Check out our New Publishers' Select for Free Articles

BBA - Bioenergetics (v.1787, #3)

Editorial Board (pp. i).

Cyanobacterial cytochrome c_M: Probing its role as electron donor for Cu_A of cytochrome c oxidase by Margit Bernroitner; Daniela Tangl; Chantal Lucini; Paul G. Furtmüller; Günter A. Peschek; Christian Obinger ⁎ (pp. 135-143).

It is well known that efficient functioning of photosynthetic (PET) and respiratory electron transport (RET) in cyanobacteria requires the presence of either cytochrome c₆ (Cyt c₆) or plastocyanin (PC). By contrast, the interaction of an additional redox carrier, cytochrome c_M (Cyt c_M), with either PET or RET is still under discussion. Here, we focus on the (putative) role of Cyt c_M in cyanobacterial respiration. It is demonstrated that genes encoding the main terminal oxidase (cytochrome c oxidase, COX) and cytochrome c_M are found in all 44 totally or partially sequenced cyanobacteria (except one strain). In order to check whether Cyt c_M can act as electron donor to COX, we investigated the intermolecular electron transfer kinetics between Cyt c_M and the soluble Cu_A domain (i.e. the donor binding and electron entry site) of subunit II of COX. Both proteins from Synechocystis PCC6803 were expressed heterologously in E. coli. The forward and the reverse electron transfer reactions were studied yielding apparent bimolecular rate constants of (2.4±0.1)×10⁵ M−¹ s−¹ and (9.6±0.4)×10³ M−¹ s−¹ (5 mM phosphate buffer, pH 7, 50 mM KCl). A comparative analysis with Cyt c₆ and PC demonstrates that Cyt c_M functions as electron donor to Cu_A as efficiently as Cyt c₆ but more efficient than PC. Furthermore, we demonstrate the association of Cyt c_M with the cytoplasmic and thylakoid membrane fractions by immunobloting and discuss the potential role of Cyt c_M as electron donor for COX under stress conditions.

Keywords: Abbreviations; Cyt; c; _M; cytochrome; c; _M; Cyt; c; ₆; cytochrome; c; ₆; PC; plastocyanin; hhCyt; c; horse heart cytochrome; c; cytM; gene encoding cytochrome; c; _M; petJ; gene encoding cytochrome; c; ₆; petE; gene encoding plastocyanin; COX; cytochrome; c; oxidase; SUII; subunit II; QOX; quinol oxidase; RET; respiratory electron transport chain; PET; photosynthetic electron transport chain; ET; electron transfer; PSI; photosystem I; PSII; photosystem II; ORF; open reading frame; IP; isoelectric point; EDTA; ethylene diamine tetraacetic acid; PMSF; phenylmethylsulfonyl fluorideCytochrome; c; _M; Cytochrome; c; oxidase; Copper A; Respiration; Electron transport; Stress; Stopped-flow spectroscopy kinetics

Flavodoxin: A compromise between efficiency and versatility in the electron transfer from Photosystem I to Ferredoxin-NADP⁺ reductase by Guillermina Goñi; Beatriz Herguedas; Manuel Hervás; José R. Peregrina; Miguel A. De la Rosa; Carlos Gómez-Moreno; José A. Navarro; Juan A. Hermoso; Marta Martínez-Júlvez; Milagros Medina ⁎ (pp. 144-154).

Under iron-deficient conditions Flavodoxin (Fld) replaces Ferredoxin in Anabaena as electron carrier from Photosystem I (PSI) to Ferredoxin-NADP⁺ reductase (FNR). Several residues modulate the Fld interaction with FNR and PSI, but no one appears as specifically critical for efficient electron transfer (ET). Fld shows a strong dipole moment, with its negative end directed towards the flavin ring. The role of this dipole moment in the processes of interaction and ET with positively charged surfaces exhibited by PSI and FNR has been analysed by introducing single and multiple charge reversal mutations on the Fld surface. Our data confirm that in this system interactions do not rely on a precise complementary surface of the reacting molecules. In fact, they indicate that the initial orientation driven by the alignment of dipole moment of the Fld molecule with that of the partner contributes to the formation of a bunch of alternative binding modes competent for the efficient ET reaction. Additionally, the fact that Fld uses different interaction surfaces to dock to PSI and to FNR is confirmed.

