Effects of Nonlamellar-prone Lipids on the ATPase Activity of SecA Bound to Model Membranes

Abstract

The effect of nonlamellar-prone lipids, diacylglycerol (DG) and phosphatidylethanolamine (PE), on the ATPase activity of SecA was examined. When Escherichia coli PE of the standard vesicles composed of 60 mol% of this lipid and 40 mol% of dioleoylphosphatidylglycerol (DOPG) is gradually replaced with either dioleoylglycerol (DOG) or dioeloyl PE (DOPE), the ATPase activity of SecA present together increased appreciably. On the other hand, when E. coli PE of the standard vesicles was replaced with DOG analogs, the SecA ATPase activity decreased slightly, and when replaced with phosphatidylcholine the decrease in the ATPase activity was more appreciable. When DOPE or E. coli PE was added to PC vesicles, the SecA ATPase activity was enhanced only slightly, suggesting that the hexagonal II structure per se is not important for the ATPase activity increase. It was observed that DOG induced phase separation of PG, and the lamellar-hexagonal II (L-HII) transition temperature of vesicles decreased by about 10 °C. The DOG analogs had no effect on these properties, suggesting the importance of the phase separation of PG and the decrease of L-HIItransition temperature of lipid bilayers to the SecA ATPase activity. The phase separation of PG by Ca2+ also brought about increased ATPase activity of SecA, underlining the importance of phase separation of PG for the enzyme activity. The incorporation of DOG or DOPE in the vesicle also increased the amount of SecA bound to model membranes and the extent of SecA penetration into the membrane. Studies with vesicles without SecA showed increased exposure of hydrophobic acyl chains when the DOG was present. Taken together, these observations suggest that the phase separation of PG and/or the bilayer penetration of SecA are mainly responsible for the enhanced SecA-vesicle interaction with concomitant increase in SecA ATPase activity. The effect of nonlamellar-prone lipids, diacylglycerol (DG) and phosphatidylethanolamine (PE), on the ATPase activity of SecA was examined. When Escherichia coli PE of the standard vesicles composed of 60 mol% of this lipid and 40 mol% of dioleoylphosphatidylglycerol (DOPG) is gradually replaced with either dioleoylglycerol (DOG) or dioeloyl PE (DOPE), the ATPase activity of SecA present together increased appreciably. On the other hand, when E. coli PE of the standard vesicles was replaced with DOG analogs, the SecA ATPase activity decreased slightly, and when replaced with phosphatidylcholine the decrease in the ATPase activity was more appreciable. When DOPE or E. coli PE was added to PC vesicles, the SecA ATPase activity was enhanced only slightly, suggesting that the hexagonal II structure per se is not important for the ATPase activity increase. It was observed that DOG induced phase separation of PG, and the lamellar-hexagonal II (L-HII) transition temperature of vesicles decreased by about 10 °C. The DOG analogs had no effect on these properties, suggesting the importance of the phase separation of PG and the decrease of L-HIItransition temperature of lipid bilayers to the SecA ATPase activity. The phase separation of PG by Ca2+ also brought about increased ATPase activity of SecA, underlining the importance of phase separation of PG for the enzyme activity. The incorporation of DOG or DOPE in the vesicle also increased the amount of SecA bound to model membranes and the extent of SecA penetration into the membrane. Studies with vesicles without SecA showed increased exposure of hydrophobic acyl chains when the DOG was present. Taken together, these observations suggest that the phase separation of PG and/or the bilayer penetration of SecA are mainly responsible for the enhanced SecA-vesicle interaction with concomitant increase in SecA ATPase activity. SecA is the central protein component of the translocation machinery for the newly synthesized proteins in Escherichia coli. This protein exists as a homodimer of a 102-kDa subunit and is distributed in vivo about equally between the inner membrane and cytosol (1Cabelli R.J. Dolan K.M. Qian L. Oliver D.B. J. Biol. Chem. 1991; 266: 24420-24427Abstract Full Text PDF PubMed Google Scholar). The protein