Lipid-protein interactions in thylakoid membranes of chilling-resistant and -sensitive plants studied by spin label electron spin resonance spectroscopy

Lipid-protein interactions in thylakoid membranes from lettuce, pea, tomato, and cucumber have been studied using spin-labeled analogues of the thylakoid membrane lipid components, monogalactosyl diglyceride and phosphatidylglycerol. The electron spin resonance spectra of the spin-labeled lipids all consist of two components, one corresponding to the fluid lipid environment in the membranes and the other to the motionally restricted lipids interacting with the integral membrane proteins. Comparison of the spectra from the same spin label in thylakoid membranes from different plants shows that the overall lipid fluidity in the membranes decreases with chilling sensitivity. Spectral subtraction has been used to quantitate the fraction of the membrane lipids in contact with integral membrane proteins. Thylakoid membranes of cucumber, a typical chilling-sensitive plant, have been found to have a higher proportion of motionally restricted lipids and a different lipid selectivity for lipid-protein interaction, as compared with those of pea, a typical chilling-resistant plant. This correlation with chilling sensitivity holds generally for the different plants studied. It seems likely that the chilling sensitivity in thylakoid membranes is not determined by lipid fluidity alone, but also by the lipid-protein interactions which could affect protein function in a more direct manner.     

Selectivity of interaction of phospholipids with bovine spinal cord myelin basic protein studied by spin-label electron spin resonance

The selectivity of interaction between bovine spinal cord myelin basic protein (MBP) and eight different spin-labeled lipid species in complexes with dimyristoylphosphatidylglycerol (DMPG) and between spin-labeled phosphatidylglycerol and spin-labeled phosphatidylcholine in complexes of MBP with various mixtures of DMPG and dimyristoylphosphatidylcholine (DMPC) has been studied by electron spin resonance (ESR) spectroscopy. In DMPC/DMPG mixtures, the protein binding gradually decreased with increasing mole fraction of DMPC in a nonlinear fashion. The lipid-protein binding assays indicated a preferential binding of the protein to phosphatidylglycerol relative to phosphatidylcholine without complete phase separation of the two lipids. The outer hyperfine splittings (2Amax) of both phosphatidylglycerol and phosphatidylcholine labeled at C-5 of the sn-2 chain (5-PGSL and 5-PCSL, respectively) were monitored in the lipid-protein complexes as a function of the mole fraction of DMPC. The increases in the value of Amax induced on binding of the protein were larger for 5-PGSL than for 5-PCSL, up to 0.25 mole fraction of DMPC. Beyond this mole fraction the spectral perturbations induced by the protein were similar for both lipid labels. The ESR spectra of phosphatidylglycerol and phosphatidylcholine labeled at C-12 of the sn-2 chain were two component in nature, indicating indicating a direct interaction of the protein with the lipid chains, at mole fractions of DMPC up to 0.25. Quantitation of the motionally restricted spin-label population by spectral subtraction again indicated a preferential interaction of the protein with phosphatidylglycerol relative to phosphatidylcholine. Up to DMPC mode fractions of 0.25, the microenvironment of the protein was enriched in DMPG.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spin label saturation transfer ESR studies of protein-lipid interactions in Photosystem II-enriched membranes

Saturation transfer ESR has been used to study the dynamic behaviour of lipids in the appressed regions of thylakoid membranes from pea seedlings. Four different phospho- and galacto-lipid spin labels (phosphatidylcholine labelled at the 12 or 14 C-atom positions of the sn-2 chain, phosphatidylglycerol labelled at the 14-position of the sn-2 chain, and monogalactosyldiacylglycerol labelled at the 12-position of the sn-2 chain) were used to probe the lipid environment in photosystem II-enriched membranes prepared by detergent extraction. The ESR spectra show that the majority of the lipid in these preparations is strongly motionally restricted. Values for the effective rotational correlation times of the labelled chains were deduced from the lineheight ratios and integrals of thhe saturation transfer ESR spectra. The effective rotational correlation times were found to be in the 10⁵ range, indicating a very low lipid chain mobility which correlates with the low lipid content of these preparations. Comparison of the effective rotational correlation times deduced from the different diagnostic regions of the spectrum revealed little anisotropy in the chain mobility, indicating that the dominant motional mode was trans-gauche isomerization. The effective rotational correlation times deduced from the spectral integrals were similar to those deduced from the lineheight ratios, consistent with the absence of any appreciable fluid lipid component in these preparations. The results also indicate some selectivity of interaction between the lipid species, with phosphatidylcholine exhibiting appreciably slower motion than either phosphatidylglycerol or monogalactosyldiacylglycerol.     

