Influence of Asn/His L166 on the Hydrogen-Bonding Pattern and Redox Potential of the Primary Donor of Purple Bacterial Reaction Centers

Ivancich, Anabella; Mattioli, Tony A.; Artz, Katie; Wang, Shaojie; Allen, James P.; Williams, Jo Ann C.

doi:10.1021/bi962516u

Cited by 20 publications

(24 citation statements)

References 45 publications

(122 reference statements)

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“…A conserved water, which is symmetry-related to water C and is assigned as 'water D', is present in this region of the protein. This water and its possible interaction with Asn L166 was previously mentioned in Ivancich et al (1997). The protein environment of His L168 is similar to that of His M197, with a few important structural differences that should be noted.…”

Section: Comparison Of Through-bond Interactions Near His M197 and His L168supporting

confidence: 56%

X-ray structure of the Rhodobacter sphaeroides reaction center with an M197 Phe→His substitution clarifies the properties of the mutant complex

Selikhanov¹,

Fufina²,

Guenther³

et al. 2022

Int Union Crystallogr J

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The first steps of the global process of photosynthesis take place in specialized membrane pigment–protein complexes called photosynthetic reaction centers (RCs). The RC of the photosynthetic purple bacterium Rhodobacter sphaeroides, a relatively simple analog of the more complexly organized photosystem II in plants, algae and cyanobacteria, serves as a convenient model for studying pigment–protein interactions that affect photochemical processes. In bacterial RCs the bacteriochlorophyll (BChl) dimer P serves as the primary electron donor, and its redox potential is a critical factor in the efficient functioning of the RC. It has previously been shown that the replacement of Phe M197 by His strongly affects the oxidation potential of P (E m P/P+), increasing its value by 125 mV, as well as increasing the thermal stability of RC and its stability in response to external pressure. The crystal structures of F(M197)H RC at high resolution obtained using various techniques presented in this report clarify the optical and electrochemical properties of the primary electron donor and the increased resistance of the mutant complex to denaturation. The electron-density maps are consistent with the donation of a hydrogen bond from the imidazole group of His M197 to the C2-acetyl carbonyl group of BChl PB. The formation of this hydrogen bond leads to a considerable out-of-plane rotation of the acetyl carbonyl group and results in a 1.2 Å shift of the O atom of this group relative to the wild-type structure. Besides, the distance between BChl PA and PB in the area of pyrrole ring I was found to be increased by up to 0.17 Å. These structural changes are discussed in association with the spectral properties of BChl dimer P. The electron-density maps strongly suggest that the imidazole group of His M197 accepts another hydrogen bond from the nearest water molecule, which in turn appears to form two more hydrogen bonds to Asn M195 and Asp L155. As a result of the F(M197)H mutation, BChl PB finds itself connected to the extensive hydrogen-bonding network that pre-existed in wild-type RC. Dissimilarities in the two hydrogen-bonding networks near the M197 and L168 sites may account for the different changes of the E m P/P+ in F(M197)H and H(L168)F RCs. The involvement of His M197 in the hydrogen-bonding network also appears to be related to stabilization of the F(M197)H RC structure. Analysis of the experimental data presented here and of the data available in the literature points to the fact that the hydrogen-bonding networks in the vicinity of BChl dimer P may play an important role in fine-tuning the redox properties of the primary electron donor.

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Section: Comparison Of Through-bond Interactions Near His M197 and His L168supporting

confidence: 56%

X-ray structure of the Rhodobacter sphaeroides reaction center with an M197 Phe→His substitution clarifies the properties of the mutant complex

Selikhanov¹,

Fufina²,

Guenther³

et al. 2022

Int Union Crystallogr J

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“…To complete this analysis, Fig. 2D shows data for all other mutations that have been constructed in the environment of the P BChls and where Δ E m P/P + has been reported [11,12,18,25–30]. Taken together with the rest of the data in Fig.…”

Section: Resultsmentioning

confidence: 99%

Tuning of the redox potential of the primary electron donor in reaction centres of purple bacteria: effects of amino acid polarity and position