Keywords: Ferredoxin-NADP; ⁺; reductase; Flavodoxin; Protein–protein interaction; Electron transfer; Photosystem I; Transient interaction

Reversible coupling of individual phycobiliprotein isoforms during state transitions in the cyanobacterium Trichodesmium analysed by single-cell fluorescence kinetic measurements by Hendrik Küpper ⁎; Elisa Andresen; Susanna Wiegert; Miloslav Šimek; Barbara Leitenmaier; Ivan Šetlík (pp. 155-167).

In the non-heterocyst, marine cyanobacterium Trichodesmium nitrogen fixation is confined to the photoperiod and occurs coevally with oxygenic photosynthesis although nitrogenase is irreversibly inactivated by oxygen. In previous studies it was found that regulation of photosynthesis for nitrogen fixation involves Mehler reaction and various activity states with reversible coupling of photosynthetic components. We now investigated these activity states in more detail. Spectrally resolved fluorescence kinetic measurements of single cells revealed that they were related to alternate uncoupling and coupling of phycobilisomes from and to the photosystems, changing the effective cross-section of PSII. Therefore, we isolated and purified the phycobiliproteins of Trichodesmium via ion exchange chromatography and recorded their UV/VIS absorption, fluorescence excitation and fluorescence emission spectra. After describing these spectra by mathematical equations via the Gauss-Peak-Spectra method, we used them to deconvolute the in vivo fluorescence spectra of Trichodesmium cells. This revealed that the contribution of different parts of the phycobilisome antenna to fluorescence quenching changed during the daily activity cycle, and that individual phycobiliproteins can be reversibly coupled to the photosystems, while the expression levels of these proteins did not change much during the daily activity cycle. Thus we propose that variable phycobilisome coupling plays a key role in the regulation of photosynthesis for nitrogen fixation in Trichodesmium.

Keywords: Fluorescence kinetic microscopy; In vivo; spectroscopy; Nitrogen fixation; Photosynthesis; Phycobilisome; State transition

Triplet–triplet energy transfer in Peridinin-Chlorophyll a-protein reconstituted with Chl a and Chl d as revealed by optically detected magnetic resonance and pulse EPR: Comparison with the native PCP complex from Amphidinium carterae by Marilena Di Valentin; Giancarlo Agostini; Enrico Salvadori; Stefano Ceola; Giorgio Mario Giacometti; Roger G. Hiller; Donatella Carbonera ⁎ (pp. 168-175).

The triplet state of the carotenoid peridinin, populated by triplet–triplet energy transfer from photoexcited chlorophyll triplet state, in the reconstituted Peridinin-Chlorophyll a-protein, has been investigated by ODMR (Optically detected magnetic resonance), and pulse EPR spectroscopies. The properties of peridinins associated with the triplet state formation in complexes reconstituted with Chl a and Chl d have been compared to those of the main-form peridinin-chlorophyll protein (MFPCP) isolated from Amphidinium carterae. In the reconstituted samples no signals due to the presence of chlorophyll triplet states have been detected, during either steady state illumination or laser-pulse excitation. This demonstrates that reconstituted complexes conserve total quenching of chlorophyll triplet states, despite the biochemical treatment and reconstitution with the non-native Chl d pigment. Zero field splitting parameters of the peridinin triplet states are the same in the two reconstituted samples and slightly smaller than in native MFPCP. Analysis of the initial polarization of the photoinduced Electron-Spin-Echo detected spectra and their time evolution, shows that, in the reconstituted complexes, the triplet state is probably localized on the same peridinin as in native MFPCP although, when Chl d replaces Chl a, a local rearrangement of the pigments is likely to occur. Substitution of Chl d for Chl a identifies previously unassigned bands at ∼ 620 and ∼ 640 nm in the Triplet-minus-Singlet (T−S) spectrum of PCP detected at cryogenic temperature, as belonging to peridinin.

