Crystallization and preliminary X-ray studies on the reaction center-light-harvesting 1 core complex from Rhodopseudomonas viridis

Abstract

The reaction center-light-harvesting 1 (RC-LH1) core complex is the photosynthetic apparatus in the membrane of the purple photosynthetic bacterium Rhodopseudomonas viridis. The RC is surrounded by an LH1 complex that is constituted of oligomers of three types of apoproteins (alpha, beta and gamma chains) with associated bacteriochlorophyll bs and carotenoid. It has been crystallized by the sitting-drop vapour-diffusion method. A promising crystal diffracted to beyond 8.0 A resolution. It belonged to space group P1, with unit-cell parameters a = 141.4, b = 136.9, c = 185.3 A, alpha = 104.6, beta = 94.0, gamma = 110.7 degrees. A Patterson function calculated using data between 15.0 and 8.0 A resolution suggested that the LH1 complex is distributed with quasi-16-fold rotational symmetry around the RC.

Figure 1

Sedimentation-velocity data and the sedimentation coefficient. (a) Raw sedimentation-velocity data. Experimental absorbance profile (circles) obtained at a rotor speed of 40 000 rev min⁻¹ at 293 K in 50 mM Tris–HCl pH 8.0, 0.1 M NaCl, 0.1%(w/v) DM at RC–LH1 core complex concentrations of 0.18 µM are shown. The solid lines show the best-fit sedimentation distributions. (b) Residuals of the fits corresponding to the data. (c) Distribution of the sedimentation coefficient. The distribution of the sedimentation coefficient was calculated with the Lamm equation modelling from the observed sedimentation velocity.

Figure 2

Crystals of R. viridis RC–LH1 core complex.

Figure 3

(a) χ = 180° section of the self-rotation function calculated from the data set from a R. viridis RC–LH1 core complex crystal. The resolution of the data used was 15.0–8.0 Å. The integration radius was 15–8.0 Å and the orthogonal x, y and z axes are along the a, c* × a and c* axes, respectively. (b) Polar distribution about an axis of (154°, 132°, χ) for vectors centred at the origin (self-rotation function).