B-Side Electron Transfer in the HE(M182) Reaction Center Mutant from<i>Rhodobacter sphaeroides</i>

Katilius, Evaldas; Katiliene, Zivile; Lin, Su; Taguchi, Aileen K. W.; Woodbury, Neal W.

doi:10.1021/jp026388x

Cited by 26 publications

(47 citation statements)

References 48 publications

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“…Despite this symmetry, only one branch of the cofactors is active in the electron transfer process. Extensive characterization of modified RCs has led to the general conclusion that the asymmetry of electron transfer is largely due to differences in the energetics of the two possible pathways (21)(22)(23)(24). Models have been proposed suggesting a variety of interactions involving the cofactors that could lead to the asymmetry of electron transfer despite the overall structural symmetry; however, alterations of a significant fraction of the amino acid residues surrounding the cofactors have lead to only a limited activation of the second branch (25).…”

Section: Discussionmentioning

confidence: 99%

Interactions between lipids and bacterial reaction centers determined by protein crystallography

Cámara-Artigas

Brune

Allen

2002

Proc. Natl. Acad. Sci. U.S.A.

136

118

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The structure of the reaction center from Rhodobacter sphaeroides has been solved by using x-ray diffraction at a 2.55-Å resolution limit. Three lipid molecules that lie on the surface of the protein are resolved in the electron density maps. In addition to a cardiolipin that has previously been reported [McAuley, K. E., Fyfe, P. K., Ridge, J. P., Isaacs, N. W., Cogdell, R. J. & Jones, M. R. (1999) Proc. Natl. Acad. Sci. USA 96, 14706 -14711], two other major lipids of the cell membrane are found, a phosphatidylcholine and a glucosylgalactosyl diacylglycerol. The presence of these three lipids has been confirmed by laser mass spectroscopy. The lipids are located in the hydrophobic region of the protein surface and interact predominately with hydrophobic amino acids, in particular aromatic residues. Although the cardiolipin is over 15 Å from the cofactors, the other two lipids are in close contact with the cofactors and may contribute to the difference in energetics for the two branches of cofactors that is primarily responsible for the asymmetry of electron transfer. The glycolipid is 3.5 Å from the active bacteriochlorophyll monomer and shields this cofactor from the solvent in contrast to a much greater exposed surface evident for the inactive bacteriochlorophyll monomer. The phosphate atom of phosphatidylcholine is 6.5 Å from the inactive bacteriopheophytin, and the associated electrostatic interactions may contribute to electron transfer rates involving this cofactor. Overall, the lipids span a distance of Ϸ30 Å, which is consistent with a bilayer-like arrangement suggesting the presence of an ''inner shell'' of lipids around membrane proteins that is critical for membrane function.I ntegral membrane proteins are found in the cell membrane surrounded by lipids. The biophysical and biochemical properties of these proteins are critically determined by the lipid environment. The lipid composition of cell membranes is complex, containing a variety of phospholipids, glycolipids, and other small molecules. In the purple nonsulfur bacterium Rhodobacter sphaeroides, the major lipids are the phospholipids, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin, or diphosphatidyl glycerol, and two glycolipids, sulfoquinovosyl diacylglycerol and glucosylgalactosyl diacylglycerol (1). The relative amounts of these lipids vary significantly depending on specific growth conditions, in particular the oxygen level, although the fatty acid chains are always predominately 18:1 with only minor contributions from 18:0, 16:0, and 16:1 and trace amounts of smaller chains. The lipid composition is known to critically determine the morphology of the cell membrane, but whether the lipids can affect the photosynthetic energy conversion processes remains an outstanding question.Understanding the influence of the lipid properties on the photosynthetic complexes, or any other integral membrane proteins, is in most cases limited by the lack of detailed structural information concerning membrane proteins. To ...

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Section: Discussionmentioning

confidence: 99%

Interactions between lipids and bacterial reaction centers determined by protein crystallography

Cámara-Artigas

Brune

Allen

2002

Proc. Natl. Acad. Sci. U.S.A.

136

118

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“…[58][59][60][61] Calculations and experiments have provided estimates or bracketed ranges for the free energies of the charge-separated states in the wild-type RC: P + B L -0.05-0.1 eV below P*; 29,50,51,[62][63][64][65][66][67][68][69][70] P + H L -∼0.25 eV below P* when relaxed; [71][72][73][74][75] P + B M -0.1-0.2 eV above P* and P + H M -below P* by no more than ∼0.15 eV and probably within 0.1 eV. [50][51][52][76][77][78][79] Systematic efforts to manipulate the free energy differences of the L-and M-branch charge-separated states by site-directed mutagenesis of key amino acids, including those near B M and B L , have led to mutant RCs in which electron transfer to the M branch competes effectively with charge separation to the L branch, yielding P + H M -(reviewed in ref 80). In one such strategy in Rb.…”

