The interaction between the 33 kDa manganese-stabilising protein and the D1 /D2 cytochrome b -559 complex

Mutations of arginine 64 within the putative Ca(2+)-binding lumenal interhelical a-b loop of the photosystem II D1 protein disrupt binding of the manganese stabilizing protein and cytochrome c(550) in Synechocystis sp. PCC6803

Mutations D1-R64E, D1-R64Q, and D1-R64V in the putative calcium-binding lumenal interhelical a-b loop of the photosystem II (PSII) D1 protein were characterized in terms of impact on growth, extrinsic protein binding, photoactivation, and properties of the H(2)O-oxidation complex. The D1-R64E charge reversal mutation greatly weakened the binding of the extrinsic manganese-stabilizing protein (MSP) and, to a considerably lesser extent, weakened the binding of cytochrome c(550) (c550). Both D1-R64Q and D1-R64E exhibited an increased requirement for Ca(2+) in the cell growth medium. Bare platinum electrode measurements of O(2)-evolving membranes showed a retarded appearance of O(2) following single turn-over flashes, especially in the case of the D1-R64E mutant. The D1-R64E mutant also had a pronounced tendency to lose O(2) evolution activity in the dark and exhibited an increased relative quantum yield of photoactivation, which are characteristics shared by mutants that lack extrinsic proteins. S(2) and S(3) decay measurements in the isolated membranes indicate that D1-R64E and D1-R64Q have faster decays of these higher S-states as compared to the wild-type. However, fluorescence decay in the presence of DCMU, which monitors primarily Q(A)(-) charge recombination with PSII donors, showed somewhat slower decays. Taken together, the fluorescence and S-state decay indicate that the midpoint of either Q(B)(-) has been modified to be more negative in the mutants or that a recombination path presumably involving either Q(B)(-) or Y(D) has become kinetically more accessible.

Responses to bleaching herbicides by leaf chloroplasts of maize plants grown at different temperatures

The effects of growth temperature on chloroplast responses to norflurazon and amitrole, two herbicides inhibiting carotenogenesis, at phytoene desaturation and lycopene cyclization, respectively, were studied in leaves of maize plants grown at 20 degrees C and 30 degrees C in light. At the lower temperature both chemicals caused severe photo-oxidative damage to chloroplasts. In organelles of norflurazon-treated leaves neither carotenoids nor chlorophylls were detectable and the thylakoid system was dismantled. In organelles of amitrole-treated leaves lycopene was accumulated, but small quantities of beta-carotene and xanthophylls were also produced. Moreover, some chlorophyll and a few inner membranes still persisted, although these latter were disarranged, lacking essential protein components and devoid of photosynthetic function. The increase in plant growth temperature to 30 degrees C did not change the norflurazon effects on carotenoid synthesis and the photo-oxidative damage suffered by chloroplasts. By contrast, in organelles of amitrole-treated leaves a large increase in photoprotective carotenoid biosynthesis occurred, with a consequent recovery of chlorophyll content, ultrastructural organization and thylakoid composition and functionality. This suggests that thermo-modulated steps could exist in the carotenogenic pathway, between the points inhibited by the two herbicides. Moreover it shows that, unlike C(3) species, C(4) species, such as maize, can express a strong tolerance to herbicides like amitrole, when supplied to plants growing at their optimum temperature conditions.

Biochemical and functional properties of photosystem II in agranal membranes from maize mesophyll and bundle sheath chloroplasts

We have studied the occurrence and organization of photosystem II (PSII) in bundle sheath thylakoids and stroma lamellae from maize. As shown by non-denaturing lauryl beta-D- iminopropionidate (Deriphat)/PAGE, PSII exists in a dimeric form in grana membranes. In bundle sheath and stroma lamellae, however, only a monomeric form was found. Based on immunotitration data, we estimated the stoichiometry of the individual components of the PSII core complex and antenna systems. In stroma lamellae, all PSII antenna complexes had a stoichiometry similar to that in grana membranes, with the exception of light-harvesting complex II (LHCII) that was somewhat over-represented, while the minor antenna complexes CP26 and CP29 were under-represented. In bundle sheath, the amount of LHCII was approximately eight times higher than expected with respect to D1. The 33-kDa protein of the oxygen-evolving enhancer polypeptides was not detectable nor was the ferredoxin-NADP+ reductase, thus strongly suggesting that no significant linear electron transport occurs in bundle sheath thylakoids. Fluorescence induction data suggest that most of the PSII reaction centers in bundle sheath and stroma lamellae sustain electron transport towards a secondary acceptor pool. Stromal PSII centers are only weakly inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), whereas, unexpectedly, dichlorobenzoquinone and methyl viologen had a pronounced inhibitory effect of the QA- reoxidation. An additional specificity of these centers is the slow rate (50-ms range) of the QA to QB electron transfer. The amplitude of variable fluorescence found in stroma lamellae can only account for a small fraction (1-2%) of the variable fluorescence of whole thylakoids. This suggests that stromal PSII cannot be solely responsible for the slow beta-phase of the induction kinetics.

