RECONSTITUTION OF THE BACTERIAL CORE LIGHT-HARVESTING COMPLEXES OF RHODOBACTER-SPHAEROIDES AND RHODOSPIRILLUM-RUBRUM WITH ISOLATED ALPHA-POLYPEPTIDES AND BETA-POLYPEPTIDES, BACTERIOCHLOROPHYLL-A, AND CAROTENOID
Cm. Davis et al., RECONSTITUTION OF THE BACTERIAL CORE LIGHT-HARVESTING COMPLEXES OF RHODOBACTER-SPHAEROIDES AND RHODOSPIRILLUM-RUBRUM WITH ISOLATED ALPHA-POLYPEPTIDES AND BETA-POLYPEPTIDES, BACTERIOCHLOROPHYLL-A, AND CAROTENOID, The Journal of biological chemistry, 270(11), 1995, pp. 5793-5804
Methodology has been developed to reconstitute carotenoids and bacteri
ochlorophyll a with isolated light-harvesting complex I (LHI) polypept
ides of both Rhodobacter sphaeroides and Rhodospirillum rubrum, Recons
titution techniques first developed in this laboratory using the LHI p
olypeptides of R. rubrum, R. sphaeroides, and Rhodobacter capsulatus r
eproduced bacteriochlorophyll a spectral properties characteristic of
LHI complexes lacking carotenoids. In this study, carotenoids are supp
lied either as organic-solvent extracts of chromatophores or as thin-l
ayer chromatography or high performance liquid chromatography-purified
species. The resulting LHI complexes exhibit carotenoid and bacterioc
hlorophyll a spectral properties characteristic of native LHI complexe
s of carotenoid-containing bacteria. Absorption and circular dichroism
spectra support the attainment of a native-like carotenoid environmen
t in the reconstituted LHI complexes. For both R. sphaeroides- and R.
rubrum-reconstituted systems, fluorescence excitation spectra reveal a
ppropriate carotenoid to bacteriochlorophyll a energy-transfer efficie
ncies based on comparisons with the in vivo systems. In the case of R,
rubrum reconstitutions, carotenoids afford protection from photodynam
ic degradation. Thus, carotenoids reconstituted into LHI exhibit spect
ral and functional characteristics associated with native pigments. He
terologous reconstitutions demonstrate the applicability of the develo
ped assay in dissecting the molecular environment of carotenoids in Li
ght-harvesting complexes.