Section: Introductionmentioning

confidence: 99%

Temperature Dependence of Electron Transfer to the M-Side Bacteriopheophytin in Rhodobacter capsulatus Reaction Centers

et al. 2008

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-lauryl-N,N-dimethylamine-N-oxide (LDAO) is used to suspend the RCs, the excited state of the primary electron donor (P*) decays to the ground state with an average lifetime at 77 K of 330 or 170 ps, respectively; however, in both cases the time constant obtained from single-exponential fits varies markedly as a function of the probe wavelength. These findings on the D LL RC are most easily explained in terms of a heterogeneous population of RCs. Similarly, the complex results for D LL -FY L F M in Deriphatglycerol glass at 77 K are most simply explained using a model that involves (minimally) two distinct populations of RCs with very different photochemistry. Within this framework, in 50% of the D LL -FY L F M RCs in Deriphat-glycerol glass at 77 K, P* deactivates to the ground state with a time constant of ∼400 ps, similar to the deactivation of P* in the D LL mutant at 77 K. In the other 50% of D LL -FY L F M RCs, P* has a 35 ps lifetime and decays via electron transfer to the M branch, giving P + H M -in high yield (g80%). This result indicates that P* f P + H M -is roughly a factor of 2 faster at 77 K than at 295 K. In alternative homogeneous models the rate of this M-side electron-transfer process is the same or up to 2-fold slower at low temperature. A 2-fold increase in rate with a reduction in temperature is the same behavior found for the overall L-side process P* f P + H L -in wild-type RCs. Our results suggest that, as for electron transfer on the L side, the M-side electron-transfer reaction P* f P + H M -is an activationless process.

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“…1A) the purple bacterial reaction centre exhibits a marked functional asymmetry, with only the so‐called A‐branch of cofactors between the P BChls and the Q A ubiquinone being used to catalyse transmembrane electron transfer. The structural and energetic basis of this asymmetry has been the subject of intense interest, and in recent years there have been several attempts to affect the balance of transmembrane electron transfer along the two branches through the application of site‐directed mutagenesis [15–26].…”

Section: Introductionmentioning

confidence: 99%

“…There has been a number of investigations into how the asymmetry of electron flow in the bacterial reaction centre can be changed, concentrating mainly on the picosecond time‐scale formation of the P + H B − radical pair in purified mutant reaction centres [15–26]. In the present report, we have used the Q A ‐excluding AM260W mutation as the basis for a series of multiple mutations aimed at affecting this asymmetry.…”

Section: Introductionmentioning

confidence: 99%

Photo‐accumulation of the P⁺Q_B⁻ radical pair state in purple bacterial reaction centres that lack the Q_A ubiquinone

et al. 2003

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Photo-excitation of membrane-bound Rhodobacter sphaeroides reaction centres containing the mutation Ala M260 to Trp (AM260W) resulted in the accumulation of a radical pair state involving the photo-oxidised primary electron donor (P). This state had a lifetime of hundreds of milliseconds and its formation was inhibited by stigmatellin. The absence of the Q A ubiquinone in the AM260W reaction centre suggests that this long-lived radical pair state is P + Q 3 B , although the exact reduction/protonation state of the Q B quinone remains to be con¢rmed. The blockage of active branch (A-branch) electron transfer by the AM260W mutation implies that this P + Q 3 B state is formed by electron transfer along the so-called inactive branch (B-branch) of reaction centre cofactors. We discuss how further mutations may a¡ect the yield of the P + Q 3 B state, including a double alanine mutation (EL212A/DL213A) that probably has a direct e¡ect on the e⁄ciency of the low yield electron transfer step from the anion of the B-branch bacteriopheophytin (H 3 B ) to the Q B ubiquinone.

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B-Side Electron Transfer in the HE(M182) Reaction Center Mutant fromRhodobacter sphaeroides

Cited by 26 publications

References 48 publications

Interactions between lipids and bacterial reaction centers determined by protein crystallography

Interactions between lipids and bacterial reaction centers determined by protein crystallography

Temperature Dependence of Electron Transfer to the M-Side Bacteriopheophytin in Rhodobacter capsulatus Reaction Centers

Photo‐accumulation of the P⁺Q_B⁻ radical pair state in purple bacterial reaction centres that lack the Q_A ubiquinone

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B-Side Electron Transfer in the HE(M182) Reaction Center Mutant fromRhodobacter sphaeroides

Cited by 26 publications

References 48 publications

Interactions between lipids and bacterial reaction centers determined by protein crystallography

Interactions between lipids and bacterial reaction centers determined by protein crystallography

Temperature Dependence of Electron Transfer to the M-Side Bacteriopheophytin in Rhodobacter capsulatus Reaction Centers

Photo‐accumulation of the P+QB− radical pair state in purple bacterial reaction centres that lack the QA ubiquinone

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Photo‐accumulation of the P⁺Q_B⁻ radical pair state in purple bacterial reaction centres that lack the Q_A ubiquinone