Bacteriochlorin‐protein interactions in native B800‐B850, B800 deficient and B800‐Bchla_p‐reconstituted complexes from Rhodopseudomonas acidophila, strain 10050

Abstract

Recently, a method which allows the selective release and removal of the 800 nm absorbing bacteriochlorophyll a (B800) molecules from the LH2 complex of Rhodopseudomonas acidophila strain 10050 has been described [Fraser, N.J. (1999) Ph.D. Thesis, University of Glasgow, UK]. This procedure also allows the reconstitution of empty binding sites with the native pigment Bchla p , esterified with phytol. We have investigated the bacteriochlorophylla-protein interactions in native, B800 deficient (or B850) and in B800-bacteriochlorophylla p -reconstituted LH2 complexes by resonance Raman spectroscopy. We present the first direct structural evidence which shows that the reconstituted pigments are correctly bound within their binding pockets.z 1999 Federation of European Biochemical Societies.

Probing the binding sites of exchanged chlorophyll a in LH2 by Raman and site‐selection fluorescence spectroscopies

“…3b). As may be expected, the mode at 1623 cm −1 shifts to 1624/1625 cm −1 upon the removal of the Bchl a ‐B800 molecule [14]. It is worth noting that the RR spectrum of Chl‐B800‐reconstituted LH2 contains a weak band at ca.…”

“…It is worth noting that the RR spectrum of Chl‐B800‐reconstituted LH2 contains a weak band at ca. 1695–1699 cm −1 , which is not observed in the spectra of complexes devoid of the Bchl a ‐B800 molecule [14]. This weak band may arise from the keto carbonyl group of the Chl a molecule bound to the Chl‐B800‐reconstituted LH2, excited in post‐Soret resonance.…”

“…acidophila can be selectively released and replaced with native Bchl a (esterified with phytol) with near 100% efficiency [13]. By using Raman spectroscopy in resonance with the Soret transitions of the Bchl a molecules, it was shown that these molecules are correctly bound within the reconstituted complex [14]. When the conserved βHis21 residue was changed for a Ser in the related bacterium Rb.…”

Reconstitution of the Peridinin–chlorophyll a Protein (PCP): Evidence for Functional Flexibility in Chlorophyll Binding

“…The ability of different chlorophylls to replace the native chlorophyll has been well documented for B800 in the bacterial LH2 Gall et al 1999). Substitution of B800 with a series of chlorophylls whose Qy absorbance ranged from Chl a at 670 nm to 13 2 -OH-BChl at 800 nm permitted restoration of B800-B850 energy transfer but the rates of transfer were much reduced (Herek et al 2000).…”

Pigment conformation and pigment–protein interactions in the reconstituted Lhcb4 antenna protein

“…Resonance Raman spectroscopy is an ideal tool for studying these reconstituted proteins in terms of the molecular conformation of their bound pigments. It has been used extensively in the characterization of physico‐chemical mechanisms underlying the absorption properties of bacteriochlorophyll cofactors in bacterial light‐harvesting proteins [4] and to evaluate the quality of such proteins reconstituted with extrinsic pigments [5,6]. In particular, this technique allowed a quantification of the role of the different types of interactions in tuning the electronic properties of these molecules.…”