Structure-function investigations of bacterial photosynthetic reaction centers

Abstract

During photosynthesis light energy is converted into energy of chemical bonds through a series of electron and proton transfer reactions. Over the first ultrafast steps of photosynthesis that take place in the reaction center (RC) the quantum efficiency of the light energy transduction is nearly 100%. Compared to the plant and cyanobacterial photosystems, bacterial RCs are well studied and have relatively simple structure. Therefore they represent a useful model system both for manipulating of the electron transfer parameters to study detailed mechanisms of its separate steps as well as to investigate the common principles of the photosynthetic RC structure, function, and evolution. This review is focused on the research papers devoted to chemical and genetic modifications of the RCs of purple bacteria in order to study principles and mechanisms of their functioning. Investigations of the last two decades show that the maximal rates of the electron transfer reactions in the RC depend on a number of parameters. Chemical structure of the cofactors, distances between them, their relative orientation, and interactions to each other are of great importance for this process. By means of genetic and spectral methods, it was demonstrated that RC protein is also an essential factor affecting the efficiency of the photochemical charge separation. Finally, some of conservative water molecules found in RC not only contribute to stability of the protein structure, but are directly involved in the functioning of the complex.

Time-Resolved Electron Paramagnetic Resonance Study of Photoinduced Electron Transfer in Pd Porphyrin–Quinone and Zn Porphyrin–Quinone Dyads with a Cyclohexylene Spacer

“…These modifications of the D−A arrangement should affect their electronic coupling and thus influence electron transfer rates, which mimic, to some extent, conformational changes occurring in the natural photosynthetic apparatus that play a distinctive role in optimization of its high overall efficiency. 1 Here, we should notice that HyperChem modeling of our PdP-Q ensemble gives center-to-center D−A distance as ∼11 Å.…”

“…In this work we report a time-resolved electron paramagnetic resonance (TREPR) study of photoinduced intramolecular electron transfer (IET) in two artificial model systems, where the electron donors, namely PdP and ZnP are covalently linked with the same quinone acceptors via similar cyclohexylene spacers(s): (1) [S-(4(e)-(p-benzoquinonoyl)cyclohex-(e)-yl]-10,15,20-triphenylporphyrinato]palladium(II), PdP-Q, left structure in Figure 1 and (2) [S-(4(a)-(p-benzoquinonoyl)-cyclohex-(e)-yl]-10,15,20-triphenylporphyrinato]zinc(II), ZnP-Q, right structure in Figure 1.…”

“…1,2 The complexity of the in vivo apparatus prompts the search for relatively simple model systems, which can mimic the major processes occurring in photosynthetic reaction centers. 2,3 A large number of model systems where the donor (D) and acceptor (A) are linked together via various spacers and bond types have been synthesized and studied by different methods.…”

Native Mass Spectrometry Characterizes the Photosynthetic Reaction Center Complex from the Purple Bacterium Rhodobacter sphaeroides

“…The assembly also contains six types of pigments and cofactors: four bacteriochlorophyll a's (BChl), two bacteriopheophytin a's (BPh), two ubiquionines (Ubi), one spheroidene carotenoid, one non-heme iron, and one cardiolipin to yield a complex of total molecular weight (MW) of 102.5 kDa (Fig. 1) [24]. Because this RC complex is relatively small in size and has been well characterized by other methods, we chose it as a suitable model for native MS development and application.…”

Local water sensing: water exchange in bacterial photosynthetic reaction centers embedded in a trehalose glass studied using multiresonance EPR

“…[38][39][40] The three protein subunits, L, M, and H, host several cofactors 41 sequentially involved in light-driven electron transfer. The two bacteriochlorophyll a (BChl a) molecules near the periplasmic side of the membrane form the ''special pair'' P 865 .…”