translocation is brought about by a close cooperation between SecA, an ATPase, and other Sec proteins, such as SecB and SecY/E, and hydrolysis of ATP is required for this process (2Lill R. Cunningham K. Brundage L.A. Ito K. Oliver D. Wickner W. EMBO J. 1989; 8: 961-966Crossref PubMed Scopus (310) Google Scholar, 3Brundage L. Hendrick J.P. Schiebel E. Driessen A.J.M. Wickner W. Cell. 1990; 62: 649-657Abstract Full Text PDF PubMed Scopus (392) Google Scholar). SecA was also found to have another major function, an RNA helicase activity accompanying ATP hydrolysis, which may be necessary for the regulation of protein translocation (4Park S.K. Kim D.W. Choe J. Kim H. Biochem. Biophys. Res. Commun. 1997; 235: 593-597Crossref PubMed Scopus (25) Google Scholar). SecA binds to various phospholipid vesicles including those of phosphatidylcholine (PC). 1The abbreviations used are: PCphosphatidylcholinepyrenePE1-palmitoyl-2-(1-pyrenedecanoyl)-sn-glycero-3-phosphoethanolamineDGdiacylglycerolDOG1,2-dioleoyl-sn-glycerolpyS DHPEN-(1-pyrenesulfonyl)-1,2-dipalmitoyl-sn-glycero-3-phosphoethanolaminePEphosphatidylethanolamineDOPE1,2-dioleoyl-sn-glycero-3-phosphoethanolamineDOPG1,2-dioleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)]POPC1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholineNBD-PE1-palmitoyl-2-[12-[(7-nitro-2,1,3-benzodiazol-4-yl)amino]dodecanoyl]-sn-glycero-3-phosphoethanolamineNBD-PG1-palmitoyl-2-[12-[(7-nitro-2,1,3-benzodiazol-4-yl)amino]dodecanoyl]-sn-glycero-3-[phospho-rac-(1-glycerol)]THthe lamellar to hexagonal II phase transition temperaturePGphosphatidylglycerolL-HIIlamellar-hexagonal II. In solution, SecA has only a residual ATPase activity (5Lill R. Dowhan W. Wickner W. Cell. 1990; 60: 271-280Abstract Full Text PDF PubMed Scopus (465) Google Scholar). Although no discernible increase in this enzyme activity can be seen in the presence of PC vesicles, a tremendous enhancement of its activity is observed in the presence of vesicles, which has similar composition as the E. coli inner membrane, 60% phosphatidylethanolamine (PE) and 40% phosphatidylglycerol (PG) (5Lill R. Dowhan W. Wickner W. Cell. 1990; 60: 271-280Abstract Full Text PDF PubMed Scopus (465) Google Scholar). This differential effect of the vesicle composition seems to be related to the extent of binding and penetration of SecA to the vesicles. More SecA binds to vesicles containing E. coli lipids than those of PC (6Hendrick J.P. Wickner W. J. Biol. Chem. 1991; 266: 24596-24600Abstract Full Text PDF PubMed Google Scholar). SecA also penetrates deep into the lipid bilayer (7Ulbrandt N.D. London E. Oliver D.B. J. Biol. Chem. 1992; 267: 15184-15192Abstract Full Text PDF PubMed Google Scholar), and we have also found that SecA traverses the lipid bilayer (8Ahn T. Kim H. Biochem. Biophys. Res. Commun. 1994; 203: 326-330Crossref PubMed Scopus (25) Google Scholar, 9Ahn T. Kim H. J. Biol. Chem. 1996; 271: 12372-12379Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar). These observations suggest that the nonlamellar-prone lipid, PE, in the vesicles promotes the binding and penetration of SecA into the bilayer, which enhances the ATPase activity. In this connection, it is of interest that theE. coli membrane also contains another nonlamellar-prone lipid, diacylglycerol (DG), although the precise role of this lipid is not known. DG is a neutral lipid that can lower the lamellar to hexagonal II phase transition (L-HII) temperature (TH) of PE significantly (10Epand R.M. Biochemistry. 1985; 24: 7092-7095Crossref PubMed Google Scholar, 11Das S. Rand R.P. Biochemistry. 1986; 25: 2882-2889Crossref PubMed Scopus (205) Google Scholar). Even at low (2–3 mol%) concentrations, the DG stabilizes the HII structure of PE (11Das S. Rand R.P. Biochemistry. 1986; 25: 2882-2889Crossref PubMed Scopus (205) Google Scholar, 12Siegel D.P. Banschbach J. Yeagle P.L. Biochemistry. 1989; 28: 5010-5019Crossref Scopus (83) Google Scholar). In E. coli, DG accounts for about 1% of total membrane lipid, which depends on the growth conditions (13Raetz C.R.H. Newman K.F. J. Biol. Chem. 1978; 253: 3882-3887Abstract Full Text PDF PubMed Google Scholar). However, in some mutant strains, about 8% of DG is present in the inner membrane (14Raetz C.R.H. Newman K.F. J. Bacteriol. 