Biomedical subjects

D Oesterhelt

Publications and source records attributed to D Oesterhelt.

At least 19 recordsLinked to original sources

PubMed2002

Proton translocation by bacteriorhodopsin in the absence of substantial conformational changes.

Unlike wild-type bacteriorhodopsin (BR), the BR triple mutant D96G/F171C/F219L has been shown to undergo only minor structural rearrangements during its photocycle. Nonetheless, the mutant is capable of transporting protons at a rate of 125(+/-40) H+/BR per minute under light-saturating conditions. Light adaptation of the triple mutant's retinal proceeds in a pH-dependent manner up to a maximum of 63% all-trans. These two findings imply that the transport activity of the triple mutant comprises 66% of the wild-type activity. Time-resolved spectroscopy reveals that the identity and sequence of intermediates in the photocycle of the triple mutant in the all-trans configuration correspond to that of wild-type BR. The only differences relate to a slower rise and decay of the M and O intermediates, and a significant spectral contribution from a 13-cis component. No indication for accumulation of the N intermediate is found under a variety of conditions that normally favor the formation of this species in wild-type BR. The Fourier transform infrared (FTIR) spectrum of the M intermediate in the triple mutant resembles that of wild type. Minor changes in the amide I region during the photocycle suggest that only small movements of the protein backbone occur. Electron microscopy reveals large differences in conformation between the unilluminated state of the mutant protein and wild-type but no light-induced changes in time-resolved measurements. Evidently, proton transport by the triple mutant does not require the major conformational rearrangements that occur on the same time-scale with wild-type. Thus, we conclude that large conformational changes observed in the photocycle of the wild-type and many BR mutants are not a prerequisite for the change in accessibility of the Schiff base nitrogen atom that must occur during vectorial catalysis to allow proton transport.

Archaea↗

PubMed2002

Kinetics, energetics, and electronic coupling of the primary electron transfer reactions in mutated reaction centers of Blastochloris viridis.

Femtosecond spectroscopy in combination with site-directed mutagenesis has been used to study the dynamics of primary electron transfer in native and 12 mutated reaction centers of Blastochloris (B) (formerly called Rhodopseudomonas) viridis. The decay times of the first excited state P* vary at room temperature between of 0.6 and 50 ps, and at low temperatures between 0.25 and 90 ps. These changes in time constants are discussed within the scope of nonadiabatic electron transfer theory using different models: 1) If the mutation is assumed to predominantly influence the energetics of the primary electron transfer intermediates, the analysis of the room temperature data for the first electron transfer step to the intermediate P(+)B(A)(-) yields a reorganization energy lambda = 600 +/- 200 cm(-1) and a free energy gap Delta G ranging from -600 cm(-1) to 800 cm(-1). However, this analysis fails to describe the temperature dependence of the reaction rates. 2) A more realistic description of the temperature dependence of the primary electron transfer requires different values for the energetics and specific variations of the electronic coupling upon mutation. Apparently the mutations also lead to pronounced changes in the electronic coupling, which may even dominate the change in the reaction rate. One main message of the paper is that a simple relationship between mutation and a change in one reaction parameter cannot be given and that at the very least the electronic coupling is changed upon mutation.

Alphaproteobacteria↗

PubMed2001

Photoresponsive dendritic azobenzene peptides.

Two dendritic peptides containing a branched lysine core and up to eight azobenzene moieties in the periphery were synthesized on solid support employing the omega-amino acid 4-(aminomethyl)phenylazobenzoic acid. With an additional peptidic tail consisting of an oligolysine portion, water solubility was achieved for the dendrimers, which allowed for the characterization of the cis/trans photoisomerization of the dendritic azobenzene species in both organic and aqueous media. Despite the interactions between the chromophores, which occur particularly in aqueous media, at higher dilution the photoisomerization process was found to proceed to extents that should permit photomodulation of molecular recognition processes between ligands grafted to the photosensitive azobenzene units and receptor molecules.

Azo Compounds↗

PubMed2001

Dynamics of the proton transfer reaction on the cytoplasmic surface of bacteriorhodopsin.

