Determination of a Chloroplast Degron in the Regulatory Domain of Chlorophyllide a Oxygenase

Chlorophyll b is one of the major photosynthetic pigments of plants. The regulation of chlorophyll b biosynthesis is important for plants in order to acclimate to changing environmental conditions. In the chloroplast, chlorophyll b is synthesized from chlorophyll a by chlorophyllide a oxygenase (CAO...

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Bibliographic Details
Published in:The Journal of biological chemistry 2009-12, Vol.284 (52), p.36689-36699
Main Authors: Sakuraba, Yasuhito, Tanaka, Ryouichi, Yamasato, Akihiro, Tanaka, Ayumi
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Arabidopsis - enzymology
Arabidopsis - genetics
Arabidopsis Proteins - genetics
Arabidopsis Proteins - metabolism
Chlorophyll - genetics
Chlorophyll - metabolism
Chlorophyll A
Chloroplasts - enzymology
Chloroplasts - genetics
Endopeptidase Clp - genetics
Endopeptidase Clp - metabolism
Enzyme Stability - physiology
Oxygenases - genetics
Oxygenases - metabolism
Protein Structure, Tertiary - physiology
Protein Synthesis, Post-Translational Modification, and Degradation
Sequence Deletion
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Summary:Chlorophyll b is one of the major photosynthetic pigments of plants. The regulation of chlorophyll b biosynthesis is important for plants in order to acclimate to changing environmental conditions. In the chloroplast, chlorophyll b is synthesized from chlorophyll a by chlorophyllide a oxygenase (CAO), a Rieske-type monooxygenase. The activity of this enzyme is regulated at the level of protein stability via a feedback mechanism through chlorophyll b. The Clp protease and the N-terminal domain (designated the A domain) of CAO are essential for the regulatory mechanism. In this study, we aimed to identify the specific amino acid residue or the sequence within the A domain that is essential for this regulation. To accomplish this goal, we randomly introduced base substitutions into the A domain and searched for potentially important residues by analyzing 1,000 transformants of Arabidopsis thaliana. However, none of the single amino acid substitutions significantly stabilized CAO. Therefore, we generated serial deletions in the A domain and expressed these deletions in the background of CAO-deficient Arabidopsis mutant. We found that the amino acid sequence 97QDLLTIMILH106 is essential for the regulation of the protein stability. We furthermore determined that this sequence induces the destabilization of green fluorescent protein. These results suggest that this sequence serves as a degradation signal that is recognized by proteases functioning in the chloroplast.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M109.008144