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Identification of new protein substrates for the chloroplast ATP-dependent Clp protease supports its constitutive role in Arabidopsis.

Artikel i vetenskaplig tidskrift
Författare Tara M Stanne
Lars Sjögren
Shai Koussevitzky
Adrian K Clarke
Publicerad i The Biochemical journal
Volym 417
Nummer/häfte 1
Sidor 257-68
ISSN 1470-8728
Publiceringsår 2009
Publicerad vid Institutionen för växt- och miljövetenskaper
Sidor 257-68
Språk en
Länkar dx.doi.org/10.1042/BJ20081146
Ämnesord Adenosine Triphosphate, metabolism, Arabidopsis, enzymology, genetics, metabolism, Arabidopsis Proteins, genetics, metabolism, Chlorophyll, metabolism, Chloroplasts, enzymology, genetics, metabolism, Electrophoresis, Gel, Two-Dimensional, Endopeptidase Clp, genetics, metabolism, Gene Expression Regulation, Plant, Heat-Shock Proteins, genetics, metabolism, Photosynthesis, genetics, physiology, Plant Leaves, enzymology, genetics, metabolism, Plants, Genetically Modified, enzymology, genetics, metabolism
Ämneskategorier Biologiska vetenskaper

Sammanfattning

The ATP-dependent Clp protease in plant chloroplasts consists of a heterogeneous proteolytic core containing multiple ClpP and ClpR paralogues. In this study, we have examined in detail the only viable knockout mutant to date of one of these subunits in Arabidopsis thaliana, ClpR1. Loss of ClpR1 caused a slow-growth phenotype, with chlorotic leaves during early development that later partially recovered upon maturity. Analysis of the Clp proteolytic core in the clpR1 mutant (clpR1-1) revealed approx. 10% of the wild-type levels remaining, probably due to a relative increase in the closely related ClpR3 protein and its partial substitution of ClpR1 in the core complex. A proteomic approach using an in organello proteolytic assay revealed 19 new potential substrates for the chloroplast Clp protease. Many of these substrates were constitutive enzymes involved in different metabolic pathways, including photosynthetic carbon fixation, nitrogen metabolism and chlorophyll/haem biosynthesis, whereas others function in housekeeping roles such as RNA maturation, protein synthesis and maturation, and recycling processes. In contrast, degradation of the stress-related chloroplast proteins Hsp21 (heat-shock protein 21) and lipoxygenase 2 was unaffected in the clpR1-1 line and thus not facilitated by the Clp protease. Overall, we show that the chloroplast Clp protease is principally a constitutive enzyme that degrades numerous stromal proteins, a feature that almost certainly underlies its vital importance for chloroplast function and plant viability.

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