The cytoplasmic surface of bacteriorhodopsin is characterized by a group of carboxylates that function as a proton attractive domain [Checover, S., Nachliel, E., Dencher, N. A., and Gutman, M. (1997) Biochemistry 36, 13919-13928]. To identify these carboxylates, we selectively mutated them into cysteine residues and monitored the effects of the dynamics of proton transfer between the bulk and the surface of the protein. The measurements were carried out without attachment of a pH-sensor to the cysteine residue, thus avoiding any structural perturbation and change in the surface charge caused by the attachment of a reporter group, and the protein was in its BR state. The purple membranes were suspended in an unbuffered solution of pyranine (8-hydroxypyrene-1,3,6-trisulfonate) and exposed to a train of 1000 laser pulses (2.1 mJ/pulse, lambda = 355 nm, at 10 Hz). The excitation of the dye ejected the hydroxyl's proton, and a few nanoseconds later, a pair of free protons and ground-state pyranine anion was formed. The experimental observation was the dynamics of the relaxation of the system to the prepulse state. The observed signals were reconstructed by a numeric method that replicates the chemical reactions proceeding in the perturbed space. The detailed reconstruction of the measured signal assigned the various proton-binding sites with rate constants for proton binding and proton exchange and the pK values. Comparison of the results obtained by the various mutants indicates that the dominant proton-binding cluster of the wild-type protein consists of D104, E161, and E234. The replacement of D104 or E161 with cysteine lowered the proton binding capacity of the cluster to approximately 60% of that of the native protein. The replacement of E234 with cysteine disrupted the structure of the cluster, causing the two remaining carboxylates to function as isolated residues that do not interact with each other. The possibility of proton transfer between monomers is discussed.

Anions↗

PubMed2001

Primary reactions of sensory rhodopsins.

The first steps in the photocycles of the archaeal photoreceptor proteins sensory rhodopsin (SR) I and II from Halobacterium salinarum and SRII from Natronobacterium pharaonis have been studied by ultrafast pump/probe spectroscopy and steady-state fluorescence spectroscopy. The data for both species of the blue-light receptor SRII suggests that their primary reactions are nearly analogous with a fast decay of the excited electronic state in 300-400 fs and a transition between two red-shifted product states in 4-5 ps. Thus SRII behaves similarly to bacteriorhodopsin. In contrast for SRI at pH 6.0, which absorbs in the orange part of the spectrum, a strongly increased fluorescence quantum yield and a drastically slower and biexponential decay of the excited electronic state occurring on the picosecond time scale (5 ps and 33 ps) is observed. The results suggest that the primary reactions are controlled by the charge distribution in the vicinity of the Schiff base and demonstrate that there is no direct connection between absorption properties and reaction dynamics for the retinal protein family.

Archaeal Proteins↗

PubMed2001

Roles of cytoplasmic arginine and threonine in chloride transport by the bacteriorhodopsin mutant D85T.

In the light-driven anion pump halorhodopsin (HR), the residues arginine 200 and threonine 203 are involved in anion release at the cytoplasmic side of the membrane. Because of large sequence homology and great structural similarities between HR and bacteriorhodopsin (BR), it has been suggested that anion translocation by HR and by the chloride-pumping BR mutant BR-D85T occurs by the same mechanism. Consequently, the functions of the R200/T203 pair in HR should be the same as those of the corresponding pair in BR-D85T (R175/T178). We have put this hypothesis to a test by creating two mutants of BR-D85T in which R175 and T178 were replaced by glutamine and valine, respectively. Chloride transport activities were essentially the same for all three mutants, whereas chloride binding and the kinetics of parts of the photocycle were markedly affected by the replacement of T178. In contrast, the consequences of mutating R175 proved to be less significant. These findings are consistent with evidence obtained on HR and therefore support the idea that the respective mechanistic roles of the cytoplasmic arginine/threonine pairs in HR and BR-D85T are equal.

Anions↗

PubMed2001

The fla gene cluster is involved in the biogenesis of flagella in Halobacterium salinarum.

