Gene sequencing and characterization of the light-harvesting complex 2 from thermophilic purple sulfur bacterium Thermochromatium tepidum

Abstract

In this study, gene sequences coding for the light-harvesting (LH) 2 polypeptides from a thermophilic purple sulfur bacterium Thermochromatium tepidum are reported and characterization of the LH2 complex is described. Three sets of pucBA genes have been identified, and the gene products have been analyzed by electrophoresis and reversed-phase chromatography. The result shows that all of the genes are expressed but the distribution of the expression is not uniform. The gene products undergo post-translational modification, where two of the β-polypeptides appear to be N-terminally methylated. Absorption spectrum of the purified LH2 complex exhibits Q (y) transitions at 800 and 854 nm in dodecyl β-maltopyranoside solution, and the circular dichroism spectrum shows a "molischianum"-like characteristic. No spectral change was observed for the LH2 when the bacterium was cultured under different conditions of light intensity. In lauryl dimethylamine N-oxide (LDAO) solution, significant changes in the absorption spectrum were observed. The B850 peak decreased and blue-shifted with increasing the LDAO concentration, whereas the B800 intensity increased without change in the peak position. The spectral changes can be partially or almost completely reversed by addition of metal ions, and the divalent cations seem to be more effective. The results indicate that ionic interactions may exist between LH2, detergent molecules and metal ions. Possible mechanisms involved in the detergent- and cation-induced spectral changes are discussed.

Cryo-EM structure of a Ca2+-bound photosynthetic LH1-RC complex containing multiple αβ-polypeptides

“…1 ), then assessed by negative-stain EM using a JEM-1011 instrument (JEOL). Masses and composition of the LH1 polypeptides were measured by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF/MS) and reversed-phase HPLC, respectively, using methods described elsewhere 42 . Phospholipid and quinone contents in the purified LH1-RC were analyzed (Supplementary Fig.…”

Structural Stability of Light-harvesting Protein LH2 Adsorbed on Mesoporous Silica Supports

“…tepidum cells using the detergent lauryldimethylamine oxide (LDAO), and purified by anion-exchange chromatography. 12 Stock solutions of LH2 contained 0.1 wt% LDAO, 6.25 mM CaCl2, and 20 mM Tris-HCl (pH 7.5). The optical density of the LH2 stock solution at 800 nm was 4.0 (25 C).…”

“…The binding of large amounts of LDAO would perturb interactions between the subunit proteins, resulting in the ellipsoidal deformation of LH2. 12,22 For the thermal deformation of LH2 in bulk systems, since the B800 and B850 band properties tend to be sensitive with temperature at higher LDAO concentrations (Fig. 3), it is apparent that a larger thermal deformation of LH2 is induced in the presence of higher concentrations of LDAO; that is, the binding of large amounts of LDAO results in the LH2 structure having less thermal stability.…”

Effects of low-molecular-weight polyols on the hydration status of the light-harvesting complex 2 from Rhodobacter sphaeroides 2.4.1

“…As membrane protein, LH2s are generally solubilized in aqueous buffer solution with assistance of detergent for further study. Therefore, the aqueous components, such as detergents (ionic, non-ionic, or zwitterionic), proton, and metal ions, are supposed to influence the properties of pigments embedded in complexes through interacting with the hydrophilic C-or N-terminal domains of LH2 complex, since they are exposed directly to the aqueous phase [4,[7][8][9]. The effect of aqueous factors on function of photosynthetic pigment-protein complexes could be observed conveniently through various spectroscopic methods to monitor the conformational change, electronic energy level variation, and excitation dynamics of Crts and BChls.…”