Refinement of the x-ray structure of the RC LH1 core complex from Rhodopseudomonas palustris by single-molecule spectroscopy.

A unique combination of single-molecule spectroscopy with numerical simulations has allowed us to achieve a refined structural model for the bacteriochlorophyll a (BChl a) pigment arrangement in reaction center-light-harvesting 1 core complexes of Rhodopseudomonas palustris. Details in the optical spectra, such as spectral separation and mutual polarizations of spectral bands, are compared with results from numerical simulations for various models of the BChl a arrangement that were all well within the 4.8-A limit of the accuracy of the available x-ray structure. The experimental data are consistent with a geometry where 15 BChl a dimers, each taken homologous to those from light-harvesting 2 complex from Rhodopseudomonas acidophila, are arranged in an overall elliptical structure featuring a gap on the long side of the ellipse.