Biochimica et Biophysica Acta 1788 (2009) 2101–2106 Contents lists available at ScienceDirect Biochimica et Biophysica Acta j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / b b a m e m The cardiolipin analogues of Archaea Angela Corcelli Dipartimento di Biochimica Medica, Biologia Medica e Fisica Medica, Università degli Studi di Bari, Piazza G. Cesare, 70124 Bari, Italy a r t i c l e i n f o Article history: Received 2 October 2008 Accepted 14 May 2009 Available online 20 May 2009 Keywords: Archaea Diphytanylglycerol diether lipids Extreme halophiles Dimeric phospholipids and phosphoglycolipids Osmotic stress a b s t r a c t The present article reviews studies of the structure and functional roles of the cardiolipin analogues of extremely halophilic prokaryotes belonging to the Archaea domain. Analogies and differences between the archaeal bisphosphatidylglycerol and the mitochondrial cardiolipin are presented. Furthermore the structure of archaeal glycophospholipid dimers is illustrated together with the available information on their function. The studies on the function of cardiolipin analogues in archaebacteria point out the tight interaction established by these phospholipids with membrane proteins and their role as bioactive lipids in the adaptation of microorganisms to osmotic stress. © 2009 Elsevier B.V. All rights reserved. 1. Introduction to the membrane biochemistry of Archaea Archaea are prokaryotes, which are able to colonize the most extreme environments on earth. Rift vents in deep sea, hot springs, extremely alkaline and acid waters, salt lake and coastal salterns represent typical environments where the Archaea flourish. The biochemistry of Archaea is quite different from other forms of life; one of the most peculiar aspects of the biochemistry of the third domain of phylogenetic tree is represented by the structures of cell membrane lipids. In contrast with Eukarya and Bacteria containing largely diacylglycerol-derived membrane lipids and some monoacyl-monoalkylglycerol-derived lipids, archaeal membrane lipids are unique in containing diphytanylglycerol diether lipids [1]. The saturated isopranoid hydrocarbon chains impart stability to peroxidation degradation and the ether linkages are resistant to chemical hydrolysis over a wide range of pH: these properties appear to be an advantage for microorganisms growing over a pH range of 5–10, exposed to air and sunlight at temperature even higher than 100 °C. The diether core lipid that forms the basis for most polar lipid structures present in archaeal microorganisms is 2,3-di-O-phytanylsn-glycerol (C20, C20), also called archaeol (Fig. 1). Therefore archaeal diether phospholipids contain the sn-glycerol-1-phosphate isomer (S configuration) and not the sn-glycerol-3-phosphate isomer, (R configuration) typically present in bacterial and eukaryal phospholipids; in other words archaeal phospholipids are the mirror images of the analogous diester glycerophospholipid found in all other organisms (Fig. 2). Information on lipid biosynthesis in Archaea is available thanks to labeling studies with whole cells [2,3]. E-mail address: a.corcelli@biologia.uniba.it. 0005-2736/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.bbamem.2009.05.010 Examples of phospholipid structures present in the archaeal microorganisms are archaeol analogues of phosphatidylglycerol, methyl ester of phosphatidylglycerophosphate, phosphatidylglycerosulfate and phosphatidic acid (Fig. 3). PA is normally detected only as minor components, probably because present as biosynthetic intermediates. While the chemical physical properties and aggregation states of membrane lipids of Bacteria and Eukarya are well known, the knowledge of the physical properties of archaeal lipids is relatively limited. However even from the limited knowledge of their properties and characteristics, it is clear that archaeal lipids are well adapted as membrane components in extreme environmental conditions. 