In this study, a flagella-related protein gene cluster is described for Halobacterium salinarum. The fla gene cluster is located upstream of the flagellin genes flgB1-3 and oriented in the opposite direction. It consists of nine open reading frames (ORFs): htpIX, a member of the halobacterial transducer protein gene family, and the genes flaD-K. The genes flaD, E, G, H, I and J share high homologies with genes from other Archaea. Interestingly, flaK shows similarities to bacterial genes involved in the regulation of flagellar synthesis. The ORFs of flaH, flaI and flaK contain sequences coding for nucleotide binding sites. Furthermore, flaI contains a motif called the bacterial type II secretion protein E signature, indicating a functional relation to members of the bacterial pili type IV-type II secretion protein superfamily. Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that the genes flaE to flaK are transcribed into one polycistronic message. In frame deletion mutants of flaI were generated by gene replacement. The deletion strain lacks motility and belongs to the fla(-) mutant class, indicating that it is deficient in flagellar biogenesis. The overall amount of flagellin protein in Delta flaI cells is reduced, although transcription of the flagellin genes is unaffected. Therefore, the flaI gene product is involved in the biosynthesis, transport or assembly of flagella in H. salinarum.

Amino Acid Sequence↗

PubMed2001

Lag1p and Lac1p are essential for the Acyl-CoA-dependent ceramide synthase reaction in Saccharomyces cerevisae.

Lag1p and Lac1p are two homologous transmembrane proteins of the endoplasmic reticulum in Saccharomyces cerevisiae. Homologous genes have been found in a wide variety of eukaryotes. In yeast, both genes, LAC1 and LAG1, are required for efficient endoplasmic reticulum-to-Golgi transport of glycosylphosphatidylinositol-anchored proteins. In this study, we show that lag1 Delta lac1 Delta cells have reduced sphingolipid levels due to a block of the fumonisin B1-sensitive and acyl-CoA-dependent ceramide synthase reaction. The sphingolipid synthesis defect in lag1 Delta lac1 Delta cells can be partially corrected by overexpression of YPC1 or YDC1, encoding ceramidases that have been reported to have acyl-CoA-independent ceramide synthesis activity. Quadruple mutant cells (lag1 Delta lac1 Delta ypc1 Delta ydc1 Delta) do not make any sphingolipids, but are still viable probably because they produce novel lipids. Moreover, lag1 Delta lac1 Delta cells are resistant to aureobasidin A, an inhibitor of the inositolphosphorylceramide synthase, suggesting that aureobasidin A may be toxic because it leads to increased ceramide levels. Based on these data, LAG1 and LAC1 are the first genes to be identified that are required for the fumonisin B1-sensitive and acyl-CoA-dependent ceramide synthase reaction.

Acyl Coenzyme A↗

PubMed2000

Structural basis of the drastically increased initial electron transfer rate in the reaction center from a Rhodopseudomonas viridis mutant described at 2.00-A resolution.

It has previously been shown that replacement of the residue His L168 with Phe (HL168F) in the Rhodopseudomonas viridis reaction center (RC) leads to an unprecedented drastic acceleration of the initial electron transfer rate. Here we describe the determination of the x-ray crystal structure at 2.00-A resolution of the HL168F RC. The electron density maps confirm that a hydrogen bond from the protein to the special pair is removed by this mutation. Compared with the wild-type RC, the acceptor of this hydrogen bond, the ring I acetyl group of the "special pair" bacteriochlorophyll, D(L), is rotated, and its acetyl oxygen is found 1.1 A closer to the bacteriochlorophyll-Mg(2+) of the other special pair bacteriochlorophyll, D(M). The rotation of this acetyl group and the increased interaction between the D(L) ring I acetyl oxygen and the D(M)-Mg(2+) provide the structural basis for the previously observed 80-mV decrease in the D(+)/D redox potential and the drastically increased rate of initial electron transfer to the accessory bacteriochlorophyll, B(A). The high quality of the electron density maps also allowed a reliable discussion of the mode of binding of the triazine herbicide terbutryn at the binding site of the secondary quinone, Q(B).

Bacteriochlorophylls↗

PubMed2000

Refinement of the geometry of the retinal binding pocket in dark-adapted bacteriorhodopsin by heteronuclear solid-state NMR distance measurements.

