CND41, a chloroplast DNA-binding protease, is involved in Rubisco degradation

Abstract

CND41 is a 41kDa DNA-binding protein with a basic pl isolated from chloroplast nucleoids of photomixotrophically cultured tobacco cells. CND41 has a transit peptide of 120 amino acids and a mature protein of 382 amino acids. The deduced amino acid sequence indicated that CND41 has active domain of aspartic protease. The purified CND41 had strong proteolytic activity at acidic pHs (pH2-4) (Murakami et al. FEBS Lett. 468:15(2000)). Furthermore, the fact that CND41 degraded denatured Rubisco at physiological pH suggests that it might be involved in Rubisco degradation. To confirm this idea in vivo, we examined the effect of nitrogen-depletion on the Rubisco degradation both in control (WT) and CND41 antisense (R22) tobacco. Analysis of total proteins and Rubisco clearly showed that those contents in WT deceased with leaf age, especially under nitrogen depletion condition, whereas those in R22 were rather constant through whole plant even under nitrogen-depletion. Western blot analysis also showed several bands of Rubisco-degradation products in young R22 leaves. These results indicated that CND41 plays an important role in the in vivo degradation of Rubisco both in young and senescent leaves.