Conformational energetics of a partially symmetrized photosynthetic reaction centre

The partially symmetrized mutant reaction centre from the photosynthetic bacterium Rhodobacter capsulatus, named DLL, lacks the L-branch electron acceptor bacteriopheophytin (BPhL), thus rendering it of particular interest for experiments on primary excited states in photosynthesis. Here we present the results of conformational energy calculations on the DLL mutant and several BPhL-binding revertants. The calculations provide an explanation for the relative BPhL binding properties of the proteins in terms of interactions involving two residues in the binding pocket, these being a tryptophan and a methionine in the DLL protein.