PURPLE MEMBRANE: SURFACE CHARGE DENSITY and THE MULTIPLE EFFECT OF pH and CATIONS

Jonas, Roy E.; Koutalos, Yiannis; Tg, Ebrey

doi:10.1111/j.1751-1097.1990.tb08455.x

Cited by 94 publications

(84 citation statements)

References 79 publications

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“…Figures 4 and 5 show that D85 is predicted to be mostly deprotonated, which is consistent with the experimental pK a value of 2 obtained in high salt concentration. 70 In physiological pH range, our calculations show that the protonation probability of D85 varies slightly between 0.01 and 0.12 as a consequence of minor conformational variations between the structures ( Figure 5). This residue becomes fully deprotonated only at very high pH values, as shown by the contour line corresponding to a protonation probability of 0.01.…”

Section: Irregular Titration Curves and The Effect Of The Ph Gradientmentioning

confidence: 98%

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The Influence of a Transmembrane pH Gradient on Protonation Probabilities of Bacteriorhodopsin: The Structural Basis of the Back-Pressure Effect

Calimet

Ullmann

2004

Journal of Molecular Biology

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Bacteriorhodopsin pumps protons across a membrane using the energy of light. The proton pumping is inhibited when the transmembrane proton gradient that the protein generates becomes larger than four pH units. This phenomenon is known as the back-pressure effect. Here, we investigate the structural basis of this effect by predicting the influence of a transmembrane pH gradient on the titration behavior of bacteriorhodopsin. For this purpose we introduce a method that accounts for a pH gradient in protonation probability calculations. The method considers that in a transmembrane protein, which is exposed to two different aqueous phases, each titratable residue is accessible for protons from one side of the membrane depending on its hydrogen-bond pattern. This method is applied to several ground-state structures of bacteriorhodopsin, which residues already present complicated titration behaviors in the absence of a proton gradient. Our calculations show that a pH gradient across the membrane influences in a non-trivial manner the protonation probabilities of six titratable residues which are known to participate in the proton transfer: D85, D96, D115, E194, E204, and the Schiff base. The residues connected to one side of the membrane are influenced by the pH on the other side because of their long-range electrostatic interactions within the protein. In particular, D115 senses the pH at the cytoplasmic side of the membrane and transmits this information to D85 and the Schiff base. We propose that the strong electrostatic interactions found between D85, D115, and the Schiff base as well as the interplay of their respective protonation states under the influence of a transmembrane pH gradient are responsible for the back-pressure effect on bacteriorhodopsin.

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Section: Irregular Titration Curves and The Effect Of The Ph Gradientmentioning

confidence: 98%

“…The diagonal (broken line) represents a titration with DpH ¼ 0. The broken-line square shows the region delimited by the experimental pK a of D85 ðpK a , 2Þ 70 68,69 represent examples of sites which are always deprotonated (resp. protonated) over the whole pH ranges.…”

Section: Irregular Titration Curves and The Effect Of The Ph Gradientmentioning

confidence: 99%

The Influence of a Transmembrane pH Gradient on Protonation Probabilities of Bacteriorhodopsin: The Structural Basis of the Back-Pressure Effect

Calimet

Ullmann

2004

Journal of Molecular Biology

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“…While these observations are compatible with standard biophysical formalism, a surprising result was recorded when the protons were detected by an indicator that resides in the bulk. Pyranine (8-hydroxypyrene-l,3,6-trisulfonate) (~OH) does not adsorb to negatively charged purple membranes [9,10], thus its protonation measures how fast the acidic pulse propagates to the bulk. The rate of this reaction was measured by many research groups [3 8].…”

Section: Introductionmentioning

confidence: 99%

Quantitative evaluation of the dynamics of proton transfer from photoactivated bacteriorhodopsin to the bulk

Nachliel

Gutman

1996

FEBS Letters

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It has been reported by many research groups that protons released during the photocycle of bacteriorhodopsin are detected by surface bound indicators much faster than by indicators in the bulk. In this study we used numerical simulation of chemical reaction's dynamics for analyzing the delayed appearance of protons in the bulk. The results indicate that the low pK surface groups of the membrane, which form an undilutable concentrated matrix of proton binding sites, retain the protons in this space according to the mass action law. The main sites for proton accumulation are the cluster of carboxylates on the cytoplasmic side of the membrane. The protonation of an indicator in the bulk does not proceed by its reaction with free proton, but rather through self-diffusion of the indicator to the membrane and abstraction of proton from the protonated surface group. The detailed mechanisms which correspond with these reactions are reported.

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“…This is understandable, because changing the pH changes the protonation state of ionizable side groups within the protein. One needs to go to a pH of ϳ1.2 to change the ionized state of the phospholipid groups of the lipids (21,41).…”

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confidence: 99%

The Role of the Native Lipids and Lattice Structure in Bacteriorhodopsin Protein Conformation and Stability as Studied by Temperature-dependent Fourier Transform-Infrared Spectroscopy

Heyes

El‐Sayed

2002

Journal of Biological Chemistry

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We report the effect of partial delipidation and monomerization on the protein conformational changes of bacteriorhodopsin (bR) as a function of temperature. Removal of up to 75% of the lipids is known to have the lattice structure of the purple membrane, albeit as a smaller unit cell, whereas treatment by Triton monomerizes bR into micelles. The effects of these modifications on the protein secondary structure is analyzed by monitoring the protein amide I and amide II bands in the Fourier transform-infrared (FT-IR) spectra. It is found that removal of the first 75% of the lipids has only a slight effect on the secondary structure at physiological temperature, whereas monomerizing bR into micelles alters the secondary structure considerably. Upon heating, the bR monomer is found to have a very low thermal stability compared with the native bR with its melting point reduced from 97 to 65°C, and the premelting transition in which the protein changes conformation in native bR at 80°C could not be observed. Also, the N-H to N-D exchange of the amide II band is effectively complete at room temperature, suggesting that there are no hydrophobic regions that are protected from the aqueous medium, possibly explaining the low thermal stability of the monomer. On the other hand, 75% delipidated bR has its melting temperature close to that of the native bR and does have a pre-melting transition, although the pre-melting transition occurs at significantly higher temperature than that of the native bR (91°C compared with 80°C) and is still reversible. Furthermore, we have also observed that the reversibility of this pre-melting transition of both native and partially delipidated bR is time-dependent and becomes irreversible upon holding at 91°C between 10 and 30 min. These results are discussed in terms of the lipid and lattice contribution to the protein thermal stability of native bR.

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PURPLE MEMBRANE: SURFACE CHARGE DENSITY and THE MULTIPLE EFFECT OF pH and CATIONS

Cited by 94 publications

References 79 publications

The Influence of a Transmembrane pH Gradient on Protonation Probabilities of Bacteriorhodopsin: The Structural Basis of the Back-Pressure Effect

The Influence of a Transmembrane pH Gradient on Protonation Probabilities of Bacteriorhodopsin: The Structural Basis of the Back-Pressure Effect

Quantitative evaluation of the dynamics of proton transfer from photoactivated bacteriorhodopsin to the bulk

The Role of the Native Lipids and Lattice Structure in Bacteriorhodopsin Protein Conformation and Stability as Studied by Temperature-dependent Fourier Transform-Infrared Spectroscopy

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