Photosynthetic reaction centre of <i>Chloroflexus aurantiacus</i> I. Primary structure of L‐subunit

The x-ray crystallographic structure of the photosynthetic reaction center (RC) has proven critical in understanding biological electron transfer processes. By contrast, understanding of intraprotein proton transfer is easily lost in the immense richness of the details. In the RC of Rhodobacter (Rb.) sphaeroides, the secondary quinone (QB) is surrounded by amino acid residues of the L subunit and some buried water molecules, with M-and H-subunit residues also close by. Studies on RCs altered by site-directed mutagenesis strongly implicate two ionizable residues in functional proton transfer to the QB binding site in Rb. sphaeroides-Glu and Asp at positions 212 and 213, respectively, of the L subunit (6-9).These are the two ionizable residues nearest to the QB head group (Fig. 1). Alteration of AspL213 to Asn had severe effects, including a-very large increase in the QAQB = QAQB equilibrium in favor of QB reduction and modification of the pH dependence of the equilibrium, especially at acid pH (7-9).Also, transfer of the second electron to QB was almost completely blocked, due to failure in the transfer of the first proton necessary for the double reduction of QB: QAQB + H+X--QAQBH-. Alteration of GluL212 to Gln also had significant effects on the quinone reactions (6,8

show abstract

“…viridis (10) and Rhodospirillum (R.) rubrum (11), as well as the less closely related species Chloroflexus (Chf.) aurantiacus (12) (14,15).…”

mentioning

confidence: 99%

Potentiation of proton transfer function by electrostatic interactions in photosynthetic reaction centers from Rhodobacter sphaeroides: First results from site-directed mutation of the H subunit.

Takahashi

Wraight

1996

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

View full text Add to dashboard Cite

show abstract

“…The comparison of amino acid sequences of L-and M-subunits of Chl. aurantiacus and purple bacteria [6,7] indicates a high extent of structural homology. According to X-ray data, the purple bacteria heterodimer structure, which consists of L-and Msubunits, is an elliptical cylinder [4].…”

Section: Results and Dlscussionmentioning

confidence: 99%

Two‐dimensional crystallization of reaction centers from Chloroflexus aurantiacus

et al. 1990

Self Cite

View full text Add to dashboard Cite

Two-dimensional crystals of photosynthetic reaction centers from CMarqkus auranfiacus were obtained from protein-lipid-detergent micelles by detergent dialysis. The size of crystals was up to 2 e. Some of them were multi~yer~ crystals. However, other crystal forms were also observed. Preliminary image processing analysis showed that crystals of one crystal form referred to two-sided piane group p2 and had the following unit cell parameters: a= 17,6 nm, b= I8,O nm, y=84". The contour map of the crystal stain-excluding region was calculated by the Fourier-filtering procedure at about 2 nm resolution.Reaction center; Two~imensionai crystal; Electron microscopy; Image processing 1" INTRODUCTIONPrimary photochemical reactions in bacterial photosynthesis are known to occur in integral membrane protein systems, i.e. reaction centers (RC). Although the detailed mechanisms of the functioning of these muitimolecular systems are still obscure, the studies of the structural organization of the photosynthetic systems at all levels are important. The membrane organization of the bacteria RC is under extensive study. The structure of the RC molecules of purple bacteria Rhodopseudoareas viridis [ 1,2] and R~odops~d~~onus sphaeroids [3,4] were determined at atomic resolution by X-ray analysis. The spatial structure of the photosynthetic RC of green bacteria C~loro~ex~s aurant~ac~s in the membrane is as yet unknown. Staehelin with coworkers analyzed a general morphology of Cklorofrexus aurantiacus bacteria 151. Recently primary structures of the L-and ~-subunits of C~~oro~~s RC were established, that allowed modeling the topography of the polypeptide chains in the membrane [S, 71.The structural organization of membrane proteins can be studied by electron microscopy of two-dimensional crystals followed by computer image reconstruction techniques [8], The present work was aimed at twodimensional crystallization of Ckloroflexus RC and 2, MATERIALS AND METHODSIsolation and purification of RC, determination of spectral and other chemical parameters were carried out as described in [4,5]. Lecithin from soybean (Sigma) was solubilized by IauryI~methyl-amine N-oxide (LDAO). For reconstitution experiments, solubilized lecithin was added to the RC sample (10 mg/ml of protein in 50 mM of Tris-HCl, pH 9.0, &l@?o LDAO) at various proportions. Then detergent was removed by dialysis under various conditions (temperature, dialysis rate, ionic strength, ion composition of dialysis media) 181.Electron microscopy studies, optical diffraction and image processing were done as described in [IO].

show abstract

“…Cells of C. uur~~Mms wcrc cultivated and RCs were isokttcd as dcscribcd in [2]. Kinetics of laser flashbinduccd absorption changes were mcasurcd using a single-beam spectrophotomctcr (41.…”

Section: Methodsmentioning

confidence: 99%

“…However, the former contain only two protein subunits, which resemble the L and M subunits of purple bacteria RCs, and lack the third H-subunit [2]. They differ also by their co-factor composition, containing 3 molecules of bacteriochlorophyll, 3 molecules of bacteriopheophytin, 2 menaquinone molecules and a manganese atom [I],…”

Section: Introductionmentioning

confidence: 99%

Functioning of quinone acceptors in the reaction center of the green photosynthetic bacterium Chloroflexus aurantiacus

et al. 1991

View full text Add to dashboard Cite

The photosynthetic reaction centers (RC) of the green bacterium Chloroflexus arrrmriucus have been investigated by spectral and electrometrical methods. In these reaction centers, the secondary quinone was found to be recc :tstituted by the addition of ubiquinone-IO. The equilibrium constant of electron transfer between primary (QA) and secondary (Qs) quinones was much higher than that in RC of purple bacteria. The Q. binding to the protein decreased under alkalinization with apparent pK 8.8. The single flash-induced electric responses were about 200 mV. An additional electrogenic phase due to the Qs protonation was observed after the second gash in the presence of exogenous electron donors. The magnitude of this phase was 18% of that related to the primary dipole (P'C&) formation. Since the C. auruntiuars RC lacks H-subunit, this subunit was not an obligatory component for electrogenic Qn protonation.

show abstract

Photosynthetic reaction centre of Chloroflexus aurantiacus I. Primary structure of L‐subunit

Cited by 109 publications

References 20 publications

Potentiation of proton transfer function by electrostatic interactions in photosynthetic reaction centers from Rhodobacter sphaeroides: First results from site-directed mutation of the H subunit.

Potentiation of proton transfer function by electrostatic interactions in photosynthetic reaction centers from Rhodobacter sphaeroides: First results from site-directed mutation of the H subunit.

Two‐dimensional crystallization of reaction centers from Chloroflexus aurantiacus

Functioning of quinone acceptors in the reaction center of the green photosynthetic bacterium Chloroflexus aurantiacus

Contact Info

Product

Resources

About