Probing binding site of bacteriochlorophyll a and carotenoid in the reconstituted LH1 complex from Rhodospirillum rubrum S1 by Stark spectroscopy

Abstract

Stark spectroscopy is a powerful technique to investigate the electrostatic interactions between pigments as well as between the pigments and the proteins in photosynthetic pigment-protein complexes. In this study, Stark spectroscopy has been used to determine two nonlinear optical parameters (polarizability change Tr(Deltaalpha) and static dipole-moment change |Deltamu| upon photoexcitation) of isolated and of reconstituted LH1 complexes from the purple photosynthetic bacterium, Rhodospirillum (Rs.) rubrum. The integral LH1 complex was prepared from Rs. rubrum S1, while the reconstituted complex was assembled by addition of purified carotenoid (all-trans-spirilloxanthin) to the monomeric subunit of LH1 from Rs. rubrum S1. The reconstituted LH1 complex has its Q(y) absorption maximum at 878 nm. This is shifted to the blue by 3 nm in comparison to the isolated LH1 complex. The energy transfer efficiency from carotenoid to bacteriochlorophyll a (BChl a), which was determined by fluorescence excitation spectroscopy of the reconstituted LH1 complex, is increased to 40%, while the efficiency in the isolated LH1 complex is only 28%. Based on the differences in the values of Tr(Deltaalpha) and |Deltamu|, between these two preparations, we can calculate the change in the electric field around the BChl a molecules in the two situations to be E (Delta) approximately 3.4 x 10(5) [V/cm]. This change can explain the 3 nm wavelength shift of the Q(y) absorption band in the reconstituted LH1 complex.

Excitation Dynamics of Two Spectral Forms of the Core Complexes from Photosynthetic Bacterium Thermochromatium tepidum

“…rubrum (28;35%) (26-28), as well as for the LH1 from Rs. rubrum G9 reconstituted with spirilloxanthin (36;40%) (28,29). The divergence in the Car-to-BChl EET efficiency is likely due to the variation in sample preparations; e.g., the LH1-RC complexes from Tch.…”

Ultra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium

“…rubrum S1 cells were grown anaerobically in the light and chromatophore membranes prepared as previously described 57 with the modification that the chromatophores were pelleted by centrifugation for one hour at 208 000 g. The LH1/RC complex was prepared as described by Nakagawa et al 58 with the exception that the β-dodecyl maltoside (DDM) was substituted for lauryldimethylamine n-oxide (LDAO). In brief, the chromatophores at an optical density (OD) of 50 at 890 nm were solubilised with 2% (w/v) DDM, and the LH1/RC complex was initially fractionated using sucrose density centrifugation with the following sucrose concentrations 0.8 M, 1.0 M, 1.2 M, 1.4 M, and 1.6 M, in 20 mM Tris-HCl, 0.02% (w/v) DDM.…”

Polarization angle dependence of stark absorption spectra of spirilloxanthin bound to the reconstituted LH1 complexes using LH1-subunits isolated from the purple photosynthetic bacterium Rhodospirillum rubrum.

“…Cultivation and harvesting of the cells of a purple photosynthetic bacterium, Rsp. rubrum wild-type strain S1, were performed as previously described (Nakagawa et al, 2008b;2009). All-trans-spirilloxanthin, the LH1 subunit-type complexes (B820 complexes) and the native LH1 complexes were isolated from Rsp.…”

“…The LH1 complexes thus obtained were dispersed in 20 mM Tris. Cl (pH 8.0) buffer solution containing 0.01% lauryldimethylamine-oxide (LDAO), and then uniformly dispersed into polyvinyl alcohol (PVA) film as reported previously (Nakagawa et al, 2008a;2008b). Briefly, 50 mg of PVA was added in 1 ml solution of LH1 at the concentration of OD 880nm about 10, and stirred overnight at 4ºC to dissolve PVA.…”