Stoichiometry and specificity of lipid-protein interaction with myelin proteolipid protein studied by spin-label electron spin resonance

The interaction of spin-labeled lipids with the myelin proteolipid apoprotein in complexes with dimyristoylphosphatidylcholine of varying lipid/protein ratios has been studied with electron spin resonance spectroscopy. A first shell of approximately 10 lipids per 25 000-dalton protein is found to be motionally restricted by the protein interface. This stoichiometry is consistent with a hexameric arrangement of the protein in the membrane. A selectivity of the various spin-labeled lipids for the motionally restricted component at the protein interface is found in the order stearic acid greater than phosphatidic acid greater than cardiolipin approximately greater than phosphatidylserine greater than phosphatidylglycerol approximately equal to phosphatidylcholine greater than phosphatidylethanolamine greater than androstanol approximately greater than cholestane.     

Association of spin-labeled lipids with beta-barrel proteins from the outer membrane of Escherichia coli

The interaction of spin-labeled lipids with beta-barrel transmembrane proteins has been studied by the electron spin resonance (ESR) methods developed for alpha-helical integral proteins. The outer membrane protein OmpA and the ferrichrome-iron receptor FhuA from the outer membrane of Escherichia coli were reconstituted in bilayers of dimyristoylphosphatidylglycerol. The ESR spectra from phosphatidylglycerol spin labeled on the 14-C atom of the sn-2 chain contain a second component from motionally restricted lipids contacting the intramembranous surface of the beta-barrel, in addition to that from the fluid bilayer lipids. The stoichiometry of motionally restricted lipids, 11 and 32 lipids/monomer for OmpA and FhuA, respectively, is constant irrespective of the total lipid/protein ratio. It is proportional to the number of transmembrane beta-strands, eight for OmpA and 22 for FhuA, and correlates reasonably well with the intramembranous perimeter of the protein. Spin-labeled lipids with different polar headgroups display a differential selectivity of interaction with the two proteins. The more pronounced pattern of lipid selectivity for FhuA than for OmpA correlates with the preponderance of positively charged residues facing the lipids in the extensions of the beta-sheet and shorter interconnecting loops on the extracellular side of FhuA.     

Ganglioside-protein interactions: spin-label electron spin resonance studies with (Na+,K+)-ATPase membranes

Lipid-protein interactions in (Na+,K+)-ATPase-rich membranes from Squalus acanthias have been studied using spin-labeled derivatives of the mono- and disialogangliosides GM1, GM2, GM3, and GD1b, in conjunction with electron spin resonance (ESR) spectroscopy. Ganglioside-protein interactions are revealed by the presence of a second component in the ESR spectra of the membranes in addition to a component that corresponds closely to the ESR spectra obtained from dispersions of the extracted membrane lipids. This second component corresponds to spin-labeled gangliosides whose chain motion is significantly restricted relative to that of the fluid lipids in the membrane or the lipid extract. A small selectively for the motionally restricted component associated with the protein is found in the order GD1b greater than GM1 approximately equal to GM2 approximately equal to GM3. Comparison with previous results from spin-labeled phospholipids in the same system [Esmann, M., Watts, A., & Marsh, D. (1985) Biochemistry 24, 1386-1393] shows that the spin-labeled monosialogangliosides GM1, GM2, and GM3 display little selectivity in the lipid-protein interaction relative to spin-labeled phosphatidylcholine. The spectral characteristics of both the fluid and motionally restricted spin-labeled components differ very significantly, however, between the gangliosides and the phospholipids. The outer hyperfine splitting of the motionally restricted component is smaller for the gangliosides than for the phospholipids, indicating a smaller degree of motional restriction on interaction of the ganglioside lipid chains with the protein.(ABSTRACT TRUNCATED AT 250 WORDS)     

