title: Tetramer formation kinetics in the signaling state of AppA monitored by time-resolved diffusion.
abstract: The photoreaction kinetics of the BLUF domain of AppA(5-125) was studied by monitoring time-dependence of an apparent diffusion coefficient (D) using the pulsed laser-induced transient grating technique. It was found that D of the photoproduct is time-dependent. From the concentration dependence of the reaction rate, it was concluded that the BLUF domain of AppA forms a dimer upon the photoexcitation. Since AppA exists as a dimeric form in the ground state, this dimerization reaction indicates the tetramer formation in the signaling state. From the slope of the plot of observed rate constants (k(obs)) against the AppA concentration, the second order rate constant is determined to be approximately 2.5 x 10(5) M(-1) s(-1), which is approximately 4 orders in magnitude lower than the diffusion controlled reaction. It indicates that a relative orientation of the protein molecules during the dimerization process causes additional constraints, which slow down the reaction rate.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto, Japan.
authors.forename: Partha
authors.initials: P
authors.lastname: Hazra
authors.forename: Keiichi
authors.initials: K
authors.lastname: Inoue
authors.forename: Wouter
authors.initials: W
authors.lastname: Laan
authors.forename: Klaas J
authors.initials: KJ
authors.lastname: Hellingwerf
authors.forename: Masahide
authors.initials: M
authors.lastname: Terazima
mesh_terms: D019281:Dimerization; D015226:Dinucleoside Phosphates / Q000502:physiology*; D007700:Kinetics; D007834:Lasers; D017434:Protein Structure, Tertiary / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D015226:Dinucleoside Phosphates; D011994:Recombinant Proteins; C012276:diadenosine pyrophosphate