Identification of the psbH gene product as a 6 kDa phosphoprotein in the cyanobacterium Synechocystis 6803

The product of the psbH gene has been identified in Synechocystis 6803 thylakoid membranes as a 6 kDa phosphoprotein. This protein becomes phosphorylated in vitro despite the fact that in cyanobacteria it is truncated at the N-terminus such that the phosphorylation site identified in the higher plant protein is missing. Phosphorylation occurred both in the light and in the dark but was inhibited by oxidising conditions, DCMU and zinc ions. The cyanobacterial 6 kDa phosphoprotein degrades when the membranes are subjected to high intensity illumination.

Investigation of the neighbour relationships between photosystem II polypeptides in the two types of isolated reaction centres (D1/D2/cytb559 and CP47/D1/D2/cyt b559 complexes)

The nearest neighbour relationships within the D1/D2/cyt b559 complex (PSIIRC) and the CP47/D1/D2/cyt b559 complex (RC-CP47) were investigated by using different length bifunctional crosslinking agents. The crosslinking products were identified by immunoblotting with polyclonal antibodies and by two-dimensional gel electrophoresis. Seven products (CP47/D2, D1/D2/alpha, D1/D2, D2/alpha, D1/alpha, alpha/alpha, alpha/beta) have been revealed in both complexes. The crosslinking of both complexes does not increase their photostability. The photocrosslinking products (D1/alpha and D2/alpha) appeared under illumination of complexes with light of high intensity.

Light-induced degradation of D2 protein in isolated photosystem II reaction center complex

When isolated photosystem II reaction centers from spinach are exposed to photoinhibitory light in the presence of an electron acceptor, breakdown products of the D2 protein at 28, 25, 23, 18, 9, 5 and 4.5 kDa are detected by immunoblotting with a monospecific anti-D2 polyclonal antibody. In a time-course experiment the 23 and 4.5 kDa fragments show a transient appearance, whilst the others are photoaccumulated. The regions of the D2 protein containing the cleavage sites for the 28 and 18 kDa photoinduced fragments have been identified. Significant degradation of D2 takes place only in the presence of an electron acceptor, and breakdown of the protein is partially prevented by serine-type protease inhibitors.

Interaction of CPa-1 with the manganese-stabilizing protein of photosystem II: identification of domains cross-linked by 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide

The structural organization of photosystem II proteins has been investigated by use of the zero-length protein cross-linking reagent 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide and monoclonal and polyclonal antibody reagents. Photosystem II membranes were treated with 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide which cross-links amino groups to carboxyl groups which are in van der Waals contact. This treatment did not affect the oxygen evolution rates of these membranes and increased the retention of oxygen evolution after CaCl2 washing. Analysis of the proteins cross-linked by this treatment indicated that two cross-linked species with apparent molecular masses of 95 and 110 kDa were formed which cross-reacted with antibodies against both the 33-kDa manganese-stabilizing protein and the chlorophyll protein CPa-1. Cleavage of the 110-kDa cross-linked species with cyanogen bromide followed by N-terminal sequence analysis was used to identify the peptide fragments of CPa-1 and the manganese-stabilizing protein which were cross-linked. Two cyanogen bromide fragments were identified with apparent molecular masses of 50 and 25 kDa. N-Terminal sequence analysis of the 50-kDa cyanogen bromide fragment indicates that this consists of the C-terminal 16.7-kDa fragment of CPa-1 and the intact manganese-stabilizing protein. This strongly suggests that the manganese-stabilizing protein is cross-linked to the large extrinsic loop domain of CPa-1. N-Terminal analysis of the 25-kDa cyanogen bromide fragment indicates that this consists of the C-terminal 16.7-kDa peptide of CPa-1 and the N-terminal 8-kDa peptide of the manganese-stabilizing protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Stabilisation of PS-II-mediated electron transport in oxygen-evolving PS II core preparations by the addition of compatible co-solutes

Addition of high concentrations of compatible co-solutes such as sugars, sugar alcohols and polyols has recently been shown to lead to marked increases in the thermal stability of oxygen-evolution in chloroplasts (Williams et al. (1992) Biochim. Biophys. Acta 1099, 137-144). In this paper, a similar stabilisation is demonstrated for oxygen-evolving PS II core preparations. The presence of such co-solutes appears, however, to have no ability to stabilise PS II reaction-centre preparations against heat-induced changes in their absorption spectrum. Nor do they protect electron transport from artificial electron donors in PS II core preparations lacking the extrinsic 33 kDa polypeptide of the oxygen-evolution system. Measurements performed on core preparations retaining the 33 kDa polypeptide but lacking the 17 kDa and 23 kDa polypeptides indicate that the co-solutes protect PS-II-mediated electron transport by stabilising the binding of the 33 kDa polypeptide to the core complexes. These findings are discussed in terms of an extension of the general principles underlying the Hofmeister effect observed for soluble proteins to the stabilisation of photosynthetic membrane preparations.