1979; 137: 860-868Crossref PubMed Google Scholar). phosphatidylcholine 1-palmitoyl-2-(1-pyrenedecanoyl)-sn-glycero-3-phosphoethanolamine diacylglycerol 1,2-dioleoyl-sn-glycerol N-(1-pyrenesulfonyl)-1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine phosphatidylethanolamine 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine 1,2-dioleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine 1-palmitoyl-2-[12-[(7-nitro-2,1,3-benzodiazol-4-yl)amino]dodecanoyl]-sn-glycero-3-phosphoethanolamine 1-palmitoyl-2-[12-[(7-nitro-2,1,3-benzodiazol-4-yl)amino]dodecanoyl]-sn-glycero-3-[phospho-rac-(1-glycerol)] the lamellar to hexagonal II phase transition temperature phosphatidylglycerol lamellar-hexagonal II. The nonlamellar structure of membrane has been shown to play important roles in various cell functions. Several in vivo andin vitro studies indicated the involvement of nonlamellar structure of membrane in the translocation of secretory proteins across the plasma membrane (15Rietveld A.G. Koorengevel M.C. de Kruijff B. EMBO J. 1995; 14: 5506-5513Crossref PubMed Scopus (141) Google Scholar). Also, it was shown that nonlamellar lipid structure is induced by signal peptides (16Killian J.A. de Jong A.M. Ph. Bijvelt J. Verkleij A.J. de Kruijff B. EMBO J. 1990; 9: 815-819Crossref PubMed Scopus (89) Google Scholar). In particular, such activities as the ATP exchange by mitochondrial proteins (17Li L. Zheng L.X. Yang F.Y. Chem. Phys. Lipids. 1995; 76: 135-144Crossref PubMed Scopus (25) Google Scholar) and Ca2+-ATPase activity increase with increasing PE content (18Starling A.P. Dalton K.A. East J.M. Oliver S. Lee A.G. Biochem. J. 1996; 320: 309-314Crossref PubMed Scopus (38) Google Scholar), suggesting importance of nonlamellar structure. In the present investigation, the possible effect of nonlamellar structure of model membrane to the SecA-membrane interaction is examined by increasing the nonlamellar-prone lipids such as dioleoylglycerol (DOG) and dioleoylphosphatidylethanolamine (DOPE) in the lipid vesicles. For this, we gradually replaced the E. coli PE in liposomes initially consisting of 60% E. coli PE and 40% dioleoylphosphatidylglycerol (DOPG) with DOG or DOPE and measured the SecA ATPase activity (5Lill R. Dowhan W. Wickner W. Cell. 1990; 60: 271-280Abstract Full Text PDF PubMed Scopus (465) Google Scholar). DOPE has a lower lamellar to hexagonal II transition temperature (12 °C) than theE. coli PE (about 55 °C) and assumes the HIIconformation at room temperature. Our results show that the ATPase activity of SecA is able to recognize the nonlamellar structure of membrane and its ATPase activity increases with increasing nonlamellar-prone lipid content. However, the bulk of ATPase activity increase accompanying the enhanced SecA binding to the vesicles seems to come from the phase separation of PG present together. Phospholipids and DOG were purchased from Avanti Polar Lipids (Alabaster, AL) and were used without further purification. Fluorescence probes were from Molecular Probes. Chloroform solutions of lipids were stored in sealed ampules under argon at −20 °C. All other chemicals were of the highest grade commercially available. SecA protein was purified from a SecA-overproducing strain (RR1/pMAN400) (19Kawasaki H. Matsuyama S. Sasaki S. Akita M. Mizushima S. FEBS Lett. 1989; 242: 431-434Crossref PubMed Scopus (46) Google Scholar) as described (9Ahn T. Kim H. J. Biol. Chem. 1996; 271: 12372-12379Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar). The ATPase assay was performed in 100 μl of reaction buffer containing 100 mm NaCl, 1 mmdithiothreitol, 2 mm ATP, and 2 mmMgCl2. The sample solutions containing 1.5 μg of SecA protein and liposomes were incubated at 37 °C for 40 min prior to the analysis of the released inorganic phosphate (Pi) as described (20Lanzetta P.A. Alvarez L.J. Reinach P.S. Candia O.A. Anal. Biochem. 