2. The archaeal bisphosphatidylglycerol An interesting kind of phospholipid belonging to membranes of Bacteria and Eukarya is cardiolipin, or bisphosphatidylglycerol, a dimeric phospholipid constituted by phosphatidic acid linked to phosphatidylglycerol by a phosphoester bond having four chains in the hydrophobic tail. First evidence of the presence of cardiolipin analogues in the Archaea domain has been obtained in my laboratory. In collaboration with Morris Kates, we showed that the bisphosphatidylglycerol (archaeal BPG), sn-2,3-di-O-phytanyl-1-phosphoglycerol-3-phosphosn-di-O-phytanylglycerol is present in the extremely halophilic archaeon, Halobacterium salinarum [4]. Structure, proton NMR spectrum and the ESI-MS of the archaeal BPG are shown in Fig. 4a–c, respectively. The proton NMR spectrum (Fig. 4b) shows a group of resonances in the region 4.0–3.5 ppm arising from glycerol C-1, C-2 and C-3, while phytanyl chain CH3, CH2 and CH proton resonances are in the region 1.7–0.8 ppm. ESI-MS in Fig. 4c shows a monocharged molecular ion [M-H]− at m/z 1521.3 and a bischarged molecular ion [M-2H] 2− at m/z 760, in 2102 A. Corcelli / Biochimica et Biophysica Acta 1788 (2009) 2101–2106 Fig. 1. Chemical structure of 2,3-di-O-phytanyl-sn-glycerol (C20, C20), the basic unit of archaeabacterial phospholipids. good agreement with the molecular mass 1521.3 calculated for C89H182O13P2. The fragmentation ions at 731.7 and 805.9 correspond to PA and PG, which are compatible with a BPG structure. The archaeal bisphosphatidylglycerol, being a dimeric phospholipid, with a bridge structure and four chains in the hydrophobic tail, can be considered an analogue of eukaryal and bacterial cardiolipin. As the stereochemistry of archaeal and bacterial membrane lipids is different, it can be predicted that archaeal bisphosphatidylglycerol is in the S/S configuration, whereas bacterial or mitochondrial cardiolipin is in the R/R configuration. In both R/R and S/S configurations the two phosphate groups are not chemically equivalent. Two distinct 31P-NMR resonances have been reported for natural cardiolipin [5]; on the contrary in the case archaeal bisphosphatidylglycerol only one phosphorus resonance was detected by phosphorus NMR analysis [4,6]. Differently from NMR analyses of mitochondrial cardiolipin carried out at high concentrations [5], the available phosphorus NMR analyses of archaeal phospholipids have been performed with relatively low amount of lipid material, isolated and purified from lipid extracts of archaeons in culture with time consuming laboratory procedures [4,6]. Further parallel NMR studies on cardiolipin and archaeal BPG are required to clarify this discrepancy. The question arises if, as in the case of cardiolipin [7], the formation of a stable intramolecular hydrogen bond with the central hydroxyl group of the bridging glycerol is possible, determining a different level of acidity of the two phosphate residues in bisphopshatidylglycerol. Unfortunately data on pKa values of the two phosphate groups in the polar head of archaeal bisphosphatidylglycerol are not yet available. Information on the presence and distribution of bisphosphatidylglycerol among the halophilic Archaea, both in their natural habitat and in culture, was obtained by analyzing with electrospray ionization mass spectrometry the lipids extracted from the crystallizer ponds of two different salterns in the Mediterranean Sea (Margherita di Savoia in southern Italy and Eilat in Israel) and from cultures of various species of halophiles. Lipid analyses revealed the presence of the archaeal bisphosphatidylglycerol in the