Structural and functional consequences of galactolipids on thylakoid membrane organization

Photosynthetic membranes of higher plant chloroplasts are composed primarily of polar, but uncharged, galactolipids unlike most mammalian membranes which contain large amounts of phosphatidylcholine. It is unclear what role(s) the galactolipids play in maintaining the differentiated thylakoid membranes, or in stabilizing the photosynthetically active enzyme complexes. Some of the membrane complexes show no lipid selectivity for maintaining structural or functional integrity. Others are poisoned or dissociated in the presence of high concentrations of a trace lipid class. The efficiency of energy transfer and the reconstitution of protein complexes into liposomes are dependent on the lipid class employed. The lipids are asymmetrically arranged along and across the thylakoid membranes but not as distinctly as the proteins.Abbreviations DGDG digalactosyldiglyceride - MGDG monogalactosyldiglyceride - SQDG sulfoquinovosyldiglyceride - PG phosphatidylglycerol - PC phosphatidylcholine - PE phosphatidylethanolamine - PSI photosystem I - PSII photosystem II - LHC chlorophylla/b lightharvesting complex - cytb ₆ f cytochromeb ₆ f complex - CF₀/CF₁ coupling factor ATPase - DCIP 2,6-dichlorophenolindophenol - LRa galactolipase fromRhizopus arrhis     

Alpha-synuclein association with phosphatidylglycerol probed by lipid spin labels

Alpha-synuclein is a small presynaptic protein, which is linked to the development of Parkinson's disease. Alpha-synuclein partitions between cytosolic and vesicle-bound states, where membrane binding is accompanied by the formation of an amphipathic helix in the N-terminal section of the otherwise unstructured protein. The impact on alpha-synuclein of binding to vesicle-like liposomes has been studied extensively, but far less is known about the impact of alpha-synuclein on the membrane. The interactions of alpha-synuclein with phosphatidylglycerol membranes are studied here by using spin-labeled lipid species and electron spin resonance (ESR) spectroscopy to allow a detailed analysis of the effect on the membrane lipids. Membrane association of alpha-synuclein perturbs the ESR spectra of spin-labeled lipids in bilayers of phosphatidylglycerol but not of phosphatidylcholine. The interaction is inhibited at high ionic strength. The segmental motion is hindered at all positions of spin labeling in the phosphatidylglycerol sn-2 chain, while still preserving the chain flexibility gradient characteristic of fluid phospholipid membranes. Direct motional restriction of the lipid chains, resulting from penetration of the protein into the hydrophobic interior of the membrane, is not observed. Saturation occurs at a protein/lipid ratio corresponding to approximately 36 lipids/protein added. Alpha-synuclein exhibits a selectivity of interaction with different phospholipid spin labels when bound to phosphatidylglycerol membranes in the following order: stearic acid > cardiolipin > phosphatidylcholine > phosphatidylglycerol approximately phosphatidylethanolamine > phosphatidic acid approximately phosphatidylserine > N-acyl phosphatidylethanolamine > diglyceride. Accordingly, membrane-bound alpha-synuclein associates at the interfacial region of the bilayer where it may favor a local concentration of certain phospholipids.     

Characteristics of chloroplast thylakoid lipid composition associated with resistance to triazine herbicides

A detailed comparison of the polar-lipid composition of chloroplast thylakoid membranes isolated from triazine-susceptible and triazine-resistant biotypes of Chenopodium album, Senecio vulgaris, Poa annua and Amaranthus retroflexus has been carried out. No major differences in the composition of the bulk lipid matrix were found except for a slightly higher monogalactosyldiacylglycerol to digalactosyldiacylglycerol ratio in resistant compared with susceptible biotypes. There was, however, in the case of resistant plants a higher level of phosphatidylglycerol-containing transhexadecenoic acid in membrane fractions enriched in photosystem two. It is concluded that although the minor differences could contribute to triazine resistance it is more likely that they reflect secondary alterations in membrane organisation associated with changes in relative levels of pigment-protein complexes.Abbreviations DGDG digalactosyldiacylglycerol - MGDG monogalactosyldiacylglycerol - PG phosphatidylglycerol - PSII photosystem two     