1979; 100: 95-97Crossref PubMed Scopus (1818) Google Scholar). The reactions were stopped by the addition of a color reagent (0.034% malachite green and 10.5 g/liter ammonium molybdate in 1 n HCl and 0.1% Triton X-100) and 100 μl of 34% citric acid solution. for min at room the was measured at of ATPase activity is as the hydrolysis of 1 of ATP per was by the as a standard Anal. Biochem. PubMed Scopus Google Scholar). of lipid composition coli E. coli coli were used these The of was at the 60 mol% of E. coli PE in the standard vesicles was by it with either mol% of 60 mol% of or 60 mol% of vesicles containing such as PE 2 mol% of these membrane probes were into For the of 1 mol% of 1-palmitoyl-2-[12-[(7-nitro-2,1,3-benzodiazol-4-yl)amino]dodecanoyl]-sn-glycero-3-phosphoethanolamine was the phase separation of lipids in the 10 mol% of or was into lipid an amount of lipids in to which was the was under a of argon The lipids were in a buffer mm containing 100 mm and/or 1 by and a in a for vesicles, the were and and membrane in an All vesicles used for this were for at 2 The in the measured with at this was than were by assay J. PubMed Scopus Google Scholar), and those of probes were at as the W. Chem. Phys. Lipids. PubMed Scopus Google Scholar). the the of into liposomes was measured as a of temperature at with the of K. P.A. D. Biochemistry. PubMed Scopus Google Scholar). The were with a PC with a The phase separation of lipids was at °C by the of and in the lipid bilayers at the and used for the of When the to of the was and was in the of The and were and 10 of in a was the of and effect by P.L. Biophys. J. 1985; Full Text PDF PubMed Scopus Google Scholar), the buffer was with argon for more than 2 the effect of nonlamellar-prone lipids on the binding of SecA to the model membrane, E. coli PE was replaced with DOG to mol% of total lipid or DOPE or PE to 1 of total PE The effect of phase separation of lipids on the SecA binding to model membranes was also by to liposomes containing 10 mol% or as a The amount of SecA bound to the membrane and the extent of its penetration into the bilayer were measured by from of SecA to (7Ulbrandt N.D. London E. Oliver D.B. J. Biol. Chem. 1992; 267: 15184-15192Abstract Full Text PDF PubMed Google Scholar) is at the of or is at the of at of 2 mol% of probes was into lipid of SecA and lipid vesicles be in the of were The reaction were incubated for 10 min at and the of at at or the at of was measured to the extent of the between the of and The used and the were the as in the phase transition and phase 1 that the ATPase activity of SecA increased with increasing of DOG in the vesicles by as as about when DOG content mol% of the lipid vesicle not 1 that the ATPase activity was enhanced by about when of the E. coli PE in the standard vesicles was replaced by DOPE in the of However, only a increase in the ATPase activity was seen when PE was used as the of DOG or This differential ATPase activity increase seems to be related to the with which the transition the of PE, and E. coli PE are and 55 H. J. Biochemistry. 1986; 25: PubMed Scopus Google Scholar). the effect of PE on the ATPase activity of SecA in the of PG, was 1 when the content of E. coli PE or DOPE in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine vesicles is the ATPase activity of SecA increased with a extent than the of standard vesicles containing DOPE showed a more effect on the activity than E. coli PE, which may from of these This that PE, a nonlamellar-prone lipid, is able to increase the ATPase activity of SecA only in the of Also, it be that vesicles containing which is in the HII at the temperature of 37 only a ATPase activity than the vesicles with E. coli PE, which is in the lamellar The effect of DOG analogs on the ATPase activity of SecA was also examined. 2 that the ATPase activity decreased with increasing vesicle of DG The DG analogs used are and The ATPase activity also decreased when E. coli PE in the standard vesicles was replaced by which is to be a lipid 2 It is that the of HII as as is for the increased ATPase activity of found that or of which a lamellar structure in the membrane, not protein translocation coli which PE when these lipids were into the inner DOPE are as of nonlamellar in various phospholipid we also the effect of DOG and its analogs on the transition temperature of vesicle that DOG decreased the of the standard vesicles by about 10 °C when mol% DOG was This with the incorporation of as as 1 mol% or the of is by °C R.M. Biochemistry. 1985; 24: 7092-7095Crossref PubMed Scopus Google Scholar, R.M. R. Biophys. PubMed Scopus Google Scholar, E. de de Kruijff B. Biochemistry. 