Biotic Stress/Applied Plant Bio


CS-8-6 - Functions and genetic interactions of chloroplast glutamyl endopeptidase (CGEP)

Sunday, July 15
4:58 PM - 5:00 PM


Chloroplast protein homeostasis is governed by a network of peptidases. Here we describe chloroplast glutamyl endopeptidase (CGEP), a new member of this proteostasis network. CGEP is a stromal peptidase and accumulates as a homo-oligomer in maize and Arabidopsis. CGEP is a member of S9D serine protease family with homologs in prokaryotes and photosynthetic eukaryotes, but not in archaea and non-photosynthetic eukaryotes. Phylogenetic analysis suggests that chloroplast CGEP originates from an early progenitor of plants and algae, and not from an endosymbiotic event as observed for many other chloroplast proteins. Recombinant rCGEP degrades peptides and smaller proteins, but not larger proteins. Arabidopsis rCGEP specifically cleaves substrates C-terminal of glutamate irrespective of neighboring residues, as shown using peptide libraries and a mass spectrometry-based PICS (Proteomic Identification of protease Cleavage Sites) method. In vitro and in vivo analysis demonstrates that CGEP undergoes C-terminal auto-cleavage at E945, removing last 15 residues. Lack of this C-terminal auto-cleavage lowers the upper size limit of substrates, i.e. it cannot digest the ~30 kDa β-CASEIN, while still efficiently degrading peptides and 10 kDa INSULIN. Homology models suggest that the C-terminal cleavage provides increased substrate access to the catalytic cavity. Arabidopsis null mutants (cgep) have no obvious visible phenotypes; however comparative proteomics does show effects on starch metabolism, specific changes in the stromal protein (un)folding machinery and an increase in ribosomal proteins. Furthermore, genetic interactions of CGEP with mutants in the stromal CLP protease (clpr2 and clpt1 clpt2), but not with several other chloroplast proteases (FTSH2 or PREP), were observed as reduced plant growth. Complementation of cgep x clp mutants with catalytically inactive CGEP-S781R or CGEP with an unprocessed C-terminus could not suppress these genetic interactions, demonstrating that CGEP peptidase activity and its autocatalytic cleavage are physiologically important.




Elden Rowland – Cornell University; Giulia Friso – Cornell University; Klaas van Wijk – Cornell University

Nazmul Bhuiyan

Research associate
Cornell University


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CS-8-6 - Functions and genetic interactions of chloroplast glutamyl endopeptidase (CGEP)

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