title: ATP binding and aspartate protonation enhance photoinduced electron transfer in plant cryptochrome.
abstract: Cryptochromes are flavoproteins encountered in most vegetal and animal species. They play a role of blue-light receptors in plants and in invertebrates. The putative resting state of the FAD cofactor in these proteins is its fully oxidized form, FADox. Upon blue-light excitation, the isoalloxazine ring (ISO) may undergo an ultrafast reduction by a nearby tryptophan residue W400. This primary reduction triggers a cascade of electron and proton transfers, ultimately leading to the formation of the FADH° radical. A recent experimental study has shown that the yield of FADH° formation in Arabidopsis cryptochrome can be strongly modulated by ATP binding and by pH, affecting the protonation state of D396 (proton donor to FAD°(-)). Here we provide a detailed molecular analysis of these effects by means of combined classical molecular dynamics simulations and time-dependent density functional theory calculations. When ATP is present and D396 protonated, FAD remains in close contact with W400, thereby enhancing electron transfer (ET) from W400 to ISO*. In contrast, deprotonation of D396 and absence of ATP introduce flexibility to the photoactive site prior to FAD excitation, with the consequence of increased ISO-W400 distance and diminished tunneling rate by almost two orders of magnitude. We show that under these conditions, ET from the adenine moiety of FAD becomes a competitive relaxation pathway. Overall, our data suggest that the observed effects of ATP and pH on the FAD photoreduction find their roots in the earliest stage of the photoreduction process; i.e., ATP binding and the protonation state of D396 determine the preferred pathway of ISO* relaxation.
authors.affiliation: Laboratoire de Chimie Physique, UMR 8000, Université Paris-Sud and CNRS , Orsay F-91405, France.
authors.forename: Fabien
authors.initials: F
authors.lastname: Cailliez
authors.forename: Pavel
authors.initials: P
authors.lastname: Müller
authors.forename: Michaël
authors.initials: M
authors.lastname: Gallois
authors.forename: Aurélien
authors.initials: A
authors.lastname: de la Lande
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D017360:Arabidopsis / Q000737:chemistry / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D001224:Aspartic Acid / Q000737:chemistry / Q000378:metabolism*; D056931:Cryptochromes / Q000737:chemistry / Q000378:metabolism*; D004579:Electron Transport; D004583:Electrons; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D011522:Protons
chemical_list: D029681:Arabidopsis Proteins; C538962:CRY1 protein, Arabidopsis; D056931:Cryptochromes; D011522:Protons; D005182:Flavin-Adenine Dinucleotide; D001224:Aspartic Acid; D000255:Adenosine Triphosphate