biomass of salterns, as well as in all species of archaeal halophiles examined [8]. In the various species of archaeal extreme halophilic microorganisms analyzed in our laboratory, it is invariably present the archaeal BPG carrying four identical C20 phytanyl chains; on the contrary many molecular species of bacterial and mitochondrial cardiolipin, deriving from difference in tail length, unsaturation and permutations of the four acyl chains, have been described [9]. One of the most important biochemical features of cardiolipin is its ability to tightly bind different protein complexes of the inner mitochondrial and bacterial membranes, which have bioenergetic functions. Although in last years considerable information accumulates in the literature on archaeal respiratory chains, very few data are available regarding the association of specific archaeal lipids with enzymes participating to oxidative phosphorylation and on the functional role of lipids in the bioenergetic functions of Archaea. It has been recently shown that membranes highly enriched in bisphosphatidylglycerol, isolated from an extremely halophilic archaeal microorganism Halorubrum sp., exhibit cytochrome c oxidase activity. Non denaturing gel electrophoresis revealed only one fraction having TMPD-oxidase activity in which archaeal BPG is the major lipid component. The cytochrome c oxidase activity of the archaeal BPG rich membranes was inhibited by the fluorescent dye 10-N-nonyl acridine orange (NAO) in a dose dependent manner (Fig. 5), indicating that bisphosphatidylglycerol is required for its functioning [10]. The tight association between cardiolipin and cytochrome c oxidase in mitochondria and bacteria is paralled in Archaea, attesting the universality of this specific lipid–protein interaction. Specific cardiolipins appear to be involved in the function of the respiratory chain complexes regardless of the phylogenetic background in which it occurs. The presence of dimeric phospholipids in Archaea can be considered as an example of convergent molecular evolution since in spite of the similarity of the lipid backbone, the chemical nature of the hydrophobic chain is distinct (fatty acids for bacteria and mitochondrion, phytanyl for Archaea) and consistent with the wide phylogenetic distance separating Bacteria from Archaea. Recently the possibility to specifically label archaeal bisphopshatidylglycerol with the fluorescent dye NAO in vivo has been examined. Both absorption and fluorescence spectroscopy studies have indicated that the interaction of archaeal bisphosphatidylglycerol with NAO is similar to that of cardiolipin. However, it has also been shown that other non dimeric phospholipids carrying two acid residues in the polar head and sulfoglycolipids present in the membrane of Archaea may mimic the interaction of mitochondrial cardiolipin with NAO [11]. These findings imply that it is not easy to explain NAO staining of archaebacteria, but also that NAO staining of bacterial species containing sulfoglycolipids should be interpreted with caution. 3. Dimeric archaeal glycophospholipids Hbt. salinarum can be considered as a model organism of archaeal world. One of the most interesting characteristics of Hbt. salinarum is represented by its ability to convert light in chemical energy for the metabolic requirements. This feature is due to the presence of a specialized membrane domain, containing the purple protein bacteriorhodopsin, a photoactivated proton pump, which sustains the ATP synthesis. One of the main lipid components in the lipid extract of the purple membrane of Hbt. salinarum is a complex phosphosulfoglycolipid, called in laboratory jargon glycocardiolipin or GlyC, (3-HSO3-Galp-β-1,6Manp-α-1,2-Glcp-α-1,1-[sn-2,3-di-O-phytanylglycerol]-6-[phospho-sn2,3-di-O-phytanylglycerol]. Having