title: Crucial role in light signal transduction for the conserved Met93 of the BLUF protein PixD/Slr1694.
abstract: PixD/Slr1694 from the cyanobacterium Synechocystis sp. PCC6803 is a member of a new class of flavin-containing blue-light sensory proteins containing a BLUF (blue light using flavin) domain. The photocycle reaction mechanism of BLUF is unique because only small structural changes of a bound chromophore are accompanied by a few hydrogen bond rearrangements in the chromophore-binding site. Here, we show that in PixD, Met93, the residue conserved in all BLUF domains, is crucial for light-dependent signal transduction. Specifically, the light-insensitive M93A mutant of PixD revealed biochemical and physiological activities compatible with those of the light-adapted wild-type PixD. However, the W91A mutant of PixD retained light sensitivity and biological function, although the corresponding mutant of another BLUF protein, AppA, has been reported to be locked in the light signaling state. These observations suggest that the pathway through which the light signal is transformed into apoprotein structural changes has been modified in BLUF proteins for their respective functions.
authors.affiliation: Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, 226-8501 Japan. shmasuda@bio.titech.ac.jp
authors.forename: Shinji
authors.initials: S
authors.lastname: Masuda
authors.forename: Koji
authors.initials: K
authors.lastname: Hasegawa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohta
authors.forename: Taka-aki
authors.initials: TA
authors.lastname: Ono
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D005420:Flavoproteins / Q000378:metabolism; D005816:Genetic Complementation Test; D008027:Light; D055537:Light Signal Transduction; D008715:Methionine / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D020283:Photoreceptors, Microbial / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D017550:Spectroscopy, Fourier Transform Infrared; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D005420:Flavoproteins; D020283:Photoreceptors, Microbial; D008715:Methionine