Abstract
Photosynthetic energy metabolism is a dynamic process in which the activity and/or abundance of photosynthetic components should be properly regulated to adapt to various environments. However, molecular processes underlying this regulation have remained largely uncharacterized. 2-DE and immunoblot analyses using wild watermelon revealed the presence of two isoforms for ε subunit of chloroplast ATP synthase, which had similar molecular weights but showed different isoelectric points. To identify the structural difference of the two ε proteins, we purified them and subjected to mass spectrometry. Consequently, the difference was found to be the presence/absence of N-terminal acetylation. Interestingly, the stress resulted in the preferential decrease in the abundance of the ε subunit without N-terminal acetylation. Moreover, we detected a metalloprotease activity which catalyzed preferential degradation of ε protein. These observations suggested that the acetylation of ε subunit at its N-terminus confers resistance to the metalloprotease, thereby involving in the quantitative regulation of the ε subunit in vivo.
