1 May 2000 Heterodimeric Versus Homodimeric Structure of the Primary Electron Donor in Rhodobacter sphaeroides Reaction Centers Genetically Modified at Position M202
Eliane Nabedryk, Claudia Schulz, Frank Müh, Wolfgang Lubitz, Jacques Breton
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Abstract

Using light-induced Fourier-transform infrared (FTIR) difference spectroscopy of the photo-oxidation of the primary donor (P) in chromatophores from Rhodobacter sphaeroides, we examined a series of site-directed mutants with His M202 changed to Gly, Ser, Cys, Asn or Glu in order to assess the ability of these side chains to ligate the Mg atom of one of the two bacteriochlorophylls (BChl) constituting P. In the P QA/PQA FTIR difference spectra of the mutants HG(M202), HS(M202), HC(M202) and HN(M202), the presence of a specific electronic transition at ∼2650–2750 cm−1 as well as of associated vibrational (phase-phonon) bands at ∼1560, 1480 and 1290 cm−1 demonstrate that these mutants contain a BChl/BChl homodimer like that in native reaction centers with the charge on P shared between the two coupled BChl. In contrast, the absence of all of these bands in HE(M202) shows that this mutant contains a BChl/bacteriopheophytin heterodimer with the charge localized on the single BChl, as previously determined for the mutant HL(M202). Furthermore, the spectra of the heterodimers HE(M202) and HL(M202) are very similar in the 4000–1200 cm−1 IR range. Perturbations of the 10a-ester and 9-keto carbonyl modes for both the P and P states are observed in the homodimer mutants reflecting slight variations in the conformation and/or in position of P. These perturbations are likely to be due to a repositioning of the dimer in the new protein cavity generated by the mutation.

Eliane Nabedryk, Claudia Schulz, Frank Müh, Wolfgang Lubitz, and Jacques Breton "Heterodimeric Versus Homodimeric Structure of the Primary Electron Donor in Rhodobacter sphaeroides Reaction Centers Genetically Modified at Position M202," Photochemistry and Photobiology 71(5), 582-588, (1 May 2000). https://doi.org/10.1562/0031-8655(2000)071<0582:HVHSOT>2.0.CO;2
Received: 1 December 1999; Accepted: 1 February 2000; Published: 1 May 2000
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