Dipole Reversal in Bacteriorhodopsin and Separation of Dipole Components

Wang, Guangyu; Pörschke, Dietmar

doi:10.1021/jp027510v

Cited by 12 publications

(9 citation statements)

References 30 publications

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“…A recent investigation indicates that the overall dipole moment of the protein is compensated to a large extent, apparently by a nonsymmetric distribution of charges on lipid residues. 32 The overall permanent dipole moments obtained in the present investigation suggest that the change in the charge distribution between the resting and the M-state is negligible. However, a dipole change resulting from displacement of some residue(s) may be compensated by rearrangement of some other residue(s).…”

Section: Charge Distribution and Dipole Momentsupporting

confidence: 48%

“…A simple model calculation indicates the order of magnitude: motion of a proton from the intra-to the extra-cellular side may change the dipole moment by 1=2 £ e £ 50 £ 10 210 C m ¼ 120 D per protein molecule. This change is considerable with respect to the experimental dipole moment of , 50 D per monomer, but relatively small compared to the dipole moment calculated from the crystal structure of the protein in the order of 600 -800 D. 19,32 The effect of proton motion on the dipole moment may also be counterbalanced by motion of charged residues of the protein. A recent investigation indicates that the overall dipole moment of the protein is compensated to a large extent, apparently by a nonsymmetric distribution of charges on lipid residues.…”

Section: Charge Distribution and Dipole Momentmentioning

confidence: 78%

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Strong Bending of Purple Membranes in the M-state

Pörschke

2003

Journal of Molecular Biology

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Structure changes of purple membranes during the photocycle were analysed in solution by measurements of the electric dichroism. The D96N-mutant was used to characterize the M-state at neutral pH. The transition from the resting state to 61% photo-stationary M-state is associated with a strong reduction of the dichroism decay time constant by a factor of approximately 2. Because the change of the time constant is independent of the bacteriorhodopsin concentration, the effect is not attributed to light-induced dissociation but to light-induced bending of purple membranes. After termination of light-activation the dichroism decay of the resting state is restored with a time constant close to that of the M-state decay, which is more than two orders of magnitude slower than proton transfer to the bulk. Thus, bending is not due to asymmetric protonation but to the structure of the M-state. A very similar reduction of decay time constants at a corresponding degree of light-activation was found for wild-type bacteriorhodopsin at pH-values 7.8-9.3, where the lifetime of the M-state is extended. Light-induced bending is also reflected in changes of the stationary dichroism, whereas the overall permanent dipole moment remains almost constant, suggesting compensation of changes in molecular and global contributions. Bead model simulations indicate that disks of approximately 1 microm diameter are bent at a degree of photo-activation of 61% to a radius of approximately 0.25 microm, assuming a cylindrical bending modus. The large light-induced bending effect is consistent with light-induced opening of the protein on the cytoplasmic side of the membrane detected by electron crystallography, which is amplified due to coupling of monomers in the membrane. Bending may function as a mechanical signal.

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Section: Charge Distribution and Dipole Momentsupporting

confidence: 48%

Section: Charge Distribution and Dipole Momentmentioning

confidence: 78%

Strong Bending of Purple Membranes in the M-state

Pörschke

2003

Journal of Molecular Biology

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“…16a Although properties of the dipole in bR have not been well understood, the dipole moment of 3.3 Â 10 À28 C m per bR monomer 19 is believed to result from a charge asymmetry at the two sides of the bR-PM. 20 Such a dipole moment seems too small to have any noticeable impact on bulk materials; however, it is highly possible that it plays a critical role in nanoscale interactions, thus resulting in a significant effect on nanomaterials.…”

Section: Introductionmentioning

confidence: 99%

Bidirectional mediation of TiO2 nanowires field effect transistor by dipole moment from purple membrane

Song

et al. 2010

Nanoscale

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Bacteriorhodopsin-embedded purple membrane (bR-PM) is one of the most promising biomaterials for various bioelectronics applications. In this work, we demonstrate that a dipole bio-originated from bR-PM can bidirectionally mediate the performance of a bottom-contact TiO(2) nanowire field effect transistor (FET) for performance improvement. When negative gate voltage is applied, both transfer and output characteristics of the TiO(2) nanowire FET are enhanced by the bR-PM modification, resulting in a hole mobility increased by a factor of 2. The effect of the number of the deposited bR-PM layers on the normalized DeltaI(D) of the FET suggests that the additional electric field generated by the dipole moment natively existing in bR-PM actually boosts the performance of the TiO(2) nanowires FET.

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“…To demonstrate the power of the approach, we use the nanobioelectronic devices to extract information about the charge distribution in the particular membrane used, thereby contributing to the resolution of a long-standing question about charge distributions within that membrane. 6 The structure of the devices is illustrated in Figure 1. Patches of cell membrane covered a dense network of individual carbon nanotubes ( Figure 1A) contacted by metal electrodes, 8 referred to as a nanotube network field-effect transistor (NTN-FET).…”

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confidence: 99%

Integration of Cell Membranes and Nanotube Transistors

et al. 2005

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We report the integration of a complex biological system and a nanoelectronic device, demonstrating that both components retain their functionality while interacting with each other. As the biological system, we use the cell membrane of Halobacterium salinarum. As the nanoelectronic device, we use a nanotube network transistor, which incorporates many individual nanotubes in such a way that entire patches of cell membrane are contacted by nanotubes. We demonstrate that the biophysical properties of the membrane are preserved, that the nanoelectronic devices still function as transistors, and that the two systems interact. Further, we use the interaction to study the charge distribution in the biological system, finding that the electric dipole of the membrane protein bacteriorhodopsin is located 2/3 of the way from the extracellular to the cytoplasmic side.Nanobioelectronics, the integration of biological processes and molecules with nanoscale fabricated structures, offers the potential for electronic control and sensing of biological systems. 1 As a specific example, carbon nanotubes have been suggested for use as prosthetic nervous implants in organs such as eyes and ears. 2 To achieve this goal requires the parallel preparation 3 of fully functional biological systems and nanoelectronic systems that are integrated together. One major obstacle is the preservation of functionality in both systems. For example, while biological systems ranging from lipids 7 to living cells 2 have been assembled on nanotube substrates, the nanotubes have served only as mechanical supports, without electronic functionality. A second major obstacle is the difference in scale between nanostructures and biological systems. While nanotubes are comparable in size to individual proteins, they are much smaller than cells. Thus, nanotube electronic devices have been used as singlemolecule sensors 5a,7a rather than to communicate with complex biological systems. Here, we achieve integration between a functioning nanotube transistor and a cell membrane. We use nanotube networks, a recently developed class of nanotube devices, to bridge the gap in size between nanotechnology and biotechnology. To demonstrate the power of the approach, we use the nanobioelectronic devices to extract information about the charge distribution in the particular membrane used, thereby contributing to the resolution of a long-standing question about charge distributions within that membrane. 6

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Dipole Reversal in Bacteriorhodopsin and Separation of Dipole Components

Cited by 12 publications

References 30 publications

Strong Bending of Purple Membranes in the M-state

Strong Bending of Purple Membranes in the M-state

Bidirectional mediation of TiO2 nanowires field effect transistor by dipole moment from purple membrane

Integration of Cell Membranes and Nanotube Transistors

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