Chloroplast biogenesis. Regulation of lipid transport to the thylakoid in chloroplasts isolated from expanding and fully expanded leaves of pea

To study the regulation of lipid transport from the chloroplast envelope to the thylakoid, intact chloroplasts, isolated from fully expanded or still-expanding pea (Pisum sativum) leaves, were incubated with radiolabeled lipid precursors and thylakoid membranes subsequently were isolated. Incubation with UDP[(3)H]Gal labeled monogalactosyldiacylglycerol in both envelope membranes and digalactosyldiacylglycerol in the outer chloroplast envelope. Galactolipid synthesis increased with incubation temperature. Transport to the thylakoid was slow below 12 degrees C, and exhibited a temperature dependency closely resembling that for the previously reported appearance and disappearance of vesicles in the stroma (D.J. Morré, G. Selldén, C. Sundqvist, A.S. Sandelius [1991] Plant Physiol 97: 1558-1564). In mature chloroplasts, monogalactosyldiacylglycerol transport to the thylakoid was up to three times higher than digalactosyldiacylglycerol transport, whereas the difference was markedly lower in developing chloroplasts. Incubation of chloroplasts with [(14)C]acyl-coenzyme A labeled phosphatidylcholine (PC) and free fatty acids in the inner envelope membrane and phosphatidylglycerol at the chloroplast surface. PC and phosphatidylglycerol were preferentially transported to the thylakoid. Analysis of lipid composition revealed that the thylakoid contained approximately 20% of the chloroplast PC. Our results demonstrate that lipids synthesized at the chloroplast surface as well as in the inner envelope membrane are transported to the thylakoid and that lipid sorting is involved in the process. Furthermore, the results also indicate that more than one pathway exists for galactolipid transfer from the chloroplast envelope to the thylakoid.     

Lipid-protein interactions in stacked and destacked thylakoid membranes and the influence of phosphorylation and illumination. Spin label ESR studies

The effects of membrane destacking, protein phosphorylation, and continuous illumination have been studied in pea thylakoid membranes using ESR spectroscopy of an incorporated spin-labelled phosphatidylglycerol. This spin-labelled analogue of an endogenous thylakoid lipid has previously been shown to exhibit a selectivity of interaction with thylakoid proteins. Neither destacking, phosphorylation nor illumination was found to change the ESR spectra appreciably, suggesting that for phosphatidylglycerol at least, neither the number of protein-associated membrane lipids nor their pattern of selectivity was altered. The redistribution of the thylakoid protein complexes in the membrane, under these various conditions, therefore takes place with conservation of the properties of the lipid/protein interface.     

Effects of Lipid Structure on the State of Aggregation of Potassium Channel KcsA

The state of aggregation of potassium channel KcsA was determined as a function of lipid:protein molar ratio in bilayer membranes of the zwitterionic lipid phosphatidylcholine (PC) and of the anionic lipid phosphatidylglycerol (PG). EPR (electron paramagnetic resonance) with spin-labeled phospholipids was used to determine the number of motionally restricted lipids per KcsA tetramer. Unexpectedly, this number decreased with a decreasing lipid:KcsA tetramer molar ratio in the range of 88:1 to 30:1, consistent with sharing of annular lipid shells and KcsA-KcsA contact at high mole fractions of protein. Fluorescence quenching experiments with brominated phospholipids showed a decrease in fluorescence quenching at low lipid:KcsA tetramer mole ratios, also consistent with KcsA-KcsA contact at high mole fractions of protein. The effects of low mole ratios of lipid seen in EPR and fluorescence quenching experiments were more marked in bilayers of PC than in bilayers of PG, suggesting stronger association of PG than PC with KcsA. This was confirmed by direct measurement of lipid association constants using spin-labeled phospholipids, showing higher association constants for all anionic lipids than for PC. The results show that the probability of contacts between KcsA tetramers will be very low at lipid:protein molar ratios that are typical of native biological membranes.     