The bacterial proton pump bacteriorhodopsin (BR) is a 26.5 kDa seven-transmembrane helical protein. Several structural models have been published at > or =1.55 A resolution. The initial cis-trans isomerization of the retinal moiety involves structural changes within <1 A. To understand the chromophore-protein interactions that are important for light-driven proton transport, very accurate measurements of the protein geometry are required. To reveal more structural details at the site of the retinal, we have, therefore, selectively labeled the tryptophan side chains of BR with (15)N and metabolically incorporated retinal, (13)C-labeled at position 14 or 15. Using these samples, heteronuclear distances were measured with high accuracy using SFAM REDOR magic angle spinning solid-state NMR spectroscopy in dark-adapted bacteriorhodopsin. This NMR technique is applied for the first time to a high-molecular mass protein. Two retinal conformers are distinguished by their different isotropic 14-(13)C chemical shifts. Whereas the C14 position of 13-cis-15-syn-retinal is 4.2 A from [indole-(15)N]Trp86, this distance is 3.9 A in the all-trans-15-anti conformer. This latter distance allows us to check on the details of the active center of BR in the various published models derived from X-ray and electron diffraction data. The experimental approach and the results reported in this paper enforce the notion that distances between residues of a membrane protein binding pocket and a bound ligand can be determined at subangstrom resolution.

Bacteriorhodopsins↗

PubMed2000

Reduction and protonation of the secondary quinone acceptor of Rhodobacter sphaeroides photosynthetic reaction center: kinetic model based on a comparison of wild-type chromatophores with mutants carrying Arg-->Ile substitution at sites 207 and 217 in the L-subunit.

After the light-induced charge separation in the photosynthetic reaction center (RC) of Rhodobacter sphaeroides, the electron reaches, via the tightly bound ubiquinone QA, the loosely bound ubiquinone Q(B) After two subsequent flashes of light, Q(B) is reduced to ubiquinol Q(B)H2, with a semiquinone anion Q-(B) formed as an intermediate after the first flash. We studied Q(B)H2 formation in chromatophores from Rb. sphaeroides mutants that carried Arg-->Ile substitution at sites 207 and 217 in the L-subunit. While Arg-L207 is 17 A away from Q(B), Arg-L217 is closer (9 A) and contacts the Q(B)-binding pocket. From the pH dependence of the charge recombination in the RC after the first flash, we estimated deltaG(AB), the free energy difference between the Q-(A)Q(B) and Q(A)Q-(B) states, and pK212, the apparent pK of Glu-L212, a residue that is only 4 A away from Q(B). As expected, the replacement of positively charged arginines by neutral isoleucines destabilized the Q-(B) state in the L217RI mutant to a larger extent than in the L207RI one. Also as expected, pK212 increased by approximately 0.4 pH units in the L207RI mutant. The value of pK212 in the L217RI mutant decreased by 0.3 pH units, contrary to expectations. The rate of the Q-(A)Q-(B)-->Q(A)Q(B)H2 transition upon the second flash, as monitored by electrometry via the accompanying changes in the membrane potential, was two times faster in the L207RI mutant than in the wild-type, but remained essentially unchanged in the L217RI mutant. To rationalize these findings, we developed and analyzed a kinetic model of the Q-(A)Q-(B)-->Q(A)Q(B)H2 transition. The model properly described the available experimental data and provided a set of quantitative kinetic and thermodynamic parameters of the Q(B) turnover. The non-electrostatic, 'chemical' affinity of the QB site to protons proved to be as important for the attracting protons from the bulk, as the appropriate electrostatic potential. The mutation-caused changes in the chemical proton affinity could be estimated from the difference between the experimentally established pK2J2 shifts and the expected changes in the electrostatic potential at Glu-L212, calculable from the X-ray structure of the RC. Based on functional studies, structural data and kinetic modeling, we suggest a mechanistic scheme of the QB turnover. The detachment of the formed ubiquinol from its proximal position next to Glu-L212 is considered as the rate-limiting step of the reaction cycle.

Amino Acid Substitution↗

PubMed2000

Conformational relaxation following reduction of the photoactive bacteriopheophytin in reaction centers from Balstochloris viridis. Influence of mutations at position M208.