two diphytanylglycerol moieties (and four chains) in its molecule, the structure is analogous to that of cardiolipin. As said before, the purple membrane also contains minor amounts of archaeal BPG. Interestingly GlyC consists of a sulfo-triglycosyl diphytanylglycerol esterified to the phosphate group of phosphatidic acid; in addition NMR analysis shows that its polar head group is composed of the same sugars in the same sequence and anomeric configuration as in S-TGD-1, the major membrane glycolipid of Halobacterium, namely: Fig. 2. The different glycerol phosphate isomers used in the stereospecific biosynthesis of (a) archaeal and (b) bacterial and eukaryal phospholipids. A. Corcelli / Biochimica et Biophysica Acta 1788 (2009) 2101–2106 2103 Fig. 3. Phospholipids of archaeal microorganisms. (βGalp→αMan→αGlc) [4]. The sulfate group is also located on C-3 of the galactose residue, as in S-TGD-1 [12]. Therefore the novel phosphosulfoglycolipid has been named S-TGD1-PA (Fig. 6). Another archaeal glycosylated dimeric phospholipid was recently found in a membrane fraction isolated from an extreme halophilic archaeon, Halorubrum sp., isolated from the salt ponds in Margherita di Savoia, Italy [13]. By means of NMR and ESI-MS analyses it was shown that this cardiolipin analogue of Halorubrum also has the structure of a sulfo-glyco-diether-phosphatidic acid, i.e. a phospholipid dimer consisting of the glycolipid S-DGD-5 esterified to phosphatidic acid, namely S-DGD-5-PA, 2-HSO3-Manp-α-1,2-Glcp-α-1,1-[sn-2,3-di-Ophytanylglycerol]-6-[phospho-sn-2,3-di-O-phytanylglycerol] (see structure in Fig. 6). Again, NMR analysis shows that the sugars in the novel phospholipid are the same and in the same order as the glycolipid S-DGD-5 isolated from the Halorubrum membranes, in which the sulfatated mannose is linked to glucose[13]. Clearly the glycolipids S-TGD-1 and S-DGD-5 are precursor of S-TGD-1-PA and SDGD-5-PA, respectively [13,14]. Finally the glycosyl cardiolipin analogue S-GL-2, 6′-HSO3-D-Manp-α-1,2-D-Glcp-α-1,1-[sn-2,3-di-O-phytanylglycerol]-6-[phospho-sn-2,3-di-O-phytanylglycerol] was found in the membranes of Haloferax volcanii (Fig. 6) [15]. Dimeric phospholipids constituted by a glycolipid linked to phosphatidic acid have been previously found in pathogenic bacteria. Glycosylated cardiolipin was first detected in several strains of Streptococcus and identified as glucopyranosyl cardiolipin (Fig. 7) [16]. Later, in both the Gram-positive bacteria Lactococcus and Streptococcus, several complex glycolipids deriving from the kojibiosyl diacylglycerol structure were identified [17]. The function of these complex bacterial glycophospholipids has not yet been elucidated. 4. Functional roles: protein interactions and osmoadaptation Most information on the organization of archaeal lipids in the lipid bilayer, as well as on lipid–protein interactions, has been obtained from morphological, biophysical and biochemical studies on the specialized purple membrane patches of Hbt. salinarum [18–20]. The purple membrane contains the only protein bacteriorhodopsin and a small number of phospholipids and glycolipids. By electron microscopy and specific labeling, the glycolipids have been found exclusively in the outer leaflet of the membrane bilayer [21]. Localization of archaeal glycolipids in the purple membranes of Hbt. salinarum has also been achieved by in vivo labeling and neutron diffraction [22]. It has been suggested that the specific hydrophobic interactions between the tryptophan aromatic residues in the protein and carbohydrates in the lipids may play an important role in the stabilization and assembly of bacteriorhodopsin in the purple membrane [22]. It is not clear whether both glycolipids S-TGD-1 and S-TGD-1-PA interact directly with bacteriorhodopsin. The