Immunological evidence for apoproteins of the light-harvesting chlorophyll-protein complex in a mutant of barley lacking chlorophyll b

Light-harvesting chlorophyll a/b-protein: Three-dimensional structure of a reconstituted membrane lattice in negative stain

The three-dimensional structure of a negatively stained hexagonal membrane lattice containing the light-harvesting chlorophyll a/b-protein complex and phospholipids has been determined to 30-A resolution by image reconstruction from electron micrographs. This lattice has p321 symmetry, a lattice constant of 125 A and a thickness of 75 A. The monomer is shown to be an elongated molecule about 65 A long in the dimension perpendicular to the plane of the membrane. It spans the hydrophobic domain of the membrane in an asymmetric fashion, projecting [unk]20 A from one surface and less from the other. On the basis of this image and available biochemical data, the structure of the complex in the native thylakoid membrane is proposed.

Limitation in electron transfer in photosystem I donor side mutants of Chlamydomonas reinhardtii. Lethal photo-oxidative damage in high light is overcome in a suppressor strain deficient in the assembly of the light harvesting complex

Strains of Chlamydomonas reinhardtii lacking the PsaF gene or containing the mutation K23Q within the N-terminal part of PsaF are sensitive to high light (>400 microE m(-2) s(-1)) under aerobic conditions. In vitro experiments indicate that the sensitivity to high light of the isolated photosystem I (PSI) complex from wild type and from PsaF mutants is similar. In vivo measurements of photochemical quenching and oxygen evolution show that impairment of the donor side of PSI in the PsaF mutants leads to a diminished linear electron transfer and/or a decrease of photosystem II (PSII) activity in high light. Thermoluminescence measurements indicate that the PSII reaction center is directly affected under photo-oxidative stress when the rate of electron transfer becomes limiting in the PsaF-deficient strain and in the PsaF mutant K23Q. We have isolated a high light-resistant PsaF-deficient suppressor strain that has a high chlorophyll a/b ratio and is affected in the assembly of light-harvesting complex. These results indicate that under high light a functionally intact donor side of PSI is essential for protection of C. reinhardtii against photo-oxidative damage when the photosystems are properly connected to their light-harvesting antennae.

Evidence that the intrinsic membrane protein LHCII in thylakoids is necessary for maintaining localized delta mu H+ energy coupling

This work tested the hypothesis that thylakoid localized proton-binding domains, suggested to be involved in localized delta mu H(+)-driven ATP formation, are maintained with the involvement of several membrane proteins, including the LHCII (Laszlo, J.A., Baker, G.M., and Dilley, R.A. (1984) Biochim. Biophys. Acta 764, 160-169), which comprises about 50% of the total thylakoid protein. The concept we have in mind is that several membrane proteins cooperate to shield a localized proton diffusion pathway from direct contact with the lumen, thus providing a physical barrier to H+ equilibration between the sequestered domains and the lumen. A barely mutant, chlorina f2, that lacks Chl b and does not accumulate some of the LHCII proteins, was tested for its capacity to carry out localized-proton gradient-dependent ATP formation. Two previously developed assays permit clear discrimination between localized and delocalized delta mu H+ gradient-driven ATP formation. Those assays include the effect of a permeable buffer, pyridine, on the number of single-turnover flashes needed to reach the energetic threshold for ATP formation and the more recently developed assay for lumen pH using 8-hydroxy-1,3,6-pyrene trisulfonic acid as a lumenally loaded pH-sensitive fluorescent probe. By those two criteria, the wild-type barley thylakoids revealed either a localized or a delocalized energy coupling mode under low- or high-salt storage conditions, respectively. Addition of Ca++ to the high-salt storage medium caused those thylakoids to maintain a localized energy-coupling response, as previously observed for pea thylakoids.(ABSTRACT TRUNCATED AT 250 WORDS)

Resolution of 16 to 20 chlorophyll-protein complexes using a low ionic strength native green gel system

Conventional native "green gel" systems resolve at most 10 chlorophyll-protein complexes from thylakoid membranes of higher plants and green algae. Such analyses suggest a simplicity of the thylakoid membrane that is not supported by a growing body of evidence on the heterogeneity of photosystems I and II (PSI and PSII) and their associated antennae (LHCI and LHCII). We report here the development and characterization of a low ionic strength native "green gel" system that resolves from 16 to 20, mostly large chlorophyll-protein complexes from a variety of higher plant and green algal species with very little release of free pigment. In Chlamydomonas, this system resolves multiple PSI-LHCI complexes, multiple PSII-LHCII complexes, four oligomeric LHCII complexes, as well as several low electrophoretic mobility reaction center complexes, and a number of small complexes. We have obtained similar resolution with a large number of higher plant and green algal species. We also demonstrate how this system can be used as a sort of "fingerprinting" technique to distinguish thylakoids of different species, and for the analysis of photosynthetic mutants, using the chlorophyll b-less chlorina f2 mutant of barley as an example.