Membrane insertion and lipid-protein interactions of bovine seminal plasma protein PDC-109 investigated by spin-label electron spin resonance spectroscopy

The interaction of the major acidic bovine seminal plasma protein, PDC-109, with dimyristoylphosphatidylcholine (DMPC) membranes has been investigated by spin-label electron spin resonance spectroscopy. Studies employing phosphatidylcholine spin labels, bearing the spin labels at different positions along the sn-2 acyl chain indicate that the protein penetrates into the hydrophobic interior of the membrane and interacts with the lipid acyl chains up to the 14th C atom. Binding of PDC-109 at high protein/lipid ratios (PDC-109:DMPC = 1:2, w/w) results in a considerable decrease in the chain segmental mobility of the lipid as seen by spin-label electron spin resonance spectroscopy. A further interesting new observation is that, at high concentrations, PDC-109 is capable of (partially) solubilizing DMPC bilayers. The selectivity of PDC-109 in its interaction with membrane lipids was investigated by using different spin-labeled phospholipid and steroid probes in the DMPC host membrane. These studies indicate that the protein exhibits highest selectivity for the choline phospholipids phosphatidylcholine and sphingomyelin under physiological conditions of pH and ionic strength. The selectivity for different lipids is in the following order: phosphatidylcholine approximately sphingomyelin > or = phosphatidic acid (pH 6.0) > phosphatidylglycerol approximately phosphatidylserine approximately and rostanol > phosphatidylethanolamine > or = N-acyl phosphatidylethanolamine > cholestane. Thus, the lipids bearing the phosphocholine moiety in the headgroup are clearly the lipids most strongly recognized by PDC-109. However, these studies demonstrate that this protein also recognizes other lipids such as phosphatidylglycerol and the sterol androstanol, albeit with somewhat reduced affinity.     

Protein-induced vertical lipid dislocation in a model membrane system: spin-label relaxation studies on avidin-biotinylphosphatidylethanolamine interactions.

The change in vertical location of spin-labeled N-biotinyl phosphatidylethanolamine in fluid-phase dimyristoyl phosphatidylcholine bilayer membranes, on binding avidin to the biotinyl headgroup, has been investigated by progressive saturation electron spin resonance measurements. Spin-labeled phospholipids were present at a concentration of 1 mol%, relative to total membrane lipids. For avidin-bound N-biotinyl phosphatidylethanolamine spin-labeled on the 8 C atom of the sn-2 chain, the relaxation enhancement induced by 30 mM Ni2+ ions confined to the aqueous phase was 2.5 times that induced by saturating molecular oxygen, which is preferentially concentrated in the hydrophobic core of the membrane. For phosphatidylcholine also spin-labeled at the 8 position of the sn-2 chain, this ratio was reversed: the relaxation enhancement by Ni2+ ions was half that induced by molecular oxygen. In the absence of avidin, the enhancement by either relaxant was the same for both spin-labeled phospholipids. For a double-labeled system, in which both N-biotinyl phosphatidylethanolamine and phosphatidylcholine were spin-labeled on the 12 C atom of the sn-2 chain, the relaxation rate in the absence of avidin was greater than that predicted from linear additivity of the corresponding singly labeled systems, because of mutual spin-spin interactions between the two labeled lipid species. On binding of avidin to the N-biotinyl phosphatidylethanolamine, this relaxation enhancement by mutual spin-spin interaction was very much decreased. These results indicate that, on binding of avidin to the lipid headgroup, N-biotinyl phosphatidylethanolamine is lifted vertically within the membrane, relative to the phosphatidylcholine host lipids. The specific binding of avidin to N-biotinyl phosphatidylethanolamine parallels the liftase activity proposed for activator proteins associated with the action of certain gangliosidases.     