available biochemical data indicate that the interactions of bacteriorhodopsin with S-TGD-1-PA are stronger than those with S-TGD-1. It is extremely difficult to remove S-TGD-1-PA from the annulus of bacteriorhodopsin in the course of solubilization with detergents and even after lipid extraction with denaturing organic solvents a residual amount of S-TGD-1-PA still remains associated with denatured bacteriorhodopsin [23]. Furthermore the S-TGD-1-PA seems to play an important role in stability and maintaining the trimeric structure of bacteriorhodopsin [24]. The S-TGD-1-PA/bacteriorhodopsin stoichiometry in the purple membrane has been determined by analyzing an unprocessed lipid extract of the purple membrane with both of 31P-NMR and 1 H-NMR spectroscopy [6]. The molar ratio of S-TGD-1-PA to BR, in standard purple membrane preparation, is one and appears to be consistent with its possible location in the intra-trimer space [6]. Until now S-TGD-1-PA or glycocardiolipin has been found only in the extreme halophiles and in association with bacteriorhodopsin, while the archaeal bisphosphatidylglycerol is widespread in all genera of the family Halobacteriaceae [8]. 2104 A. Corcelli / Biochimica et Biophysica Acta 1788 (2009) 2101–2106 Fig. 4. Structure, NMR spectrum and ESI-MS profile of isolated and purified archaeal bisphosphatidylglycerol. Recently novel aspects regarding the regulation of the lipid biosynthesis in the archaeal extreme halophiles have been described [13,14]. When archaeal extreme halophiles are exposed to low salt conditions, relevant changes in the cell membrane lipid composition occur; during the adaptation of extreme halophilic microorganisms to hypo-osmolarity the membrane undergoes significant biochemical and structural changes, especially in terms of an increase in the content of cardiolipin analogues. Fig. 5. Inhibition of archaeal cytochrome c oxidase activity by NAO in bisphopshatidylglycerol rich membranes, isolated from an extreme halophilic microorganism. Oxidation kinetics of reduced horse heart cytochrome c (10 μM) by the archaeal membranes (protein concentration 9.4 μM). The reaction was followed at 550–540 nm; reported traces are the average of five independent experiments. As stated above, Hbt. salinarum cells possess a phospholipid dimer consisting of a glycolipid sulfo-triglycosyl-diether (S-TGD-1) esterified to the phosphatidic acid (PA), i.e. S-TGD-1-PA. S-TGD-1-PA is almost absent in the lipid extract of cells of Hbt. salinarum, while it is abundant in the purple membrane (PM), which is typically isolated after cell disruption by osmotic shock. It has been shown that osmotic stress specifically induces S-TGD-1-PA increase at the expenses of S-TGD-1 in Hbt. salinarum cells [14]. The membrane content of the archaeal cardiolipin analogue S-TGD-1-PA appears to be modulated by the extent of the incubation time and of osmotic unbalance across the membrane. Therefore, it is possible to isolate purple membrane at variable S-TGD-1-PA content to study the effect of subtle variation in the protein lipid annulus composition, avoiding the use of detergents and exogenous lipids [25]. Recently, osmotic shock has been also used as tool to modulate the cardiolipin content in native membrane of chromatophores of Rhodobacter sphaeroides [26]. Another example of the osmoregulated neosynthesis of phospholipid dimers in extremely halophilic Archaea has been described in an archaeon of the Halorubrum genus; membranes isolated after cell disruption by osmotic shock from Halorubrum sp. are highly enriched in archaeal bisphosphatidylglycerol (BPG) and reveal the presence of the cardiolipin analogue (or phospholipid dimmer) having the structure of a sulfodiglycosyl-diether-phosphatidic acid (S-DGD-5-PA). It has been clearly demonstrated