Efficient photochemical activity and strong dichroism of single crystals of reaction centers from Rhodopseudomonas viridis

Abstract

Crystallized reaction centers from Rhodopseudomonas viridis (i) are photochemicaily active with electron transfer from the special pair to the quinones, (ii) show dichroism giving valuable.information on the orientation of the different chromophores and (iii) allow chemical treatment in the crystalline phase.In the past, reaction centers from photosynthetic bacterm have been investigated m intact cells, in photosynthetic membranes or isolated m detergent solutions. Comparison of the optical spectra of intact cells with those of isolated reaction centers suggested that careful ~solatlon does not seriously affect the properties of the reaction centers [1][2][3][4][5][6]. The spectral properues and the pigment composmon of isolated reaction centers from Rhodopseudomonas vtrtdts have been studied extenswely [1-6] Recently, the photosynthetic reaction centers from thas photosynthetic bacterium were crystallized [7]. In this paper we report on the properties of these crystals Reaction centers isolated w~th the detergent N,N-dlmethyldodecylarmne N-oxide contain four BChl b and two BPh b molecules [1] The primary electron donor, called P-960 due to its maxamum of absorbance, is made up of two of the four BChl b molecules, whale the 'primary' electron acceptor is a qulnone-lron complex [1]. There are one menaqumone and one to two ub~qumones per P-960 [8]. Isolated reacUon centers from Rps vtrt-A bbrevlatlons BChl, bactenochlorophyll, BPh, bactenopheophytm dts also contain four heme groups (two 'cytochrome c-558' and two 'cytochrome c-553'), wluch are probably bound to the same protein subumt [6], They feed electrons to P-960 +.The reaction centers were ~solated as described recently with the following modification [7]. For the molecular sieve chromatography step we used as column material Fractogel TSK HW 55 S (Merck, Darmstadt), thus step was repeated. In contrast to earher preparations [7] using different column material, we now observe bleaching of P-960 upon lllumanatlon Thus finding indicates that the qumones are still present in the new preparations. The crystals were grown as described previously [7]. The space group of these crystals IS P4~(3)2~2 with a tetragonal unit cell dlmens~on of 223 × 223 x 114 ,~ containing eight asymmetric umts per crystallographac umt cell. The volume of the asymmetric umt and the molecular wetght of the reactton centers make it more hkely that each asymmetric umt ~s occupied by two reaction center molecules than by one or three With these figures were calculate 2.8-l0 )8 reaction center molecules per cm 3, corresponding to 4.7-l0 -3 mol/1. In space group P41(3)212, a 4-fold screw axas is parallel to the z-direction whereas nomntersectlng 2-fold screw axes (perpen&cular to the 4-fold axis) are 0005-2728/83/0000-0000/$03 00

Analysis of optical spectra from single crystals of Rhodopseudomonas viridis reaction centers

“…In addition, the experimental CD spectrum of the Qy bands contains more positive than negative ellipticity and is, therefore, not conservative, in contrast to our simple theoretical description (Eqs. [5][6][7]. This may also relate to the discrepancy of the CD spectra at 790 nm.…”

“…(Q)ij = MY)Rijx A ) [6] Note that in this frame the CD spectrum is conservative i.e., the ellipticity averaged over the whole frequency regime vanishes…”

“…During the investigation, the crystals were kept in closed cells containing buffer solution (6). Thin crystal platelets (-0.2 mm x 0.1 mm x 20 sAm) with the smallest extension in the x or y direction and (0.1 mm x 0.1 mm x 20 Am) with the smallest extension in the z direction were occasionally obtained by crystallization methods.…”

“…The isolation of the reaction centers and the crystallization procedure has been described (5,6). During the investigation, the crystals were kept in closed cells containing buffer solution (6).…”

Crystallization of reaction center from Rhodopseudomonas sphaeroides: preliminary characterization.

“…Recently several membrane proteins have been crystallized (2-4), including RCs from the photosynthetic bacterium Rhodopseudomonas viridis (5), and some structural studies have been performed (6,7). However, since RCs from R. sphaeroides are smaller and have been characterized in more detail than those from R. viridis, studies on R. sphaeroides may be easier to interpret.…”