20S proteasome prevents oxidized proteins accumulation in maize leaf segments under low cadmium levels

LB PENA; CE AZPILICUETA; MS ZAWOZNIK; SM GALLEGO

Buenos Aires

Workshop; Workshop. Oxidative stress and antioxidants; 2009

Facultad de Farmacia y Bioquímica, UBA

In order to examine the possible involvement of the 20S proteasome in degradation of oxidized proteins, the effects of different cadmium concentrations on its activities, protein abundance and oxidation level were studied using maize (Zea mays L.) leaf segments. The accumulation of carbonylated and ubiquitinated proteins was also investigated. Treatment with 50 µM CdCl2 increased both trypsinand PGPH-like activities of the 20S proteasome. The incremental changes in 20S proteasome activities were probably caused by an increased level of 20S proteasome oxidation, with this being responsible for degradation of the oxidized proteins. When leaf segments were treated with 100 µM CdCl2, the chymotrysin- and trypsin-like activities of the 20S proteasome also decreased, with a concomitant increase in accumulation of carbonylated and ubiquitinated proteins. With both Cd2+ concentrations, the abundance of the 20S proteasome protein remained similar to the control experiments. In conclusion, under low cadmium treatment, the increase in the 20S proteasome activity due to its moderate oxidation was responsible for preventing oxidized proteins accumulation, however, higher cadmium concentration decreased 20S proteasome activity with a concomitant accumulation of oxidized and ubiquitinated proteins. These results provide evidence for the involvement of this proteolytic system in cadmium-stressed plants.