcellular compartments of the plant cell. Physiol Plant. 145: 224-234.

[3] Kapri-Pardes, E. et al. (2007) The thylakoid lumen protease Deg1 is involved in the repair of photosystem II from photoinhibition in Arabidopsis. Plant Cell. 19: 1039-1047.

[4] Kley, J. et al. (2011) Structural adaptation of the plant protease Deg1 to repair photosystem II during light exposure. Nat Struct Mol Biol. 18 728-731.

[5] Sun, X. et al. (2007) Formation of DEG5 and DEG8 complexes and their involvement in the degradation of photodamaged photosystem II reaction center D1 protein in Arabidopsis. Plant Cell. 19: 1347-1361.

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