Temperature sensitivity as a general phenomenon in a collection of chlorophyll-deficient mutants of sweetclover (Melilotus alba)

A collection of chlorophyll (Chl)-deficient mutants of sweetclover (Melilotus alba) with defects in eight nuclear loci were grown at 17 or 26 degrees C. Plants grown at either temperature were examined for Chl content, Chl a/b ratio, expression of the light-harvesting complex II (LHC-II) apoproteins, and protochlorophyllide (Pchlide) biosynthetic capacity. Except for the ch4 mutant, the parental strain and all mutants accumulate more Chl when grown at 26 degrees C than at 17 degrees C. The ch5 mutants, lacking Chl b under any growth condition, and the ch12 mutant showed little temperature-dependent phenotypic plasticity, whereas this was a marked phenomenon in the other mutants. The ch10 and ch11 mutants demonstrated extreme temperature sensitivity with regard to the production of Chl b and the Chl b-binding LHC-II apoproteins. When excised trifoliolates were supplemented with exogenously supplied delta-aminolevulinic acid, only the ch4 mutant was markedly impaired in the ability to produce Pchlide. These data indicate that temperature-sensitive phenotypic plasticity is a common phenomenon of chlorphyll-deficient mutants and substantiate that only a minority of Chl-deficient mutants is impaired in the biosynthesis of Chl.

Intermittent-light chloroplasts are not developmentally equivalent to chlorina f2 chloroplasts in barley

Both the chlorina f2 mutant of barley and plants grown under intermittent light have fully functional photosystems but completely lack Chl b. These two systems were compared for the presence or absence of Chl a+b-binding polypeptides using snsitive immunoblotting techniques. Both types of plants contained the apoprotein of CP29 and the minor 25 kD polypetide of LHCII, and were severely depleted in the major LHCII polypeptides. However, intermittent light plants were completely lacking LHCI polypeptides, in contrast to chlorina f2 which has at least some of them (White and Green 1987b). None of the polypeptides could be detected in dark-grown plants. This shows that intermittent light plants are not physiologically or developmentally equivalent to chlorina f2 plants. Different factors appear to be involved in controlling the synthesis/accumulation of the polypeptides of the three complexes.

Probing in vitro translation products with monoclonal antibodies to chlorophyll a/b-binding proteins of barley thylakoids

The polypeptides of the barley light-harvesting protein of photosystem I (LHCI) share certain epitopes. At least two of these common epitopes are present in chlorophyll a/b-protein 1 (Chla/b-P1 = CP29), as shown by cross-reacting monoclonal antibodies (14). These antibodies were employed for immunological identification of polypeptides translated in vitro in an mRNA-dependent cell-free rabbit reticulocyte lysate. The monoclonal antibody CMpLHCI:2 precipitated only one polypeptide of molecular weight 28 kD from in vitro translates primed with polyA+ RNA. No 28 kD precipitation band was found, if this antibody was mixed with a PSI-200 preparation before it was added to the translate. The translational capacity of the LHCI transcripts isolated from 12 hours greened barley was much higher than those isolated from 6 hours greened barley. Transcripts for LHCI polypeptides were also found among the polyA+ RNA of the mutant viridis-k23, which is devoid of LHCI polypeptides in its thylakoid membranes. The monoclonal antibody CMpCh1a/b-P1:1 precipitated a polypeptide of molecular weight 31 kD from in vitro translates primed with polyA+ RNA. Thus, the cross-reactivity the two antibodies show with the mature proteins is not found when the antibodies are reacted with the precursor proteins.

Immunological characterization of chlorophyll a/b-binding proteins of barley thylakoids

Monoclonal antibodies have been raised against the light-harvesting chlorophyll a/b-binding proteins of photosystem I (LHCI) using a photosystem (PS) I preparation (PSI-200) wild-type from barley (Hordeum vulgare L. cv. Svaløf's Bonus) as the antigen. These antibodies cross-reacted with a minor light-harvesting chlorophyll a/b-protein of PSII (Chla/b-P1=CP29), but not with the major one, LHCII (=Chla/b-P2(**)). Similarly, a monoclonal antibody to Chla/b-P1, elicited by a PSII preparation as the antigen, cross-reacted with LHCI, but not LHCII. This explains why an antigen consisting of LHCII, free of LHCI, but contaminated with Chla/b-P1, can elicit antibodies which cross-react with LHCI. Immunoblot assays showed that LHCI and Chla/b-P1 have at least two epitopes in common. Immunogold labelling of thin-sectioned wild-type thylakoids confirmed a preferential localisation of Chla/b-P1 in grana partition membranes and LHCI in stroma lamellae. The presence of LHCI was demonstrated in barley mutants lacking the PSI reaction centre (viridis-zb (63)) and chlorophyll b (chlorina-f2), and was correlated with the presence of long-wavelength (730 nm) fluorescence emission at 77 K. The mutant viridis-k (23), which has a 77 K long-wavelength fluorescence peak at 720 nm, was shown by immune-blot assay to lack LHCI, although Chla/b-P1 was present.