The photochemically trapped bacteriopheophytin (BPh) b radical anion in the active branch (phi(*-)A) of reaction centers (RCs) from Blastochloris (formerly called Rhodopseudomonas) viridis is characterized by 1H-ENDOR as well as optical absorption spectroscopy. The two site-directed mutants YF(M208) and YL(M208), in which tyrosine at position M208 is replaced by phenylalanine and leucine, respectively, are investigated and compared with the wild type. The residue at M208 is in close proximity to the primary electron donor, P, the monomeric bacteriochlorophyll (BCh1), B(A), and the BPh, phiA, that are involved in the transmembrane electron transfer to the quinone, Q(A), in the RC. The analysis of the ENDOR spectra of (phi(*-)A at 160 K indicates that two distinct states of phi(*-)A are present in the wild type and the mutant YF(M208). Based on a comparison with phi(*-)A in RCs of Rhodobacter sphaeroides the two states are interpreted as torsional isomers of the 3-acetyl group of phiA. Only one phi(*-)A state occurs in the mutant YL(M208). This effect of the leucine residue at position M208 is explained by steric hindrance that locks the acetyl group in one specific position. On the basis of these results, an interpretation of the optical absorption difference spectrum of the state phi(*-)AQ(*-)A is attempted. This state can be accumulated at 100 K and undergoes an irreversible change between 100 and 200 K [Tiede et al., Biochim. Biophys. Acta 892 (1987) 294-302]. The corresponding absorbance changes in the BCh1 Q(x) and Q(y) regions observed in the wild type also occur in the YF(M208) mutant but not in YL(M208). The observed changes in the wild type and YF(M208) are assigned to RCs in which the 3-acetyl group of phiA changes its orientation. It is concluded that this distinct structural relaxation of phiA can significantly affect the optical properties of B(A) and contribute to the light-induced absorption difference spectra.

Cold Temperature↗

PubMed2000

Conformational relaxation following reduction of the photoactive bacteriopheophytin in reaction centers from Blastochloris viridis. Influence of mutations at position M208.

The photochemically trapped bacteriopheophytin (BPh) b radical anion in the active branch (Phi(A)(&z.rad;-)) of reaction centers (RCs) from Blastochloris (formerly called Rhodopseudomonas) viridis is characterized by 1H-ENDOR as well as optical absorption spectroscopy. The two site-directed mutants YF(M208) and YL(M208), in which tyrosine at position M208 is replaced by phenylalanine and leucine, respectively, are investigated and compared with the wild type. The residue at M208 is in close proximity to the primary electron donor, P, the monomeric bacteriochlorophyll (BChl), B(A), and the BPh, Phi(A), that are involved in the transmembrane electron transfer to the quinone, Q(A), in the RC. The analysis of the ENDOR spectra of Phi(A)(&z.rad;-) at 160 K indicates that two distinct states of Phi(A)(&z.rad;-) are present in the wild type and the mutant YF(M208). Based on a comparison with Phi(A)(&z.rad;-) in RCs of Rhodobacter sphaeroides the two states are interpreted as torsional isomers of the 3-acetyl group of Phi(A). Only one Phi(A)(&z.rad;-) state occurs in the mutant YL(M208). This effect of the leucine residue at position M208 is explained by steric hindrance that locks the acetyl group in one specific position. On the basis of these results, an interpretation of the optical absorption difference spectrum of the state Phi(A)(&z.rad;-)Q(A)(&z.rad;-) is attempted. This state can be accumulated at 100 K and undergoes an irreversible change between 100 and 200 K [Tiede et al., Biochim. Biophys. Acta 892 (1987) 294-302]. The corresponding absorbance changes in the BChl Q(x) and Q(y) regions observed in the wild type also occur in the YF(M208) mutant but not in YL(M208). The observed changes in the wild type and YF(M208) are assigned to RCs in which the 3-acetyl group of Phi(A) changes its orientation. It is concluded that this distinct structural relaxation of Phi(A) can significantly affect the optical properties of B(A) and contribute to the light-induced absorption difference spectra.

Journal Article↗

PubMed2000

Conformations of the rhodopsin third cytoplasmic loop grafted onto bacteriorhodopsin.

BACKGROUND: The third cytoplasmic loop of rhodopsin (Rho EF) is important in signal transduction from the retinal in rhodopsin to its G protein, transducin. This loop also interacts with rhodopsin kinase, which phosphorylates light-activated rhodopsin, and arrestin, which displaces transducin from light-activated phosphorylated rhodopsin. RESULTS: We replaced eight residues of the EF loop of bacteriorhodopsin (BR) with 24 residues from the third cytoplasmic loop of bovine Rho EF. The surfaces of purple membrane containing the mutant BR (called IIIN) were imaged by atomic force microscopy (AFM) under physiological conditions to a resolution of 0.5-0.7 nm. The crystallinity and extracellular surface of IIIN were not perturbed, and the cytoplasmic surface of IIIN increased in height compared with BR, consistent with the larger loop. Ten residues of Rho EF were excised by V8 protease, revealing helices E and F in the AFM topographs. Rho EF was modeled onto the BR structure, and the envelope derived from the AFM data of IIIN was used to select probable models. CONCLUSIONS: A likely conformation of Rho EF involves some extension of helices E and F, with the tip of the loop lying over helix C and projecting towards the C terminus. This is consistent with mutagenesis data showing the TTQ transducin-binding motif close to loop CD, and cysteine cross-linking data indicating the C-terminal part of Rho EF to be close to the CD loop.