1992; PubMed Scopus Google Scholar). The effect of DOG analogs on the was also and the results are shown in the of It is that the presence of these analogs in the vesicle not the It be that these analogs not the ATPase activity of are for the ATPase activity of SecA, and SecA binding and into model membranes (5Lill R. Dowhan W. Wickner W. Cell. 1990; 60: 271-280Abstract Full Text PDF PubMed Scopus (465) Google E. de de Kruijff B. Biochemistry. 1992; PubMed Scopus Google Scholar). It may be that the of is of the important the SecA ATPase activity and that this be by nonlamellar-prone this we the of the of J. J. Biochemistry. 1985; 24: PubMed Scopus Google Scholar) at °C. that the increased DOG in lipid bilayers brought about of the of liposomes containing 10 mol% of or as with the of the sample without This that DOG promotes the phospholipid in lipid bilayers the of with either PE or PG in the membrane. This also that the increase of the ATPase activity of SecA by nonlamellar-prone lipids from the of In we measured enzyme activity at 37 which is the phase transition temperature of liposomes In other liposomes are in the lamellar structure at this temperature. we may that the effect of nonlamellar-prone lipids on the ATPase activity of SecA is of the of lipid with However, we the that the of HII phase is important to the ATPase activity of SecA from the that the presence of E. coli PE in PC vesicles showed activity than the PC vesicle without PE 1 It is that the DOG analogs, which not an enhanced ATPase activity of SecA 2 also not the of either or and on the SecA ATPase the effect of phase separation of PG on the ATPase activity of SecA, we examined the of PG on the SecA ATPase activity. When was added to the standard liposomes coli PE, 40 mol% containing 10 mol% of the decreased as a of the of PG in the membrane also phase separation of PG in the vesicles containing 60 mol% DOPE or 60 mol% DOPE is the in the of PG and the effect on the phase Ca2+ the ATPase activity of SecA bound to the standard vesicles as as to the vesicles that 60 mol% of of the E. coli PE in the standard vesicles is an increase in the activity a 1 mm of the effect on the E. coli PE vesicles than that on the vesicles. These results that increase in the PG enhances the ATPase activity of These observations also suggest that the of of PG, of the presence of is in the regulation of the ATPase activity of SecA bound to The effect of nonlamellar-prone lipids and phase separation induced by Ca2+ on the binding of SecA to model membranes at °C was measured by the of of SecA by into the standard vesicles (7Ulbrandt N.D. London E. Oliver D.B. J. Biol. Chem. 1992; 267: 15184-15192Abstract Full Text PDF PubMed Google Scholar). that decreased with increasing of the increase in the SecA bound to model DOPE and PE also increased the of SecA bound to DOPE had a effect than PE as from It was that the increase in the lipid enhances the binding of SecA to vesicles as as its ATPase activity (5Lill R. Dowhan W. Wickner W. Cell. 1990; 60: 271-280Abstract Full Text PDF PubMed Scopus (465) Google Scholar). It is that the increased binding to vesicles containing DOG or than the of nonlamellar is responsible for the enhancement of ATPase activity. The decreased with increasing the enhanced SecA binding to lipid vesicles accompanying the phase When the that DOG and Ca2+ the phase separation of lipids in membranes is into this the that the of of the of SecA into the In other the of lipid with enhances the amount of SecA bound to lipid bilayers and increases the SecA ATPase activity. The effect of DOG on the of SecA into lipid bilayer was with between the of in SecA and PE at °C. The of and the of show the is to the of the at of PE, it is possible to the between these to the extent of SecA into lipid The extent of increased with increasing of DOG in the as shown by increasing of for at DOPE also increased the incorporation of SecA into the membrane was of the when PE was These results suggest that nonlamellar-prone lipids the of SecA into membrane. we measured the and of and in the membrane and the to the of The the of its in the membrane J.A. Biochemistry. 