title: The Clp protease system is required for copper ion-dependent turnover of the PAA2/HMA8 copper transporter in chloroplasts.
abstract: The distribution of essential metal ions over subcellular compartments for use as cofactors requires control of membrane transporters. PAA2/HMA8 is a copper-transporting P1B -type ATPase in the thylakoid membrane, required for the maturation of plastocyanin. When copper is highly available to the plant this transporter is degraded, which implies the action of a protease. In order to identify the proteolytic machinery responsible for PAA2/HMA8 turnover in Arabidopsis, mutant lines defective in five different chloroplast protease systems were analyzed. Plants defective in the chloroplast caseinolytic protease (Clp) system were specifically impaired in PAA2/HMA8 protein turnover on media containing elevated copper concentrations. However, the abundance of a core Clp component was not directly affected by copper. Furthermore, the expression and activity of both cytosolic and chloroplast-localized superoxide dismutases (SODs), which are known to be dependent on copper, were not altered in the clp mutants, indicating that the loss of PAA2/HMA8 turnover in these lines was not caused by a lack of stromal copper. The results suggest that copper excess in the stroma triggers selection of the thylakoid-localized PAA2 transporter for degradation by the Clp protease, but not several other chloroplast proteases, and support a novel role for this proteolytic system in cellular copper homeostasis.
authors.affiliation: Biology Department, Colorado State University, Fort Collins, CO, 80523, USA.
authors.forename: Wiebke
authors.initials: W
authors.lastname: Tapken
authors.forename: Jitae
authors.initials: J
authors.lastname: Kim
authors.forename: Kenji
authors.initials: K
authors.lastname: Nishimura
authors.forename: Klaas J
authors.initials: KJ
authors.lastname: van Wijk
authors.forename: Marinus
authors.initials: M
authors.lastname: Pilon
mesh_terms: D000251:Adenosine Triphosphatases; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D027682:Cation Transport Proteins; D025222:Chloroplast Proton-Translocating ATPases / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D003300:Copper / Q000378:metabolism*; D000073840:Copper-Transporting ATPases; D049071:Endopeptidase Clp / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006706:Homeostasis; D026901:Membrane Transport Proteins / Q000378:metabolism; D009154:Mutation; D013482:Superoxide Dismutase / Q000378:metabolism; D020524:Thylakoids / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; D026901:Membrane Transport Proteins; D003300:Copper; D013482:Superoxide Dismutase; D049071:Endopeptidase Clp; D000251:Adenosine Triphosphatases; D025222:Chloroplast Proton-Translocating ATPases; C507153:PAA2 protein, Arabidopsis; D000073840:Copper-Transporting ATPases
keywords: P1B-type ATPase; caseinolytic protease (Clp); chloroplast; copper (Cu) homeostasis; copper transport; proteolysis; regulated protein turnover