Amino Acid Sequence↗

PubMed2000

Structure of the light-driven chloride pump halorhodopsin at 1.8 A resolution.

Halorhodopsin, an archaeal rhodopsin ubiquitous in Haloarchaea, uses light energy to pump chloride through biological membranes. Halorhodopsin crystals were grown in a cubic lipidic phase, which allowed the x-ray structure determination of this anion pump at 1.8 angstrom resolution. Halorhodopsin assembles to trimers around a central patch consisting of palmitic acid. Next to the protonated Schiff base between Lys(242) and the isomerizable retinal chromophore, a single chloride ion occupies the transport site. Energetic calculations on chloride binding reveal a combination of ion-ion and ion-dipole interactions for stabilizing the anion 18 angstroms below the membrane surface. Ion dragging across the protonated Schiff base explains why chloride and proton translocation modes are mechanistically equivalent in archaeal rhodopsins.

Bacteriorhodopsins↗

PubMed2000

The three-dimensional structure of halorhodopsin to 5 A by electron crystallography: A new unbending procedure for two-dimensional crystals by using a global reference structure.

Electron microscopy does not, in principle, require highly ordered crystals to determine a high-resolution structure. Nevertheless, crystals of any type help to constrain the molecules into a more limited range of orientations and positions, from which it is easier to carry out structure determination. We describe an improved procedure for determination of crystalline disorder, which we have applied to poorly ordered two-dimensional crystals of the chloride pump halorhodopsin from Halobacterium salinarum. The new image analysis procedure involves the use of a reference projection calculated from a global three-dimensional map to carry out the initial cross-correlation analysis. Coupled with a greater number of images taken with field emission gun microscopes, this has allowed us to calculate a three-dimensional structure for halorhodopsin, in which the seven transmembrane helices and certain molecular features, such as the beta-ionone ring of retinal, are now resolved.

Bacteriorhodopsins↗

PubMed2000

Unfolding pathways of individual bacteriorhodopsins.

Atomic force microscopy and single-molecule force spectroscopy were combined to image and manipulate purple membrane patches from Halobacterium salinarum. Individual bacteriorhodopsin molecules were first localized and then extracted from the membrane; the remaining vacancies were imaged again. Anchoring forces between 100 and 200 piconewtons for the different helices were found. Upon extraction, the helices were found to unfold. The force spectra revealed the individuality of the unfolding pathways. Helices G and F as well as helices E and D always unfolded pairwise, whereas helices B and C occasionally unfolded one after the other. Experiments with cleaved loops revealed the origin of the individuality: stabilization of helix B by neighboring helices.

Amino Acid Sequence↗

PubMed2000

Unraveling photoexcited conformational changes of bacteriorhodopsin by time resolved electron paramagnetic resonance spectroscopy.

By means of time-resolved electron paramagnetic resonance (EPR) spectroscopy, the photoexcited structural changes of site-directed spin-labeled bacteriorhodopsin are studied. A complete set of cysteine mutants of the C-D loop, positions 100-107, and of the E-F loop, including the first alpha-helical turns of helices E and F, positions 154-171, was modified with a methanethiosulfonate spin label. The EPR spectral changes occurring during the photocycle are consistent with a small movement of helix C and an outward tilt of helix F. These helix movements are accompanied by a rearrangement of the E-F loop and of the C-terminal turn of helix E. The kinetic analysis of the transient EPR data and the absorbance changes in the visible spectrum reveals that the conformational change occurs during the lifetime of the M intermediate. Prominent rearrangements of nitroxide side chains in the vicinity of D96 may indicate the preparation of the reprotonation of the Schiff base. All structural changes reverse with the recovery of the bacteriorhodopsin initial state.

Amino Acid Sequence↗