title: Ultrafast excited-state deactivation of flavins bound to dodecin.
abstract: Dodecins, a group of flavin-binding proteins with a dodecameric quaternary structure, are able to incorporate two flavins within each of their six identical binding pockets building an aromatic tetrade with two tryptophan residues. Dodecin from the archaeal Halobacterium salinarum is a riboflavin storage device. We demonstrate that unwanted side reactions induced by reactive riboflavin species and degradation of riboflavin are avoided by ultrafast depopulation of the reactive excited state of riboflavin. Intriguingly, in this process, the staggered riboflavin dimers do not interact in ground and photoexcited states. Rather, within the tetrade assembly, each riboflavin is kept under the control of the respective adjacent tryptophan, which suggests that the stacked arrangement is a matter of optimizing the flavin load. We further identify an electron transfer in combination with a proton transfer as a central element of the effective excited state depopulation mechanism. Structural and functional comparisons of the archaeal dodecin with bacterial homologs reveal diverging evolution. Bacterial dodecins bind the flavin FMN instead of riboflavin and exhibit a clearly different binding pocket design with inverse incorporations of flavin dimers. The different adoption of flavin changes photochemical properties, making bacterial dodecin a comparably less efficient quencher of flavins. This supports a functional role different for bacterial and archaeal dodecins.
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt am Main, Max von Laue-Strasse 7, 60438 Frankfurt am Main, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Staudt
authors.affiliation: Department of Membrane Biochemistry, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Oesterhelt
authors.affiliation: Department of Membrane Biochemistry, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany. Electronic address: grininger@chemie.uni-frankfurt.de.
authors.forename: Martin
authors.initials: M
authors.lastname: Grininger
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt am Main, Max von Laue-Strasse 7, 60438 Frankfurt am Main, Germany. Electronic address: wveitl@theochem.uni-frankfurt.de.
authors.forename: Josef
authors.initials: J
authors.lastname: Wachtveitl
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism; D001419:Bacteria / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D019143:Evolution, Molecular; D005486:Flavin Mononucleotide / Q000737:chemistry* / Q000378:metabolism; D019617:Halobacterium salinarum / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D012256:Riboflavin / Q000737:chemistry* / Q000378:metabolism; D013045:Species Specificity; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism
chemical_list: D019843:Archaeal Proteins; D001426:Bacterial Proteins; D005486:Flavin Mononucleotide; D014364:Tryptophan; D012256:Riboflavin