Polypeptides belonging to each of the three major chlorophyll a + b protein complexes are present in a chlorophyll-b-less barley mutant

Polypeptides of the three major chlorophyll a + b protein complexes were detected in a chlorophyll-b-less barley mutant (chlorina f2) using immunological techniques. Antibodies to CP Ia, a photosystem I complex containing both the reaction center (CP I) and the chlorophyll a + b antenna (LHCI), detected substantial amounts of LHCI polypeptides in mutant thylakoids. Some polypeptides of the two photosystem-II-associated chlorophyll a + b complexes, CP 29 and LHCII, were also detected using antibodies raised against these complexes. The CP 29 apoprotein and the minor 25-kDa polypeptide of LHCII were present in amounts that could be seen by Coomassie blue staining. In contrast, the two major polypeptides of LHCII were greatly diminished in amount, and one of them may be completely absent. These data suggest that the absence of chlorophyll b may have differing effects on the synthesis, processing or turnover of the various chlorophyll a + b binding polypeptides. They also show that these polypeptides can be inserted into thylakoids in the absence of Chl b, and that significant amounts of some of them are accumulated in the mutant thylakoids.

Chloroplast phosphoproteins: phosphorylation of a 12-kDa stromal protein by the redox-controlled kinase of thylakoid membranes

Activation of the redox-controlled protein kinase of thylakoid membranes is detectable in vivo by measuring radioisotope incorporation into the light-harvesting Chl a/b protein and four photosystem II proteins (8.3, 32, 34, and 44 kDa). In normal barley leaves, the kinase is active under both aerobic and anaerobic (N2) conditions, but in the Chl b-less chlorina f2 mutant it is active only under anaerobic conditions. The responsiveness of this enzyme in the mutant to changes in the gas phase has been exploited to distinguish its protein substrates from those of other leaf protein kinases. Most of the soluble phosphoproteins of normal and mutant leaves (including a conspicuously labeled 67-kDa polypeptide) are labeled equally under both aerobic and anaerobic conditions, indicating that they are not substrates of the redox-controlled protein kinase. The major exception is a 12-kDa phosphoprotein, which is labeled in the mutant only under anaerobic conditions. The 67- and 12-kDa phosphoproteins are located in the chloroplast and are labeled when isolated organelles are incubated with [32P]orthophosphate in the light. When thylakoids and stroma are prepared from chloroplasts and are incubated with [gamma-32P]ATP in vitro, the 12-kDa protein is phosphorylated in the thylakoid preparation and then released from the membranes into the medium. The electron transport inhibitor diuron blocks activation of the redox-controlled kinase and prevents phosphorylation of the 12-kDa protein, which is thus the first example of a soluble protein to be phosphorylated by the thylakoid-bound protein kinase. The 67-kDa protein is phosphorylated by a distinct stromal kinase whose activity is not sensitive to diuron.

Evidence for a light-harvesting chlorophyll a-protein complex in a chlorophyll b-less barley mutant

Chloroplasts of a chlorophyll (Chl) b-less barley mutant were solubilized with digitonin and fractionated by polyacrylamide gel electrophoresis with sodium deoxycholate in the running buffer. By this procedure, in contrast to using sodium dodecylsulfate (SDS) for solubilization, a Chl a-protein analogous to the major light-harvesting Chl a-b protein complex from wildtype chloroplasts was recovered. This mutant Chl a-protein comprises about fifty percent of the total Chl a, and is very similar in carotenoid, amino acid, protein and polypeptide composition to the major wildtype antenna Chl a-b protein. The only major differences we have found is its instability in the presence of SDS and sensitivity to protease action. Even with deoxycholate, the mutant Chl a complex often dissociates during electrophoresis into two green bands. The lack of Chl b appears to affect the normal organization of Chl a and protein in such a way as to render the complex more unstable.

