Estimation of the permanent dipole moment of bacteriorhodopsin

Abstract

The static electric dipole moment persisting in bacteriorhodopsin was defined from electro-acoustic measurements of the dried films of purple membranes and compared with the value estimated from quantum chemical calculations. The projection of this value normal to the membrane surface is experimentally estimated to be equal to 40 D and oriented from the cytoplasmic side to the extracellular side of the membrane. This value is almost independent of the environment pH. QM/MM calculations were also performed for the known structures of the ground and intermediate states of bacteriorhodopsin. According to calculations the dipole moment is mainly determined by the cytoplasmic and extracellular coils, while the contribution from the transmembrane helices is smaller and of the opposite direction, and this value corresponding to the active centre is small. The calculated values of the dipole moment of bacteriorhodopsin in the intermediate states K, L, and M provide understanding about the origin of the driving force for the proton pumping. Employing the values of the dipole moments corresponding to the ground and intermediate states of bacteriorhodopsin, defined by means of QM/MM calculations, the experimentally determined photoelectric response of the dried films is explained.

Bacteriorhodopsin Enhances Efficiency of Perovskite Solar Cells

“…In the present model shown in Figure a, MAPbI 3 replaces the semiconductor quantum dot originally considered by King et al The FRET coupling strength U is determined by the relation where ε r is the permittivity of the medium, R is the separation between the molecules, D Pe and D bR are the dipole moments of the perovskite and bR, respectively, and the angular factor κ depends on the orientations of dipoles relative to R . We use the dipole values of D Pe = 1.94 D and D bR = 40 D based upon the literature. , We assume the medium dry and consider permittivity ε r = 1, κ = 1, and keep the bR/perovskite separation R as an independent variable. The model also needs another parameter γ, the inverse lifetime of a long-range exciton in bR, which has been determined to be around 0.05 eV according to King et al Other rates can be neglected as they are much smaller than γ.…”

“…We use the dipole values of D P e = 1.94 and D bR = 40 from literature. 19,20 We assume the medium dry and take a permittivity s r = 1, κ = 1 and keep the bR-perovsite separation distance R as a free parameter. The model also needs another parameter γ which is the inverse lifetime of an exciton in bR, and can be determined to be around 0.05 eV according to King et al 14 Other rates can be neglected in the calculations since they are much smaller than γ.…”

Mechanism of Proton Transfer in Bacteriorhodopsin

“…Mimicking photoinduced processes in bR is not a trivial task since the resulting outcome is sensitive to the amount of the protein environment, which has to be taken into account for calculations. For this purpose, Molecular Dynamics (MD) simulations have been intensively used previously [4,[27][28][29][30][31][32][33][34][35][36][37]. Indeed, the rotation of the Schiff base as a result of the retinal isomerization can be obtained by modeling the retinal with its protein environment [34,35].…”

Determination of the Surface Charge Density and Temperature Dependence of Purple Membrane by Electric Force Microscopy

“…11,12 By introducing external AC and DC electric fields, it has been reported that the permanent dipole moments (DMs) and induced DMs exist at low and high frequency of the applied electric field, respectively. 13,14 It was also suggested that the possible role of the DM is related to proton transport from the CP side to the EC side. 12 In a related experimental approach, electrostatic force microscopy (EFM) is another technique that can characterize the electrical properties of the biological membranes with nanometer resolution via probing the electrostatic force between the tip and sample.…”

“…As an important structural analytical technique, atomic force microscopy (AFM), working in liquid conditions has helped reveal the morphological difference between the two sides of PM. , The CP side was shown to display a hexagonal lattice of doughnut-shaped monomers with a repeat of 6.4 nm, while the EC side consisted of dot-like monomers with a repeat of 6.2 nm . This structural asymmetry of PM could result in the difference in the surface distribution of electric charges and dipoles because of the variation in the charged amino acid residues. , By introducing external AC and DC electric fields, it has been reported that the permanent dipole moments (DMs) and induced DMs exist at low and high frequency of the applied electric field, respectively. , It was also suggested that the possible role of the DM is related to proton transport from the CP side to the EC side . In a related experimental approach, electrostatic force microscopy (EFM) is another technique that can characterize the electrical properties of the biological membranes with nanometer resolution via probing the electrostatic force between the tip and sample .…”