Physical Chemistry and chemical biology combine to reveal the mechanism of action in blue light sensing proteins
BLUF domain proteins are flavoproteins which are used a light sensors by bacteria to detect sunlight and control gene expression in response to it. The molecular mechanism of this process have been uncovered in a collaborative research program between Professor Steve Meech's group in Chemistry at UEA, the Tonge group at Stony Brook University in New York and the Rutherford-Appleton laboratory near Oxford. The work is described in a recent edition of the Journal of the American Chemical Society. The rate of formation of the light adapted state occurs in two stages taking picoseconds and microseconds. The light adapted state then reverts to the dark state in minutes. Other groups showed that a critical residue was tyrosine (Y21) adjacent to the flavin ring. To probe its role we have used methods of unnatural amino acid substitution to exchange the tyrosine for a range of fluorotyrosines. Modulating the H-bond strength and the electron donation capacity. We discovered that electron transfer does not play an obvious role, but H-bond strength modifies the rate of dark reviver by a factor of 4000! (see figure) This allowed us to draw a detailed mechanism highlighting the role of H-bond reorganisation and proton transfer.