Keywords: Abbreviations; PID; peridinin; Chl; chlorophyll; PCP; peridinin-chlorophyll protein; A. carterae; Amphidinium carterae; MFPCP; main form PCP; ODMR; optically detected magnetic resonance; FDMR; fluorescence detected magnetic resonance; ADMR; absorption detected magnetic resonance; ZFS; zero field splitting; ISC; intersystem crossing; ESE; electron spin echoPCP; Peridinin; Carotenoid; Triplet; ODMR; EPR

Ca²⁺ binding to c-state of adenine nucleotide translocase (ANT)-surrounding cardiolipins enhances (ANT)-Cys⁵⁶ relative mobility: A computational-based mitochondrial permeability transition study by Cezar R. Pestana; Carlos H.T.P. Silva; Gilberto L. Pardo-Andreu; Fernando P. Rodrigues; Antonio C. Santos; Sérgio A. Uyemura; Carlos Curti ⁎ (pp. 176-182).

The oxidation of critical cysteines/related thiols of adenine nucleotide translocase (ANT) is believed to be an important event of the Ca²⁺-induced mitochondrial permeability transition (MPT), a process mediated by a cyclosporine A/ADP-sensitive permeability transition pores (PTP) opening. We addressed the ANT-Cys⁵⁶ relative mobility status resulting from the interaction of ANT/surrounding cardiolipins with Ca²⁺ and/or ADP by means of computational chemistry analysis (Molecular Interaction Fields and Molecular Dynamics studies), supported by classic mitochondrial swelling assays. The following events were predicted: (i) Ca²⁺ interacts preferentially with the ANT surrounding cardiolipins bound to the H4 helix of translocase, (ii) weakens the cardiolipins/ANT interactions and (iii) destabilizes the initial ANT-Cys⁵⁶ residue increasing its relative mobility. The binding of ADP that stabilizes the conformation “m” of ANT and/or cardiolipin, respectively to H5 and H4 helices, could stabilize their contacts with the short helix h56 that includes Cys⁵⁶, accounting for reducing its relative mobility. The results suggest that Ca²⁺ binding to adenine nucleotide translocase (ANT)-surrounding cardiolipins in c-state of the translocase enhances (ANT)-Cys⁵⁶ relative mobility and that this may constitute a potential critical step of Ca²⁺-induced PTP opening.

Keywords: Mitochondrion; Calcium; ADP; Mitochondrial permeability transition; Permeability transition pore; Adenine nucleotide translocase; Cardiolipin; Computational chemistry; Molecular interaction field; Molecular dynamics

De-novo modeling and ESR validation of a cyanobacterial F_oF₁–ATP synthase subunit bb′ left-handed coiled coil by Oleg A. Volkov; Tarek M. Zaida; Petra Voeller; Holger Lill; John G. Wise; Pia D. Vogel (pp. 183-190).

The structure and functional role of the dimeric external stalk of F_oF₁–ATP synthases have been very actively researched over the last years. To understand the function, detailed knowledge of the structure and protein packing interactions in the dimer is required. In this paper we describe the application of structural prediction and molecular modeling approaches to elucidate the structural packing interaction of the cyanobacterial ATP synthase external stalk. In addition we present biophysical evidence derived from ESR spectroscopy and site directed spin labeling of stalk proteins that supports the proposed structural model. The use of the heterodimeric bb′ dimer from a cyanobacterial ATP synthase ( Synechocystis sp. PCC 6803) allowed, by specific introduction of spin labels along each individual subunit, the evaluation of the overall tertiary structure of the subunits by calculating inter-spin distances. At defined positions in both b and b′ subunits, reporter groups were inserted to determine and confirm inter-subunit packing. The experiments showed that an approximately 100 residue long section of the cytoplasmic part of the bb′-dimer exists mostly as an elongated α-helix. The distant C-terminal end of the dimer, which is thought to interact with the δ-subunit, seemed to be disordered in experiments using soluble bb′ proteins. A left-handed coiled coil packing of the dimer suggested from structure prediction studies and shown to be feasible in molecular modeling experiments was used together with the measured inter-spin distances of the inserted reporter groups determined in ESR experiments to support the hypothesis that a significant portion of the bb′ structure exists as a left-handed coiled coil.

