Genetic and functional characterisation of Rhodobacter capsulatus reaction centres carrying triple mutations near to or far from quinone sites

Abstract

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 QB site and single alanine in the QA 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.