Monoclonal antibodies to the light-harvesting chlorophyll a/b protein complex of photosystem II

A collection of 17 monoclonal antibodies elicited against the light-harvesting chlorophyll a/b protein complex which serves photosystem II (LHC-II) of Pisum sativum shows six classes of binding specificity. Antibodies of two of the classes recognize a single polypeptide (the 28- or the 26- kD polypeptides), thereby suggesting that the two proteins are not derived from a common precursor. Other classes of antibodies cross-react with several polypeptides of LHC-II or with polypeptides of both LHC-II and the light-harvesting chlorophyll a/b polypeptides of photosystem I (LHC-I), indicating that there are structural similarities among the polypeptides of LHC-II and LHC-I. The evidence for protein processing by which the 26-, 25.5-, and 24.5-kD polypeptides are derived from a common precursor polypeptide is discussed. Binding studies using antibodies specific for individual LHC-II polypeptides were used to quantify the number of antigenic polypeptides in the thylakoid membrane. 27 copies of the 26-kD polypeptide and two copies of the 28-kD polypeptide were found per 400 chlorophylls. In the chlorina f2 mutant of barley, and in intermittent light-treated barley seedlings, the amount of the 26-kD polypeptide in the thylakoid membranes was greatly reduced, while the amount of 28-kD polypeptide was apparently not affected. We propose that stable insertion and assembly of the 28-kD polypeptide, unlike the 26-kD polypeptide, is not regulated by the presence of chlorophyll b.

Carotenoid-deficient maize seedlings fail to accumulate light-harvesting chlorophyll a/b binding protein (LHCP) mRNA

Yellow leaves of chlorophyll-deficient seedlings and white leaves of carotenoid-deficient seedlings contain no detectable light-harvesting chlorophyll a/b binding proteins (LHCP). Chlorophyll-deficient leaves contain plastids which are arrested in development prior to chloroplast formation [Mascia, P.N. and Robertson, D.S. (1978) Planta (Berl.) 143, 207-211] while carotenoid-deficient leaves contain plastids which are arrested in development at a rudimentary stage [Bachmann, M. D., Robertson, D.S., Bowen, C.C., and Anderson, I.C. (1967) J. Ultrastruc. Res. 21, 41-60]. Chlorophyll-deficient leaves have normal levels of nuclear-encoded LHCP mRNA while carotenoid-deficient leaves contain only trace amounts of LHCP mRNA. Similar results were obtained with carotenoid deficiencies caused by nuclear gene mutations and by treatment with the herbicide norflurazon which blocks carotenoid biosynthesis. We conclude that events at early stages of plastid development influence the accumulation of a nuclear-encoded mRNA.

Investigations of the role of the main light-harvesting chlorophyll-protein complex in thylakoid membranes. Reconstitution of depleted membranes from intermittent-light-grown plants with the isolated complex

The functions of the light-harvesting complex of photosystem II (LHC-II) have been studied using thylakoids from intermittent-light-grown (IML) plants, which are deficient in this complex. These chloroplasts have no grana stacks and only limited lamellar appression in situ. In vitro the thylakoids showed limited but significant Mg2+-induced membrane appression and a clear segregation of membrane particles into such regions. This observation, together with the immunological detection of small quantities of LHC-II apoproteins, suggests that the molecular mechanism of appression may be similar to the more extensive thylakoid stacking seen in normal chloroplasts and involve LHC-II polypeptides directly. To study LHC-II function directly, a sonication-freeze-thaw procedure was developed for controlled insertion of purified LHC-II into IML membranes. Incorporation was demonstrated by density gradient centrifugation, antibody agglutination tests, and freeze-fracture electron microscopy. The reconstituted membranes, unlike the parent IML membranes, exhibited both extensive membrane appression and increased room temperature fluorescence in the presence of cations, and a decreased photosystem I activity at low light intensity. These membranes thus mimic normal chloroplasts in this regard, suggesting that the incorporated LHC-II interacts with photosystem II centers in IML membranes and exerts a direct role in the regulation of excitation energy distribution between the two photosystems.

Freeze-fracture analysis of membrane appression and protein segregation in model membranes containing the chlorophyll-protein complexes from chloroplasts

Cation-induced membrane appression and lateral segregation of chlorophyll-protein complexes have been investigated by freeze-fracture analysis of model membranes containing photosystem 1 and the light-harvesting complex of photosystem 2. In light-harvesting complex proteoliposomes, cations caused extensive membrane adhesion and a segregation of protein into appressed regions. A marked flattening of the appressed membranes, sometimes together with a co-alignment of the particles on the opposing membrane faces, strongly suggests a direct transmembrane attraction between the protein particles. Photosystem 1 membranes were not appressed by cations but some clustering of the particles occurred, together with their exclusion from some regions of the lipid. By incorporating dipalmitoylglycerophosphocholine into the membranes, it is shown that a similar exclusion of the particles can occur due to liquid-crystalline to gel state transitions of the lipids. Proteoliposomes containing both the light-harvesting complex and photosystem 1 displayed cation-induced membrane appression, but only between regions containing the light-harvesting complex. Photosystem 1 was largely confined to unappressed membranes. Destacking occurred at low salt concentrations irrespective of whether photosystem 1 was present, showing that in proteoliposomes, and probably in thylakoids, this process does not require the presence of highly charged complexes from unappressed regions.