title: Acquisition of photosynthetic capacity by a reaction centre that lacks the Q(A) ubiquinone; possible insights into the evolution of reaction centres?
abstract: A photosynthetically impaired strain of Rhodobacter sphaeroides containing reaction centres with an alanine to tryptophan mutation at residue 260 of the M-polypeptide (AM260W) was incubated under photosynthetic growth conditions. This incubation produced photosynthetically competent strains containing suppressor mutations that changed residue M260 to glycine or cysteine. Spectroscopic analysis demonstrated that the loss of the Q(A) ubiquinone seen in the original AM260W mutant was reversed in the suppressor mutants. In the mutant where Trp M260 was replaced by Cys, the rate of reduction of the Q(A) ubiquinone by the adjacent (H(A)) bacteriopheophytin was reduced by three-fold. The findings of the experiment are discussed in light of the X-ray crystal structures of the wild-type and AM260W reaction centres, and the possible implications for the evolution of reaction centres as bioenergetic complexes are considered.
authors.affiliation: Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, BS8 1TD Bristol, UK.
authors.forename: Marion C
authors.initials: MC
authors.lastname: Wakeham
authors.forename: Dmitrij
authors.initials: D
authors.lastname: Frolov
authors.forename: Paul K
authors.initials: PK
authors.lastname: Fyfe
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
authors.forename: Michael R
authors.initials: MR
authors.lastname: Jones
mesh_terms: D018360:Crystallography, X-Ray; D019143:Evolution, Molecular; D008027:Light; D008958:Models, Molecular; D009154:Mutation; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects; D012242:Rhodobacter sphaeroides / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects*; D013329:Structure-Activity Relationship; D014451:Ubiquinone / Q000737:chemistry*
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D011994:Recombinant Proteins; D014451:Ubiquinone