A calorimetric study of white and purple membranes

Maglova, L.; Guleva, D.; Chekulaeva, L. N.; Атанасов, Б.

doi:10.1016/0005-2728(90)90187-9

Cited by 4 publications

(2 citation statements)

References 22 publications

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“…bleached and the reduced membranes these conformational A recent similar result has been reported by Maglova et al changes start between 60-70°C (Fig. 3), and extent to the [35] with the white mutant. The phosphate influence in the experimental limit (95°C).…”

Section: Ftir Measurementssupporting

confidence: 85%

The role of retinal in the thermal stability of the purple membrane

Cladera

Galisteo²,

Sabés

et al. 1992

European Journal of Biochemistry

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Differential scanning calorimetry demonstrates that the bleached form of the purple membrane does not possess any measurable thermal transition in water, up to 105"C, whereas in 0.1 M phosphate pH 7.5 it shows a transition at about 8 2 T , with an enthalpy of 110 kJ/mol. In the latter medium, the native membrane shows the main transition at 97"C, with an enthalpy of 390 kJ/mol. The reduced form of the purple membrane shows two small transitions in water, as well as in 0.1 M phosphate, which do not seem to be related to the main thermal transition of the native membrane. Fouriertransform infrared spectra in D 2 0 show that the two modified samples, as well as the native one, undergo similar secondary structural changes upon thermal denaturation. These changes appear to extend through a wide temperature range for both modified forms, particularly for the bleached one. The results suggest that the main thermal transition in the purple membrane is due to a cooperative conformational change involving the disruption of the network of electrostatic and hydrogen-bonding interactions which originate from the protonated Schiff base. In the two modified membranes, these conformational changes appear to proceed smoothly through a rather low or non-cooperative process. The thermal behaviour of the bleached membrane in water resembles that of the molten globule state described for several globular proteins.Bacteriorhodopsin is a retinylidene protein found in the purple membrane patches of Halobacterium halobium cells. It translocates protons from the inside to the outside of the cell upon light absorption, thus forming a proton gradient across the celular membrane. The protein is arranged in seven transmembrane a-helices, and possess a retinal molecule attached to a lysine residue through a protonated Schiff base [I -31. The bacteriorhodopsin molecules are distributed through the bilayer in trimers, which in turn are ordered in a two-dimensional hexagonal array. Thermal denaturation studies of bacteriorhodopsin have shown the high stability of the purple complex. At neutral pH, the melting temperature (t,,,) is found near 95°C for the major transition of the native complex, which is found to be an irreversible process [4]. Extreme pH values [5], deionization [6], delipidation [7], or incorporation of bacteriorhodopsin in vesicles [8] lowers the t,, but in all cases the enthalpy of denaturation is about four times lower than those found for globular proteins [9]. This lower denaturation enthalpy seems to be the general situation for all the intrinsic membrane proteins so far investigated, a fact related to the lack of protein/water interactions in their denatured state [lo].The thermal transition is accompanied by decoloration due to the hydrolysis of the retinal Schiff base. On the other hand, it is known that the retinal molecule occupies a central position in the seven a-helical rods [l 11 and thus it can act as a tightening or clamping element. These features prompted us to investigate the influence of the retinal molecule...

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Section: Ftir Measurementssupporting

confidence: 85%

The role of retinal in the thermal stability of the purple membrane

Cladera

Galisteo²,

Sabés

et al. 1992

European Journal of Biochemistry

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“…Similar results have been reported for the lipids extracted from Halobacterium cutirubrum (Chen et al, 1974). Note also that no thermal transition was detected in the purple membrane over the same temperature range by differential scanning calorimetry (Magbova et al, 1990; B. PiknovQ, unpublished results). As already mentioned, there are approximately 7 -8 polar lipid moleculeshacteriorhodopsin molecule in the purple membrane (Bakker and Caplan, 1978;Kates et al, 1982).…”