that hyposmotic shock induces a specific increase in the content of archaeal BPG and S-DGD-5-PA in Halorubrum sp., at the expense of phosphatidylglycerol and the glycolipid SDGD-5, respectively [13]. Fig. 8 illustrates the conversion of PG in BPG in Halorubrum sp cells under osmotic shock. The evidence that osmotic shock stimulates the de novo synthesis of phospholipid dimers, i.e. cardiolipin analogues, in extreme halophilic Archaea, together with similar literature reports on bacterial organisms [for A. Corcelli / Biochimica et Biophysica Acta 1788 (2009) 2101–2106 2105 Fig. 6. Dimeric glycophospholipids of extremely halophilic archeons. example as in refs 26–30], suggests a general role for “cardiolipin” in osmoadaptation. A higher archaeal cardiolipin cell content could protect the cell from lysis. The increase in archaeal cardiolipin occurring in cells undergoing osmotic shock may represent the physiological response of the extremely halophilic archaeal microorganisms to the dilution of the salt saturated water occurring during rainfalls. The modifications in lipid composition could affect the physical–chemical properties of the membrane, such as bilayer thickness, membrane fluidity and transport properties. Much remains to be learned concerning the precise asymmetric arrangement of the archaeal cardiolipins in the membrane bilayer, the precise mode of interaction of the cardiolipins with the membrane proteins, the transmembrane distribution with respect to ion transport, permeability to nutrients, proton transport and conductance, and energy transduction. Fig. 7. Structure of a bacterial dimeric glycophospholipid. Fig. 8. Conversion of phosphatidylglycerol (PG) in bisphosphatidylglycerol (BPG) in an extremely halophilic archeon under osmotic stress. 2106 A. Corcelli / Biochimica et Biophysica Acta 1788 (2009) 2101–2106 Acknowledgements With the financial support of MIUR (Minister of School, University and Research) and the Italian Minister of Defense. References [1] M. Kates, Membrane lipids of Archaea, in: M. Kates, D.J. Kushner, A.T. Matheson (Eds.), The Biochemistry of Archaea (Archaebacteria), Elsevier, Amsterdam, 1993, pp. 261–295. [2] M. Kates, M.K. Wassef, D.J. Kushner, Radioisotopic studies on the biosynthesis of the glyceryl diether lipids of Halobacterium cutirubrum, Can. J. Biochem. 46 (1968) 971–977. [3] Y. Boucher, M. Kamekura, W.F. Doolittle, Origins and evolution of isoprenoid lipid biosynthesis in archaea, Mol. Microbiol. 52 (2) (2004) 515–527. [4] A. Corcelli, M. Colella, G. Mascolo, F.P. Fanizzi, M. Kates, A novel glycolipid and phospholipid in the purple membrane, Biochemistry 39 (2000) 3318–3326. [5] G.L. Powell, J. Jacobus, Nonequivalence of the phosphorus atoms in cardiolipin, Biochemistry 13 (1974) 4024–4026. [6] A. Corcelli, V.M.T. Lattanzio, P. Papadia, F.P. Fanizzi, Lipid/protein stoichiometries in a crystalline biological membrane: NMR quantitative analysis of the lipid extract of the purple membrane, J. Lipid Res. 43 (1) (2002) 132–140. [7] M. Kates, J.Y. Syz, D. Gosser, T.H. Haines, pH-dissociation characteristics of cardiolipin and its 2′-deoxy analogue, Lipids 28 (1993) 877–882. [8] V.M.T. Lattanzio, A. Corcelli, G. Mascolo, A. Oren, Presence of two novel cardiolipins in the halophilic archaeal community in the crystallizer brines from the salterns of Margherita di Savoia (Italy) and Eilat (Israel), Extremophiles 6 (2002) 437–444. [9] M. Schlame, M. Ren, Y. Xu, M.L. Greenberg, I. Haller, Molecular symmetry in mitochondrial cardiolipin, Chem. Phys. Lipids 138 (2005) 38–49. [10] A. Corcelli, S. Lobasso, L.L. Palese, M. Sublimi Saponetti, S. Papa, Cardiolipin is associated with the terminal oxidase of an extremely halophilic archaeon, BBRC 354 (2007) 795–801. [11] S. Lobasso, M. Sublimi