2002

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Mutation of residues His L168 and Phe M197 in the reaction centre from Rhodobacter sphaeroides has an unusually strong e¡ect on the mid-point redox potential (E m ) of the pair of bacteriochlorophylls that form the primary donor of electrons, tuning E m over a range of nearly 250 mV. This e¡ect is correlated to the accompanying change in the permanent dipole of the L168 or M197 residue, suggesting it is mediated by changes in charge^dipole interactions. Comparisons with mutations made at a variety of other positions show that this correlation is particular to this residue pair, perhaps re£ecting their proximity to the ring I regions of the dimer bacteriochlorophylls that form the overlap region between these molecules. ß

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“…Experimentally, the midpoint potential of the special pair has been shifted over quite a range using site‐directed mutagenesis 15, 38–46. Our aim, through the simulation of the structure and ionization potential of the R‐26 wild type and 20 mutants of Rb.…”

Section: Our Research Programmentioning

confidence: 99%

“…It has been shown that the addition or loss of hydrogen bonds by introducing or replacing histidine, for example, into the vicinity of P changes not only the vibrational spectra 16, 18, 44 of the special pair, but also alters the midpoint potential by up to several hundred millivolts without altering the energy of the singlet excited state P* relative to the ground state 45, 47–49. Mutants constructed in order to determine secondary protein effects for residues that do not interact directly with the special pair. For example, the L166 series of mutants 40 have been designed to interact with the special pair indirectly by either enhancing or diminishing the effects of the primary residue (L168), which can form a hydrogen bond with the 2a‐acetyl oxygen of P L . Likewise, the M210 50 series of mutants were designed to either increase or decrease the electron transport properties between P and the neighboring accessory bacteriochlorophyll BPh L .…”

Section: Our Research Programmentioning

confidence: 99%

“…Mutants constructed in order to determine secondary protein effects for residues that do not interact directly with the special pair. For example, the L166 series of mutants 40 have been designed to interact with the special pair indirectly by either enhancing or diminishing the effects of the primary residue (L168), which can form a hydrogen bond with the 2a‐acetyl oxygen of P L . Likewise, the M210 50 series of mutants were designed to either increase or decrease the electron transport properties between P and the neighboring accessory bacteriochlorophyll BPh L .…”

Section: Our Research Programmentioning

confidence: 99%

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Nature of the special-pair radical cation in bacterial photosynthesis

Reimers

Hutter

Hughes

et al. 2000

Int. J. Quantum Chem.

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Primary charge separation in bacterial photosynthesis occurs at the “special pair,” a bacteriochlorophyll dimer that, on optical excitation, ejects an electron to become the special‐pair radical cation. Understanding the nature of this species is important to both the charge separation process itself and details of subsequent steps including charge recombination. Electron spin resonance (ESR)‐based studies have led to the conclusion that the positive charge is delocalized over both bacteriochlorophyll monomers, the degree of delocalization being affected by site‐directed mutagenesis. However, Breton et al. have observed charge‐transfer electronic absorption spectra (centred at ca. 2500 cm−1), which, when interpreted using standard electron‐transfer theory, indicate strong charge localization on just one of the bacteriochlorophylls. We present a complex computational strategy aimed at resolving this issue through vibronic coupling analysis of the high‐ and low‐resolution spectra using a priori computed vibrational analyses, quantum chemical calculation of the strengths of a variety of key interactions, quantum mechanical/molecular mechanical (QM/MM) calculation of the structure of over 20 mutant reaction centers, calculation and interpretation of the observed midpoint potentials, analyses relevant to ESR and related spectroscopies, etc. The current state of progress is described, leading to a consistent picture that includes almost all available experimental data. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 1224–1243, 2000

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Influence of Asn/His L166 on the Hydrogen-Bonding Pattern and Redox Potential of the Primary Donor of Purple Bacterial Reaction Centers

Cited by 20 publications

References 45 publications

X-ray structure of the Rhodobacter sphaeroides reaction center with an M197 Phe→His substitution clarifies the properties of the mutant complex

X-ray structure of the Rhodobacter sphaeroides reaction center with an M197 Phe→His substitution clarifies the properties of the mutant complex

Tuning of the redox potential of the primary electron donor in reaction centres of purple bacteria: effects of amino acid polarity and position

Nature of the special-pair radical cation in bacterial photosynthesis

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