Photochemical reaction of cyanobacterial BLUF domain protein PixD

Abstract

FAD binding blue-light sensory domain BLUF is widely distributed among the genomes of photosynthetic bacteria, cyanobacteria and Euglena. PixD (Tll0078) protein of thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 is composed of only BLUF domain. BLUF domain proteins show a red-shift in the absorption spectrum of flavin upon blue light absorption. The protein structure of the PixD protein was revealed in 2005. We studied the photo-reaction of purified Tll0078 protein and its mutant proteins on Tyr8 residues expressed in E.coli by time-resolved spectroscopy and molecular dynamics simulations. The transient absorption change of wild-type protein showed the formation of 10 nm red shifted form at 50 ns after the laser excitation at room temperature. On the other hand, Y8F and Y8A mutant protein showed a formation of triplet states.