ESR spin-label studies of lipid-protein interactions in membranes

Lipid spin labels have been used to study lipid-protein interactions in bovine and frog rod outer segment disc membranes, in (Na+, K+)-ATPase membranes from shark rectal gland, and in yeast cytochrome oxidase-dimyristoyl phosphatidylcholine complexes. These systems all display a two component ESR spectrum from 14-doxyl lipid spin-labels. One component corresponds to the normal fluid bilayer lipids. The second component has a greater degree of motional restriction and arises from lipids interacting with the protein. For the phosphatidylcholine spin label there are effectively 55 +/- 5 lipids/200,000-dalton cytochrome oxidase, 58 +/- 4 mol lipid/265,000 dalton (Na+, K+)-ATPase, and 24 +/- 3 and 22 +/- 2 mol lipid/37,000 dalton rhodopsin for the bovine and frog preparations, respectively. These values correlate roughly with the intramembrane protein perimeter and scale with the square root of the molecular weight of the protein. For cytochrome oxidase the motionally restricted component bears a fixed stoichiometry to the protein at high lipid:protein ratios, and is reduced at low lipid:protein ratios to an extent which can be quantitatively accounted for by random protein-protein contacts. Experiments with spin labels of different headgroups indicate a marked selectivity of cytochrome oxidase and the (Na+, K+)-ATPase for stearic acid and for cardiolipin, relative to phosphatidylcholine. The motionally restricted component from the cardiolipin spin label is 80% greater than from the phosphatidylcholine spin label for cytochrome oxidase (at lipid:protein = 90.1), and 160% greater for the (Na+, K+)-ATPase. The corresponding increases for the stearic acid label are 20% for cytochrome oxidase and 40% for (Na+, K+)-ATPase. The effective association constant for cardiolipin is approximately 4.5 times greater than for phosphatidylcholine, and that for stearic acid is 1.5 times greater, in both systems. Almost no specificity is found in the interaction of spin-labeled lipids (including cardiolipin) with rhodopsin in the rod outer segment disc membrane. The linewidths of the fluid spin-label component in bovine rod outer segment membranes are consistently higher than those in bilayers of the extracted membrane lipids and provide valuable information on the rate of exchange between the two lipid components, which is suggested to be in the range of 10(6)-10(7) s-1.     

Effects of lipolytic enzymes on the photochemical activities of spinach chloroplasts.

1. Spinach class II chloroplasts were treated with purified potato lipolytic acyl-hydrolase and venom phospholipase A2, and their lipid degradations and the effects on the photochemical activities were followed. 2. Potato lipolytic enzyme hydrolyzed monogalactosyldiacylglycerol at a faster rate than phospholipids such as phosphatidylglycerol and phosphatidylcholine. The treatment caused a rapid decrease of Photosystem I activity, and a less change of Photosystem II activity. 3. Venom phospholipase A2 which preferentially hydrolyzed phosphatidylglycerol, caused a rapid decrease of Photosystem II activity and only a slight decrease of photosystem I activity. 4. Potato enzyme and phospholipase A2 degraded the membrane lipids of glutaraldehyde-fixed chloroplasts at a rather slightly higher rate than those of non-treated chloroplasts. 5. The results suggested a possible correlation between monogalactosyldiacylglycerol degradation and decay of Photosystem I activity and between phosphatidylglycerol degradation and decay of Photosystem II activity. A possible mechanism is discussed.     

The action of lipases on chloroplast membranes. III. The effect of lipid hydrolysis on chlorophyll-protein complexes in thylakoid membranes

Bean thylakoid membranes treated with various lipolytic enzymes (bean galactolipase, phospholipases A₂, C, D) showed marked changes in their acyl lipid composition. As a consequence of acyl lipids hydrolysis, destruction of some chlorophyll a-protein complexes (CP1a, CP1, CPa) or monomerization of the oligomeric of light harvesting chlorophyll a/b protein complex (LHCP) was observed. It is concluded that galactolipids and phosphatidylcholine are responsible for the stability of CP1a, CP1 and CPa, respectively. Phosphatidylglycerol and to some extent monogalactosyldiacylglycerol are essential for the stabilization of oligomeric structures of light harvesting chlorophyll a/b protein complex.Abbreviations chl chlorophyll - CP1a, CP1 chl a-protein complexes, of PSI - CPa chl a-protein complex of PSII - DGDG diagalactosyldiacylglycerol - FC free chl - GL galactolipase - LHCP^1–3 light harvesting chl a/b protein complex - MGDG monogalactosyldiacylglycerol - PAGE polyacrylamide gel electrophoresis - PC phosphatidylcholine - PG phosphatidylglycerol - PLA₂ phospholipase A₂ - PL phospholipase C - PLD phospholipase D - PSI photosystem I - PSII photosystem II - SDS sodium dodecyl sulphate - SQDG sulfoquinovosyl-diacylglycerol - TCA trichloroacetic acid - Tricine N-tris-(hydroxymethyl)-methylglycine - Tris Tris-(hydroxymethyl)-aminomethan     

