Protein phosphorylation is a major mechanism in the regulation of protein function. In chloroplast thylakoids several photosystem II subunits, including the major antenna light-harvesting complex II and several core complex components, are reversibly phosphorylated depending on the redox state of the electron carriers. A previously unknown reversible phosphorylation event has recently been described on the CP29 subunit which leads to conformational changes and protection from cold stress (Bergantino, E., Dainese, P., Cerovic, Z., Sechi, S. and Bassi, R. (1995) J. Biol. Chem. 270, 8474-8481). In this study, we have identified the phosphory]ation site on the N-terminal, stroma-exposed domain, showing that it is located in a sequence not homologous to the other members of the Lhc family. The phosphory]ated sequence is unique in chloroplast membranes since it meets the requirements for CK2 (casein kinase II) kinases. The possibility that this phosphorylation is involved in a signal transduction pathway is discussed.
- Cold stress
- Light-harvesting complex