CLPS: A NOVEL SUBSTRATE SELECTOR OF THE CLP SYSTEM IN Arabidopsis thaliana

COLOMBO, CLARA V.; ROSANO, GERMÁN L.; MOGK, AXEL; CECCARELLI, EDUARDO A.

Buenos Aires

Congreso; Argentine Society for Biochemistry and Molecular Biology scientific meeting 2013; 2013

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Proteolysis is an essential mechanism in protein quality control. In chloroplasts, this function is accomplished by the ClpPR complex, which acts as a protein-degradation machine. The chaperones ClpC1/ 2 and ClpD select and unfold substrate proteins and translocate them to ClpPR. However, target selection appears to be aided by adaptor proteins that bind to the chaperones. For example, ClpS is proposed to modulate ClpC1/2 substrate selection and affinity, yet its function is unknown. Interestingly, ClpS from Escherichia coli is the discriminator of the N-end rule pathway. The rule states that the half-life of a protein is determined by the nature of its aminoterminal residue. E. coliClpS recognizes N-end rule substrates and presents them to the ClpAP protease. Based on these observations from bacteria and the fact that ClpS is present in plants, the existence of the N-end rule pathway in chloroplast is possible. Using recombinant ClpS from Arabidopsis thaliana, we found by gel filtration chromatography that it can form homo-oligomers of 2, 3, 4 and 6 subunits. ClpS was found to interact with ClpC2 and ClpD, which is in line with its proposed biological function. Importantly, ClpS was able to bind substrates recognized by E. coliClpS. Our results suggest that ClpS plays a role in substrate selection for the Clp system in plants, maybe following the rules of the N-end pathway.