Section: Fluorescence Polarization Experimentsmentioning

confidence: 88%

Hydrophobic mismatch and long‐range protein/lipid interactions in bacteriorhodopsin/phosphatidylcholine vesicles

Piknová

Perochon

Tocanne

1993

European Journal of Biochemistry

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Mismatch between the hydrophobic thicknesses of transmembrane proteins and the supporting lipid bilayer and its consequences on the lateral organization of lipids have been investigated with bacteriorhodopsin and phosphatidylcholine species with a variety of acyl-chain lengths. The purple membrane, from the bacterium Halobacteriuin halobium, was used and reconstituted with dilauroyl-(Lau,GroPCho), dimyristoyl-(Myr,GroPCho), dipalmitoyl-(Pam,GroPCho) and distearoyl-(Ste, GroPCho) glycerophosphocholine. The phase behaviour of the lipids was investigated at different temperatures and different protein/lipid molar ratios, by analyzing the fluorescence excitation spectra of the 1 -acyl-2-[ 8-(2-anthroyl)-octanoyl]-sn-glycero-3-phosphocholine probe, and by measuring the fluorescence depolarization of the 1,6-diphenyl-l,3,5-hexatriene probe. Data obtained with 1 -acyl-2-[8-(2-anthroyl)-oct~oyl]-sn-glycero-3-phosphocholine shows that bacteriorhodopsin produced positive or negative shifts in the phase transition temperature of the host lipids depending on the strength and sign of the mismatch between the lipid and protein hydrophobic thicknesses and also on the protein concentration and aggregation state in the lipid bilayer. In the region of high protein concentration (bacteriorhodopsidphosphatidylcholine molar ratios = 1 : 50) and despite the presence of the endogenous lipids, bacteriorhodopsin (hydrophobic length d, = 3.0 -3.1 nm) brought about a large upward shift in the phase-transition temperature of Lau,GroPCho (AT = 40 K, mean hydrophobic thickness d = 2.4 nm), and to a lesser extent of Myr,GroPCho (AT = 23 K, d = 2.8 nm), accounting for a strong rigidifying effect of the protein on these short-chain lipids. Bacteriorhodopsin had no influence on the phase properties of Pam,GroPCho (AT = 0 K, d 3.2 nm), a lipid whose mean hydrophobic thickness is similar to that of the protein. In contrast, the transition temperature of Ste,GroPCho was decreased (AT = -13 K, d = 3.7 nm), indicating a fluidifying effect of the protein on this long-chain lipid. Similar effects on the lipid acyl-chain order were observed in the region of high-protein dilution (bacteriorhodopsidphosphatidylcholine molar ratios < 1 : 500).In this region and for Lau,GroPCho, both the spectroscopic data and circular-dichroism spectra indicated that the protein was in the monomeric form. Phase diagrams, in temperature versus bacteriorhodopsin concentration, were constructed for Lau,GroPCho and Ste,GroPCho. On account of microscopic theoretical models and of the relative values of d, and d, these diagrams indicate a preference of the protein for those lipid molecules which are in the gel-ordered state in Lau2. GroPCho but in the liquid disordered state in Ste,GroPCho. The phase diagram of Lau,GroPCho was also analyzed using another theoretical approach based upon elastic models within the Landaude Gennes theory. This allowed for the estimation of the coherence length < which characterizes the distance over which the hydrophobic thickness of the lipid bilay...

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Kinetic study into the irreversible thermal denaturation of bacteriorhodopsin

Galisteo

Sánchez‐Ruiz

1993

Eur Biophys J

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A calorimetric study of white and purple membranes

Cited by 4 publications

References 22 publications

The role of retinal in the thermal stability of the purple membrane

The role of retinal in the thermal stability of the purple membrane

Hydrophobic mismatch and long‐range protein/lipid interactions in bacteriorhodopsin/phosphatidylcholine vesicles

Kinetic study into the irreversible thermal denaturation of bacteriorhodopsin

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