Structure Of Photosynthetic Reaction Center Research Articles

Properties of Mutant Photosynthetic Reaction Centers of Purple Non-Sulfur Bacteria Cereibacter sphaeroides with M206 Ile→Gln Substitution

Properties of Mutant Photosynthetic Reaction Centers of Purple Non-Sulfur Bacteria Cereibacter sphaeroides with M206 Ile→Gln Substitution

Structural specificity of photosynthetic reaction centers provides high efficiency of excitation trapping and conversion.

The atomic structures of photosynthetic reaction centers of two species of purple bacteria and two photosystems 2 of cyanobacteria were resolved in the late last century. In this work I put forward the idea that of the huge body of data available thus far, only three structural factors are responsible for the unique function of conversion of physical energy of electronic excitation into electrochemical energy of separated opposite charges in reaction centers at least in purple bacteria and, perhaps, in other photosynthetic organisms.

Three-dimensional structures of photosynthetic reaction centers

In this article, the three-dimensional structures of photosynthetic reaction centers (RCs) are presented mainly on the basis of the X-ray crystal structures of the RCs from the purple bacteria Rhodopseudomonas (Rp.) viridis and Rhodobacter (Rb.) sphaeroides. In contrast to earlier comparisons and on the basis of the best-defined Rb. sphaeroides structure, a number of the reported differences between the structures cannot be confirmed. However, there are small conformational differences which might provide a basis for the explanation of observed spectral and functional discrepancies between the two species.A particular focus in this review is on the binding site of the secondary quinone (QB), where electron transfer is coupled to the uptake of protons from the cytoplasm. For the discussion of the QB site, a number of newlydetermined coordinate sets of Rp. viridis RCs modified at the QB site have been included. In addition, chains of ordered water molecules are found leading from the cytoplasm to the QB site in the best-defined structures of both Rp. viridis and Rb. sphaeroides RCs.

Two-dimensional order and protein thermal stability: high temperature preservation of structure and function

Past evidence shows that the secondary structure of photosynthetic Reaction Centres is preserved in Langmuir-Blodgett films at temperatures of up to 473 K, and that the corresponding structure in solution is lost at 328 K. This evidence is correlated with findings in this study that the functional activity of Reaction Centres is preserved up to 368 K in Langmuir-Blodgett films but only up to 308 K in dried random smears (non-oriented films). Interestingly, a similar behaviour is displayed by anti-insulin antibodies in Langmuir-Blodgett films. The role of dehydration in the preservation of secondary structure is investigated using the latter protein, and, upon comparison with the role of close packing is found to be a secondary effect. The preservation of antibody functional properties is monitored up to 423 K and unique catalytic properties appear after thermal treatment. This phenomenon is studied by making surface potential measurements and is found to be caused by the increased anisotropy of the antibody layer after thermal treatment. This increased anisotropy, related to the enhanced order of the film due to thermal treatment followed by slow cooling, is confirmed by X-ray analysis. The above evidence is collected in a unitary picture that attributes the cause of protein thermal stabilization to the close packing induced by Langmuir-Blodgett film formation; the decreased conformational entropy is implicated as the initial condition that allows protein recrystallization after thermal treatment.

Thermal stability of protein secondary structure in Langmuir-Blodgett films

The temperature dependence of the secondary structure of photosynthetic reaction centres from Rhodobacter sphaeroides in solution and in Langmuir-Blodgett film was studied by circular dichroism. It was shown that the secondary structure of the protein was not affected in Langmuir-Blodgett films by heating up to 200°C, while in solution it was completely lost at 55°C. Molecular order rather than decreased hydration degree was held responsible.

Structure of the membrane-bound protein photosynthetic reaction center from Rhodobacter sphaeroides

The structure of the photosynthetic reaction center (RC) from Rhodobacter sphaeroides was determined at 3.1-A resolution by the molecular replacement method, using the Rhodopseudomonas viridis RC as the search structure. Atomic coordinates were refined with the difference Fourier method and restrained least-squares refinement techniques to a current R factor of 22%. The tertiary structure of the RC complex is stabilized by hydrophobic interactions between the L and M chains, by interactions of the pigments with each other and with the L and M chains, by residues from the L and M chains that coordinate to the Fe2+, by salt bridges that are formed between the L and M chains and the H chain, and possibly by electrostatic forces between the ends of helices. The conserved residues at the N-termini of the L and M chains were identified as recognition sites for the H chain.

High-Resolution Structures of Photosynthetic Reaction Centers

High-Resolution Structures of Photosynthetic Reaction Centers

Crystallization of membrane proteins and structure of photosynthetic reaction centres

Crystallization of membrane proteins and structure of photosynthetic reaction centres