1985; 24: PubMed Scopus Google Scholar). The not when PE was replaced by nonlamellar-prone lipids not which was no of the probes in the presence of nonlamellar-prone possible in the membranes induced by we measured the of into the membrane, at at The decreased with increasing of DOG in the membrane the temperature This that DOG the exposure of acyl chains of lipids from the of the membrane to the However, the at DOG content at that the extent of exposure is similar at this temperature of the presence of this we used the by the between and into E. coli and PC vesicles, that the increased with increasing amount of DOG in the membrane at SecA is an protein that penetrates the lipid It only a ATPase activity in solution, the activity increases in the presence of vesicles containing In the presence of PC vesicles, is no enzyme activity other than the activity. In the present investigation, we observed that the DOG and which are to have a of nonlamellar when present in the vesicles with the lipid composition similar to theE. coli membrane, the ATPase activity of increase in activity by these nonlamellar-prone lipids was observed for a of and it was that the phase transition from lamellar to HII is responsible for the increase. this may not be the is in 1 which only a increase in ATPase activity or SecA binding when the content of E. coli PE its phase transition temperature or DOPE the transition temperature in PC vesicle is of such as enhancement of ATPase activity when phase separation in the standard vesicle was induced by suggest that the phase separation than phase transition is mainly responsible for the increased enzyme activity. It seems that the a nonlamellar-prone lipid, promotes phase although the precise of this is not The DOG analogs, which not phase also not the ATPase activity of In this connection, it is of interest that the of the protein for ATP, suggesting that the phase separation of protein activity T. E. M. T. T. T. E. K. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar). the we not have a for the increased ATPase activity of SecA accompanying phase separation of The results show that SecA binding and penetration into the membrane are enhanced by the phase This may that SecA penetration the PG and the increased ATPase activity is the of increased SecA that the membrane. The presence of DOG also induced the exposure of phospholipid acyl chains to the This may be the of the lamellar to HII the exposure may not be related to the phase The exposure the SecA binding to the vesicles. It was shown that the of SecA is than the of the SecA and that this is the the membrane T. E. M. T. T. T. E. K. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar). The penetration of the about its separation from the of The of the SecA contains the ATP binding and the ATPase activity is to be by the M. Kim H. J. Biochem. 1997; PubMed Scopus Google Scholar) when SecA assumes the structure. The of into the membrane this Taken together, the presence of nonlamellar-prone lipid promotes about phase separation of PG in promotes the of the of The of the effect of the by its membrane enhances the ATPase activity of the of membranes are in lipids that have to HII or nonlamellar membrane The importance of these lipids in membranes on the enzyme activities and protein has been for and mitochondrial (17Li L. Zheng L.X. Yang F.Y. Chem. Phys. Lipids. 1995; 76: 135-144Crossref PubMed Scopus (25) Google Scholar), Wickner W. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar), and Chem. Phys. Lipids. 1994; PubMed Scopus Google Scholar). Although these observations the important role of nonlamellar membrane in the enzyme activities or protein it is not phase separation is also in these In to the translocation of in E. coli, (15Rietveld A.G. Koorengevel M.C. de Kruijff B. EMBO J. 1995; 14: 5506-5513Crossref PubMed Scopus (141) Google Scholar) the for the role of nonlamellar-prone lipids to the of the cell membrane (15Rietveld A.G. Koorengevel M.C. de Kruijff B. EMBO J. 1995; 14: 5506-5513Crossref PubMed Scopus (141) Google Scholar). of the involvement of nonlamellar structure in the translocation is that signal peptides can the HII structure of membrane (16Killian J.A. de Jong A.M. Ph. Bijvelt J. Verkleij A.J. de Kruijff B. EMBO J. 1990; 9: 815-819Crossref PubMed Scopus (89) Google Scholar). However, the role of nonlamellar-prone lipids in the E. coli translocation has not been