Breakdown of the photosystem II reaction center D1 protein under photoinhibitory conditions: identification and localization of the C-terminal degradation products

Illumination of a suspension of thylakoids with light at high intensity causes inhibition of the photosystem II electron transport activity and loss from the membrane of the D1 protein of the photosystem II reaction center. Impairment of the electron transport activity and depletion of D1 protein from the thylakoid membrane of pea were investigated with reference to the presence or absence of oxygen in the suspension. The breakdown products of the D1 protein were identified by immunoblotting with anti-D1 polyclonal antibodies which were proven to recognize mainly the C-terminal region of the protein. The results obtained show that (i) the light-induced inactivation of the photosystem II electron transport activity under anaerobic conditions is faster than in the presence of oxygen; (ii) depletion of D1 protein is observed on a longer time scale with respect to loss of electron transport activity and is faster when photoinhibition is performed in the presence of oxygen; (iii) C-terminal fragments of D1 are only observed when photoinhibition is carried out anaerobically and are mainly localized in the stroma-exposed regions; and (iv) the fragments observed after anaerobic photoinhibition are quickly degraded on further illumination of the thylakoid suspension in the presence of oxygen.

Chlorophyll levels in the pigment-binding proteins of photosystem II. A study based on the chlorophyll to cytochrome ratio in different photosystem II preparations

The chlorophyll levels in pigment proteins of photosystem II were investigated by using photosystem II preparations with different levels of complexity. Based on the assumption that there is 1 cytochrome b559 per reaction centre it has been found that oxygen-evolving complexes containing CP26 and CP29 bind 42 chlorophyll molecules. When CP26 and CP29 are stripped away, the resulting PSII cores bind 30 chlorophyll molecules while CP43-less cores bind approximately 18 chlorophylls. It is therefore concluded that CP47 and CP43 bind 9-12 molecules of chlorophyll a and the D1/D2 complex binds 6 chlorophylls. Taken together CP26 and CP29 bind about 12 chlorophyll molecules.

The structure and function of CPa-1 and CPa-2 in Photosystem II

This review presents a summary of recent investigations examining the structure and function of the chlorophyll-proteins CPa-1 (CP47) and CPa-2 (CP43). Comparisons of the derived amino acid sequences of these proteins suggest sites for chlorophyll binding and for interactions between these chlorophyll-proteins and other Photosystem II components. Hydropathy plot analysis of these proteins allows the formulation fo testable hypotheses concerning their topology and orientation within the photosynthetic membrane. The role of these chlorophyll-proteins as interior light-harvesting chlorophyll-a antennae for Photosystem II is examined and other possible additional roles for these important Photosystem II components are discussed.

Lumen-side topography of the alpha-subunit of the chloroplast cytochrome b-559

Removal of the extrinsic 33 kDa polypeptide increased the accessibility to trypsin of a COOH-terminal tridecapeptide epitope of the alpha subunit of cytochrome b-559 (psbE gene product). The sensitivity of the cytochrome epitope to trypsin was not measurably affected by removal of the 16 and 23 kDa extrinsic polypeptides, nor increased by removal of the OEC manganese along with the 33 kDa protein. While protecting alpha-cytochrome b-559 against trypsin, the 33 kDa protein is also proteolyzed, suggesting the possibility of an additional protein component involved in the shielding of the cytochrome. Shielding of the COOH-terminal epitope of alpha-cytochrome b-559 by the OEC 33 kDa protein implies that these COOH-terminal chains of the cytochrome are part of a protein network in the lumen space near the photosystem II reaction center. This network may contain residues that are involved in the binding of essential OEC metal ions.

Epitope mapping of the monoclonal antibody FAC2 on the apoprotein of Cpa-1 in photosystem II

Using a combination of cyanogen bromide cleavage and endoproteinase digestion we have shown that the putative epitope for the monoclonal antibody FAC2 lies in the region 360Pro(-391)Ser on the apoprotein of CPa-1. This region lies entirely within the large extrinsic loop of this protein. We have shown previously that the epitope of FAC2 becomes exposed in oxygen-evolving membranes upon treatment with alkaline Tris which releases all four of the manganese associated with the oxygen-evolving site of photosystem II. The epitope is not exposed, however, after CaCl(2) treatment and exposure to low concentrations of chloride, conditions which lead to the release of two of the four manganeses associated with the oxygen-evolving site. These results suggest that, upon release of the chloride-insensitive manganese from photosystem II membranes, a conformational change occurs which leads to the exposure of 360Pro(-391)Ser on CPa-1 to the monoclonal antibody FAC2.