Saponetti, F. Polidoro, P. Lopalco, J. Urbanija, V. Kralj-Iglic, A. Corcelli, Archaebacterial lipid membranes as models to study the interaction of 10n-nonyl acridine orange with phospholipids, Chem. Phys. Lipids 157 (2009) 12–20. [12] M. Kates, P.W. Deroo, Structure determination of the glycolipid sulfate from the extreme halophile Halobacterium cutirubrum, J. Lipid Res. 14 (1973) 438–445. [13] P. Lopalco, S. Lobasso, F. Babudri, A. Corcelli, Osmotic shock stimulates de novo synthesis of two cardiolipins in an extreme halophilic archaeon, J. Lipid Res. 45 (2004) 194–201. [14] S. Lobasso, P. Lopalco, V.M.T. Lattanzio, A. Corcelli, Osmotic shock induces the presence of glycocardiolipin in the purple membrane of Halobacterium salinarum, J. Lipid Res. 44 (2003) 2120–2126. [15] G.D. Sprott, S. Laroque, N. Cadotte, C.J. Dicaire, M. McGee, J.I. Brisson, Novel polar lipids of halophilic eubacterium Planococcus H8 and archaeon Haloferax volcanii, Biochim. Biophys. Acta 1633 (2003) 179–188. [16] W. Fischer, The polar lipids of group B Streptococci. I. Glucosylated diphosphatidylglycerol, a novel glycophospholipid, Biochim. Biophys. Acta 487 (1) (1977) 74–88. [17] W.M. O'Leary, S.G. Wilkinson, Gram positive bacteria, Chapter 5, in: C. Ratledge, C. May, et al., (Eds.), Microbial Lipids, 1, Acad Press, 1988, pp. 117–201. [18] D. Oesterhelt, W. Stoeckenius, Isolation of cell membrane of Halobacterium halobium and its fractionation into red and purple membrane, Methods Enzymol. 31 (1974) 667–678. [19] N. Grigorieff, T.A. Ceska, K.H. Dowing, J.M. Baldwin, R. Henderson, Electroncrystallographic refinement of the structure of bacteriorhodopsin, J. Mol. Biol. 259 (1996) 393–421. [20] M.P. Krebs, T.A. Isenbarger, Structural determinants of purple membrane assembly, Biochem. Biophys. Acta 1460 (2000) 15–26. [21] R. Henderson, J.S. Jubb, S. Whytock, Specific labelling on the protein and lipid on the extracellular surface of purple membrane, J. Mol. Biol. 123 (1978) 259–274. [22] M. Weik, H. Patzelt, G. Zaccai, D. Oesterhelt, Localization of glycolipids in membrane by in vivo labeling and neutronal diffraction, Mol. Cell 1 (1998) 411–419. [23] L. Catucci, V.M.T. Lattanzio, S. Lobasso, A. Agostiano, A. Corcelli, Role of endogenous lipids in the chromophore regeneration of bacteriorhodopsin, Bioelectrochemistry 63 (2004) 111–115. [24] F. Lopez, S. Lobasso, M. Colella, A. Agostano, A. Corcelli, Light-dependent and biochemical properties of two different bands of bacteriorhodopsin isolated on phenyl-sepharose CL-4B, Photochem. Photobiol. 69 (1999) 599–604. [25] A. Corcelli, S. Lobasso, M. Sublimi Saponetti, A. Leopold, N.A. Dencher, Glycocardiolipin modulates the surface interaction of the proton pumped by bacteriorhodopsin in purple membrane preparations, BBA-Biomembranes (2007) 2157–2163. [26] V. De Leo, L. Catucci, A. Ventrella, F. Milano, A. Agostiano, A. Corcelli, Cardiolipin increases in chromatophores isolated from Rhodobacter sphaeroides after osmotic stress: structural and functional roles, J. Lipid Res. 50 (2) (2009) 256–264. [27] A. Okabe, Y. Hirai, H. Hayashi, Y. Kanemasa, Alteration in phospholipid composition of Staphilococcus aureus during formation of autoplast, Biochim. Biophys. Acta 617 (1) (1980) 28–35. [28] L. Catucci, N. Depalo, V. Lattanzio, A. Agostiano, A. Corcelli, Neo-synthesis of cardiolipin in Rhodobacter sphaeroides under osmotic stress, Biochemistry 43 (47) (2004) 15066–15072. [29] T. Romantsov, S. Helbig, D.E. Culham, C. Gill, L. Stalker, J.M. Wood, Cardiolipin promotes polar localization of osmosensory transporter ProP in E. coli, Mol. Microbiol. 64 (6) (2007) 1455–1465. [30] E. Mileykovskaya, Subcellular localization of Escherichia coli osmosensor transporter ProP: focus on cardiolipin membrane domains, Mol. Microbiol. 64 (6) (2007) 1419–1422.
© Copyright 2024 Paperzz