Effect of Temperature on Growth of Bacillus sp. T-4, a Thermophilic Acidophilic Bacterium

The lipid distribution and function in the thylakoid membranes from a thermophilic cyanobacterium, Mastigocladus laminosus, were investigated. The thylakoid membranes were treated with digitonin and separated on a DEAE-cellulose column into fractions enriched in photosystem I or II complex. Lipid analyses showed a specific distribution of anionic lipids among the fractions. A mild delipidation of the membranes with cholate indicates that monogalactosyl diacylglycerol (MGDG) and sulfoquinovosyl diacylglycerol (SQDG) are released rapidly, while the major parts of digalactosyl diacylglycerol (DGDG) and phosphatidylglycerol (PG) are tightly associated with membranes, suggesting a different distribution between the two groups of lipids. Measurements of fluorescence of delipidated and reconstituted thylakoids showed the contribution of lipids to energy transfer. MGDG enhanced all the original fluorescence of thylakoids, while acidic PG and SQDG stimulated fluorescence of photosystem I and antena chlorophyll-protein complexes. DGDG was less effective under the conditions tested.     

The role of lipids in photosystem II

The thylakoid membranes of photosynthetic organisms, which are the sites of oxygenic photosynthesis, are composed of monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG), and phosphatidylglycerol (PG). The identification of many genes involved in the biosynthesis of each lipid class over the past decade has allowed the generation and isolation of mutants of various photosynthetic organisms incapable of synthesizing specific lipids. Numerous studies using such mutants have revealed that deficiency of these lipids primarily affects the structure and function of photosystem II (PSII) but not of photosystem I (PSI). Recent X-ray crystallographic analyses of PSII and PSI complexes from Thermosynechococcus elongatus revealed the presence of 25 and 4 lipid molecules per PSII and PSI monomer, respectively, indicating the enrichment of lipids in PSII. Therefore, lipid molecules bound to PSII may play special roles in the assembly and functional regulation of the PSII complex. This review summarizes our present understanding of the biochemical and physiological roles of lipids in photosynthesis, with a special focus on PSII. This article is part of a Special Issue entitled: Photosystem II.     

Influence of the bovine seminal plasma protein PDC-109 on the physical state of membranes.

PDC-109 is the main component of bovine seminal plasma and has been suggested to play an important role in the genesis of bovine sperm cells. Here, the effect of binding of PDC-109 to membranes on the structure and physical properties of the lipid phase was investigated. For that, ESR measurements were undertaken on model membranes (lipid vesicles) and on biological membranes (epididymal spermatozoa) by employing various spin-labeled phospholipids. We found that PDC-109 alters the membrane structure of lipid vesicles as well as of bovine epididymal spermatozoa in that the mobility of spin-labeled phospholipids was reduced in the presence of the protein. This immobilizing effect of the protein was not restricted to analogues of phosphatidylcholine but was also detected with spin-labeled phosphatidylethanolamine. However, the extent of immobilization was lower for phosphatidylethanolamine compared with phosphatidylcholine, supporting the lipid headgroup specificity of the protein. Besides phospholipid headgroups, the physical state of membrane lipids is also important for the interaction of PDC-109 with membranes, in that, e.g., the immobilizing effect of the protein on labeled lipids was larger in membranes above the phase transition temperature compared with the effect below this temperature. The results are of relevance for understanding the physiological role of PDC-109 in the genesis of sperm cells.