Improved model systems for bacterial membranes from differing species: Theimportance of varying composition in PE/PG/cardiolipin ternary mixtures

Figures & data

Figure 1. Steady-state fluorescence anisotropy, using TMA-DPH and DPH, and dynamic light scattering results showing the thermotropic lipid phase transitions of POPE:POPG:CL liposomes in HEPES buffer 10 mM, pH 7.4, 0.1 M NaCl, for two different lipid ratios.

Table I. Mean lipid transition temperatures (T_m/°C) obtained for the different lipid systems studied, using TMA-DPH and DPH steady-state fluorescence anisotropy, and by dynamic light scattering (DLS) methodology described by Michel et al. (2006). All lipid mixtures were studied in 10 mM HEPES buffer, pH 7.4, NaCl 0.1 M. The values represent the mean value of the five independent measures.

	POPE:POPG:CL (0.80:0.15:0.05)			POPE:POPG:CL (0.60:0.20:0.20)
	TMA-DPH	DPH	DLS	TMA-DPH	DPH	DLS
Tm(1)	19.2 ± 0.8	19.4 ± 1.1	20.2 ± 0.7	14.4 ± 1.2	13.2 ± 0.6	12.9 ± 1.1
Tm(2)	-----	-----	-----	42.0 ± 1.5	41.1 ± 1.3	40.6 ± 0.9

Table II. Different molecular species present in the cardiolipin mixture from E. coli extract.

Molecular species	Percentage of occurrence (%)	Transition Temperature (°C)	References
TMCL (14:0)	2.2	35.6–47.0	Nagamachi et al. (1985) Sankaram et al. (1989) Lewis et al. (2007)
tetrapentadecanoyl-cardiolipin (15:0)	4.8	47.0–56.0	-
TPCL (16:0)	33.3	56.0–62.2	Rainer et al. (1979) Nagamachi et al. (1985)
TPCL (16:1)	10.2	-	-
THCL (17:0)	1.4	58.0–61.0	Hubner et al. (1991) Rainer et al. (1979)
THCL (Cyclo 17:0)	27.0	-	-
TOCL (Trans 18:1)	14.4	< 0	Epand et al. (2009)
Tetranonadecanoyl-cardiolipin (19:0)	5.3	> 61.0	-

Figure 2. Atomic Force Microscopy image of bilayer produced from POPE:POPG:CL (0.80:0.15:0.05) liposomes, in HEPES buffer 10 mM, pH 7.4, 0.1 M NaCl at 26°C. The dashed line in the image (left) indicates the location of the height profile (right).

Table III. Comparison of the first transition temperature (T_m/°C) obtained for systems containing different POPE/POPG/CL proportions.

% lipids
POPE	POPG	CL	Tm (1)/°C
100	-	-	24.7^a/25.0^b
-	100	-	−2.0^b/ −5.32^a
-		100	<0 - 62^c
0.82	0.18	-	22.7^a
0.60	0.40	-	19.4^a/20.1^d
0.80	-	0.20	15.2^e
0.75	-	0.25	15.0^f
0.80	0.15	0.05	19.2^g
0.67	0.23	0.10	17.0^d
0.60	0.20	0.20	14.0^g

ªPozo Navas et al. (2005); ^bAvanti Polar Lipids (2010); ^c Lewis and McElhaney (2009); ^d Lopes et al. (2010); ^eDomènech et al. (2007); ^f Epand et al. (2007); ^gThis work.

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