Genetic and Functional Characterisation of Rhodobacter Capsulatus Reaction Centres Carrying Triple Mutations Near to or Far from Quinone Sites

In Rhodobacter capsulatus, two triple mutants were constructed. In these non-photosynthetic mutants, two amino acids near the quinone Q_B have been mutated to two alanines: in the Q_A site have been mutated to alanine-aspartic acid and glutamic acid-alanine. Several spontaneous mutants derived from original constructs were selected. DNA sequencing experiments on originally designed mutant strains and their spontaneous mutants were performed to identify possible genetic reversions at quinone site-specific locations. Constructed mutants carry double alanines in the Q_B site and single alanine in the Q_A site. Spontaneous mutants carry additional compensating mutations, aspartic acid (L225), cysteine (M231), and serine (M231) far from Q_A and Q_B sites, which may be involved in quinone binding by the photosynthetic reaction centres.