Thylakoid protein phosphorylation

Gal A, Zer H and Ohad I (1997) Redox-controlled thylakoid protein phosphorylation. News and views. Physiol Plant 100 869-885... 

LHCII and several PSII thylakoid proteins are phosphorylated by an ATP dependent protein kinase (1,2), which is under control of the redox state of the PQ pool (3). This protein phosphorylation leads to rearrangements in the lateral organization of the thylakoid membrane... 

In general, ATP is used as phosphate donor in phosphorylation reactions of thylakoid proteins. This report for the first time will demonstrate that also inorganic pyrophosphate (PPi) can be used as phosphate donor for thylakoid protein phosphorylation. 

Protein phosphorylation was carried out by a standard method as described in (7) with the exception that (32p)ppi was used as phosphate donor instead of (y- P)ATP. Isolated thylakoids were phosphorylated by illumination (500 pE m"2 s l) in the presence of 0.4 mM (32p)ppi (300 000 cpm/nmol PPi). Phosphorylation was terminated by adding 10% cold TCA. Thylakoids were washed, solubilized in SDS at 70 C, and fractionated by SDS-PAGE using a 12-22.5% acrylamide gradient (8). The thylakoid proteins were detected by staining the gel with Coomassie brilliant blue and radioactivity was located by autoradiography. 

NH4C1 and added ATP on PPi dependent light induced thylakoid protein phosphorylation. Experimental conditions were the same as in Methods. Thylakoids were illuminated for 10 min. A - no additions ... 

To date, three candidate thylakoid protein kinases have been isolated, of 23 kDa and 38 kDa [5,6] and of 64 kDa [7]. Of these only the 64 kDa protein was able to phosphorylate exogenous LHCII. 

The thylakoid protein kinase is a 64kDa polypeptide capable of autophosphorylation on a serine residue and of phosphorylating... 

Phosphorylation of spinach thylakoid proteins was performed at 0 C. Stroma thylakoid vesicles were isolated directly after the phosphorylation was terminated or after incubation of the sample at a higher temperature for a certain time period. 

THYLAKOID PROTEIN PHOSPHORYLATION IN AN ALGAE WITH CHLOROPHYLL A/C/FUCOXANTHIN LIGHT HARVESTING ANTENNA. 

A small decrease in Fv/Fm was observed after LL-chill treatment, however this was attributable to an increase in Fo, not a decrease in Fm. Interestingly LL-chill treatment produced no effect on either the light-limited or saturated rates of PS2 electron transport associated with photoinhibition of PS2. Phosphorylation of thylakoid proteins produced the expected decrease in Fv/Fm for control membranes, but had little effect on Fv/Fm of both HL-chill and LL-chill thylakoids (Table 1), This was surprising since LHC2 was heavily phosphorylated in both HL-chill and LL-chill thylakoids (Fig. 1), Clearly LHC2 phosphorylation is not ubiquitously associated with a decrease in Fv/Fm. 

Regulation of Photosynthetis a- to p-Conversion of Photosystem II and Thylakoid Protein Phosphorylation 771... 

Thylakoid Protein Phosphorylation in an Algae with Chlorophyll A/C/Fucoxanthin Light... 

Chill-Induced Modifications to the Relationship Between Thylakoid Protein Phosphorylation and Energy Distribution ot Photosystem 2 in Maize 679... 

Horton P (1983) Control of chloroplast electron transport by phosphorylation of thylakoid proteins, FEBS Lett. 152, 47-52. 

PS II absorbs more light than PS I. As such PS I cannot take electrons as fast as PS II can supply, leaving plastoquinone in its reduced state. This reduced plastoquinone activates a protein kinase that phosphorylates the threonine (Thr) residue of the LHCs that in turn migrate to the unstacked portion of the thylakoid membrane where it binds to PS I. As a result, a large portion of incident light is funneled to PS I. 

An important step towards the understanding of the regulation of excitation energy partition between the two photosystems has been the discovery of LHC phosphorylation by a thylakoid-bound protein kinase and its dephosphorylation by a phosphatase [124]. The kinase is activated when the plastoquinone pool is reduced, and inactivated when it becomes oxidized [125,126]. Phosphorylation of LHC leads to a decrease of PS II fluorescence of ca. 15-20%, and dephosphorylation to the opposite changes [127-129]. PS I photochemical activity is at the same time enhanced [130-133],... 

It has been demonstrated that phosphorylation of LHC causes the detachment of a fraction of it from PS II and its lateral migration in the membrane to become incorporated into PS I [134-136]. It has indeed been shown that the fluorescence quenching caused by LHC phosphorylation is qualitatively different from spillover, because only LHC is quenched, not PS II [136], and Fq as well as are quenched [136,137]. The phosphorylation of LHC and/or of other thylakoid polypeptides may have more complex effects, and their interactions are far from being understood. It has been reported that protein phosphorylation enhances PS I-de-pendent cyclic photophosphorylation even under light saturation conditions [133], which could not be explained merely on the basis of PS I antenna enlargement. 

The two protons from plastoquinol are released into the thylakoid lumen. This reaction is reminiscent of that catalyzed by ubiquinol cytochrome c oxidoreductase in oxidative phosphorylation. Indeed, most components of the enzyme complex that catalyzes the reaction, the cytochrome bf complex, are homologous to those of ubiquinol cytochrome c oxidoreductase. The cytochrome hf complex includes four subunits a 23-kd cytochrome with two Z>-type hemes, a 20-kd Rieske-type Fe-S protein, a 33-kd cytochrome/with a c-type cytochrome, and a 17-kd chain. 

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