Keywords: ATPase; External stalk; b; -subunit; Coiled coil; De-novo modeling; Site-specific spin labeling; ESR spectroscopy

Replacement of chlorophyll with di-vinyl chlorophyll in the antenna and reaction center complexes of the cyanobacterium Synechocystis sp. PCC 6803: Characterization of spectral and photochemical properties by Tatsuya Tomo ⁎; Seiji Akimoto; Hisashi Ito; Tohru Tsuchiya; Michitaka Fukuya; Ayumi Tanaka; Mamoru Mimuro (pp. 191-200).

Chlorophyll (Chl) a in a cyanobacterium Synechocystis sp. PCC 6803 was replaced with di-vinyl (DV)-Chl a by knock-out of the specific gene ( slr1923), responsible for the reduction of a 8-vinyl group, and optical and photochemical properties of purified photosystem (PS) II complexes (DV-PS II) were investigated. We observed differences in the peak wavelengths of absorption and fluorescence spectra; however, replacement of Chl a with DV-Chl a had limited effects. On the contrary, photochemical reactions were highly sensitive to high-light treatments in the mutant. Specifically, DV-Chl a was rapidly bleached under high-light conditions, and we detected significant dissociation of complexes and degradation of D1 proteins (PsbA). By comparing the SDS-PAGE patterns observed in this study to those observed in spinach chloroplasts, this degradation is assigned to the acceptor-side photoinhibition. The delayed fluorescence in the nanosecond time region at 77 K was suppressed in DV-PS II, possibly increasing triplet formation of Chl molecules. Our findings provide insight into the evolutionary processes of cyanobacteria. The effects of pigment replacement on the optimization of reactions are discussed.

Keywords: Abbreviations; Chl; chlorophyll; DF; delayed fluorescence; DV; di-vinyl; MV; mono-vinyl; Pheo; pheophytin; PS; photosystem; RC; reaction center; TDDFT; time-dependent density functional theory; TRFS; time-resolved fluorescence spectrumDivinyl chlorophyll; Photosystem II; Delayed fluorescence; Cyanobacteria; Synechocystis; sp. PCC 6803

Time-resolved O_H→E_H transition of the aberrant ba₃ oxidase from Thermus thermophilus by Sergey A. Siletsky; Ilya Belevich; Mårten Wikström; Tewfik Soulimane; Michael I. Verkhovsky (pp. 201-205).

The kinetics of single-electron injection into the oxidized nonrelaxed state (O_H→E_H transition) of the aberrant ba₃ cytochrome oxidase from Thermus thermophilus, noted for its lowered efficiency of proton pumping, was investigated by time-resolved optical spectroscopy. Two main phases of intraprotein electron transfer were resolved. The first component ( τ∼17 μs) reflects oxidation of Cu_A and reduction of the heme groups (low-spin heme b and high-spin heme a₃ in a ratio close to 50:50). The subsequent component ( τ∼420 μs) includes reoxidation of both hemes by Cu_B. This is in significant contrast to the O_H→E_H transition of the aa₃-type cytochrome oxidase from Paracoccus denitrificans, where the fastest phase is exclusively due to transient reduction of the low-spin heme a, without electron equilibration with the binuclear center. On the other hand, the one-electron reduction of the relaxed O state in ba₃ oxidase was similar to that in aa₃ oxidase and only included rapid electron transfer from Cu_A to the low-spin heme b. This indicates a functional difference between the relaxed O and the pulsed O_H forms also in the ba₃ oxidase from T. thermophilus.

Keywords: Abbreviations; CcO; cytochrome; c; oxidase; DM; (dodecyl; L; -; D; -maltoside); E; _m; midpoint redox potential; RubiPy; tris(2,2′-bipyridyl) ruthenium; TMPD; N; ,; N; ,; N; ,; N; -tetramethyl-; p; -phenylenediamine; Tris; tris(hydroxymethyl)aminomethane; τ; time constantCatalytic cycle; Cytochrome; c; oxidase; Electron transfer; Thermus thermophilus; Cytochrome; ba; ₃

Sections

Personal tools

BBA - Bioenergetics (v.1787, #3)

Sections

Personal tools

Local resources

BBA - Bioenergetics (v.1787, #3)