title: Role of active site conformational changes in photocycle activation of the AppA BLUF photoreceptor.
abstract: Blue light using flavin adenine dinucleotide (BLUF) proteins are essential for the light regulation of a variety of physiologically important processes and serve as a prototype for photoinduced proton-coupled electron transfer (PCET). Free-energy simulations elucidate the active site conformations in the AppA (activation of photopigment andpucexpression) BLUF domain before and following photoexcitation. The free-energy profile for interconversion between conformations with either Trp104 or Met106 closer to the flavin, denoted Trpin/Metoutand Trpout/Metin, reveals that both conformations are sampled on the ground state, with the former thermodynamically favorable by ∼3 kcal/mol. These results are consistent with the experimental observation of both conformations. To analyze the proton relay from Tyr21 to the flavin via Gln63, the free-energy profiles for Gln63 rotation were calculated on the ground state, the locally excited state of the flavin, and the charge-transfer state associated with electron transfer from Tyr21 to the flavin. For the Trpin/Metoutconformation, the hydrogen-bonding pattern conducive to the proton relay is not thermodynamically favorable on the ground state but becomes more favorable, corresponding to approximately half of the configurations sampled, on the locally excited state. The calculated energy gaps between the locally excited and charge-transfer states suggest that electron transfer from Tyr21 to the flavin is more facile for configurations conducive to proton transfer. When the active site conformation is not conducive to PCET from Tyr21, Trp104 can directly compete with Tyr21 for electron transfer to the flavin through a nonproductive pathway, impeding the signaling efficiency.
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
authors.forename: Puja
authors.initials: P
authors.lastname: Goyal
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801 shs3@illinois.edu.
authors.forename: Sharon
authors.identifier: 0000-0002-3782-6995
authors.initials: S
authors.lastname: Hammes-Schiffer
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000528:radiation effects; D020134:Catalytic Domain; D003198:Computer Simulation; D004579:Electron Transport; D005486:Flavin Mononucleotide / Q000737:chemistry; D005420:Flavoproteins / Q000737:chemistry* / Q000528:radiation effects; D005973:Glutamine / Q000737:chemistry; D006860:Hydrogen Bonding; D008027:Light; D008715:Methionine / Q000737:chemistry; D008958:Models, Molecular; D020283:Photoreceptors, Microbial / Q000737:chemistry* / Q000528:radiation effects; D011487:Protein Conformation / Q000528:radiation effects; D000072417:Protein Domains; D012242:Rhodobacter sphaeroides / Q000378:metabolism* / Q000528:radiation effects; D014364:Tryptophan / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry / Q000528:radiation effects
chemical_list: C116785:AppA protein, Rhodobacter sphaeroides; D001426:Bacterial Proteins; D005420:Flavoproteins; D020283:Photoreceptors, Microbial; D005973:Glutamine; D014443:Tyrosine; D005486:Flavin Mononucleotide; D014364:Tryptophan; D008715:Methionine
keywords: BLUF; electron transfer; hydrogen bonding; photoreceptor; proton transfer