The role of key amino acids in the photoactivation pathway of the synechocystis Slr1694 BLUF domain

Site-directed mutants with substitutions Y8W, W91F, and S28A are explored to assess the role of specific aromatic and polar residues in the Synechocystis Slr1694 BLUF (blue light sensing using FAD) protein. The results are found to be consistent with a photoactivation mechanism for BLUF domains where signaling state formation proceeds via light-driven electron and proton transfer from Y8 to FAD, followed by a hydrogen bond rearrangement and radical pair recombination.