A CK2 site is reversibly phosphorylated in the photosystem II subunit CP29

Abstract

Protein phosphorylation is a major mechanism in the regulation of protein function. In chloroplast thylakoids several photosystem II subunits, including the major antenna lightharvesting 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 conformationai 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 phosphorylation site on the N-terminal, stromaexposed domain, showing that it is located in a sequence not homologous to the other members of the Lhc family. The phosphorylated 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 transdnction pathway is discussed. 1, IntroductionIn the chloroplast, phosphorylation of membrane proteins i. responsible for many of the physiological responses to hanges in incident light and redox poise. The major substrate iavolved in this regulative process is the light-harvesting comllex of photosystem II (LHCII). When PSII is overexcited with respect to PSI, the plastoquinone pool becomes reduced i,nd thus activates a kinase bound to the cytochrome b6/f t omplex [l,2]. This process results in phosphorylation of the Jaajor trimeric LHCII complex in an N-terminal, stroma-exl,osed site [3] leading to the monomerisation of LHCII, dis-, onnection from PSII RC [2,4] and migration of LHCII ~aonomeric subpopulations from grana to stroma membranes t 2,5,6] where they can transfer excitation energy to PSI [5] and bus oxidise the plastoquinone pool. This process can there~ore be understood in terms of regulation of photosystem ntenna size by the transfer of LHCII units away from the Corresponding author. Fax: (39) 45-8098929. ~-mail: bassi@biotech.univr.it tbbreviations. BBY, PSII membrane preparation; CK2, casein kinase !; Chl, chlorophyll; CP, chlorophyll-protein; DM, dodecyl-maltoside; EDTA, ethylenediaminetetraacetic acid; ELFE, electroendoosmotic ~'lectrophoresis; HEPES, N-2-(hydroxy-ethyl)piperazine-N'-2-ethane~ulfonic acid; IEF, isoelectrofocusing; LHCII, light-harvesting complex of PSII; PAGE, polyacrylamide gel electrophoresis; PS, photosystem; rCP29, recombinant CP29 reconstituted from the apoprotein derivatives overproduced in bacteria; RC, reaction centre; ~;DS, sodium dodecyl sulphate; Tris, 2-amino-2-(hydroxymethyl)-l,3-l~ropanediol overexcited photosystem [2]. The underlying mechanism is a conformational change of the LHCII N-terminal portion which undocks this subunit from PSII and increases its affinity for PSI [2].More recently, it was reported that photoinhibitory conditions induce reversible phosphorylation of CP29, another PSII subunit PSI [7]. Although there is strong homology between CP29 and LHCII and both protei...

A novel plant protein undergoing light-induced phosphorylation and release from the photosynthetic thylakoid membranes

“…Most thylakoid phosphoproteins are singly phosphorylated, and only the 9-kDa PsbH gene product has two phosphorylation sites (12,43). The previously characterized thylakoid phosphoproteins constitute the major photosynthetic protein complexes (12,13,(20)(21)(22), and the phosphorylation sites in analogous proteins from different plants are rather conserved (19). Comparison of the protein sequences deduced from ESTs of 20 different plants with spinach TSP9 does not show a high conservation for the phosphorylated threonine residues.…”

“…Additional modulation of protein phosphorylation in thylakoid membranes involves the thiol redox state (8,9) as well as light-modulated conformational changes of substrate proteins (10). Activated thylakoid kinases phosphorylate the membrane proteins of photosystem II (PSII) and its light-harvesting antenna (LHCII) as well as a number of still unidentified protein substrates (2,(11)(12)(13). The protein dephosphorylation reactions are catalyzed by both integral thylakoid membrane and soluble chloroplast phosphatases (2,14).…”

Protein Tyrosine Kinases and Protein Tyrosine Phosphatases Are Involved in Abscisic Acid-Dependent Processes in Arabidopsis Seeds and Suspension Cells

“…5C, spot K; Table I). According to the BLASTP analysis, this protein is related to the RNA-binding protein GRPA from maize encoded by a gene whose expression is induced by ABA and that can be phosphorylated (Gomez et al, 1988;Testi et al, 1996). Many genetic approaches have led to the identification of RNA-binding proteins that act in ABA signaling during germination and drought tolerance (Kuhn and Schroeder, 2003).…”

Arabidopsis Mutants Deleted in the Light-Harvesting Protein Lhcb4 Have a Disrupted Photosystem II Macrostructure and Are Defective in Photoprotection

“…Indeed, the maintenance of Lhcb4, in HL stress conditions that leads to the reduction of Lhcb6 and LHCII (Ballottari et al, 2007), suggests that Lhcb4 might be a key factor in light harvesting and photoprotection. Lhcb4 phosphorylation in both monocots (Testi et al, 1996) and dicots (Hansson and Vener, 2003;Tikkanen et al, 2006) affects the spectral properties of the protein and correlates with higher resistance to HL and cold (Bergantino et al, 1995;Mauro et al, 1997) and water stress (Liu et al, 2009). Although the mechanism of this protective effect is unknown, there is evidence for a link between Lhcb4 and NPQ, since the protein has been identified as an interaction partner of PsbS (Teardo et al, 2007), the pH-dependent trigger of qE (Li et al, 2000), and it is part of a pentameric complex whose dissociation is indispensable for the establishment of NPQ (Betterle et al, 2009).…”