title: Ligand and substrate migration in human indoleamine 2,3-dioxygenase.
abstract: Human indoleamine 2,3-dioxygenase (hIDO), a monomeric heme enzyme, catalyzes the oxidative degradation of L-Trp and other indoleamine derivatives. Using Fourier transform infrared and optical absorption spectroscopy, we have investigated the interplay between ferrous hIDO, the ligand analog CO, and the physiological substrate L-Trp. These data provide the long sought evidence for two distinct L-Trp binding sites. Upon photodissociation from the heme iron at T > 200 K, CO escapes into the solvent. Concomitantly, L-Trp exits the active site and, depending on the l-Trp concentration, migrates to a secondary binding site or into the solvent. Although L-Trp is spectroscopically silent at this site, it is still noticeable due to its pronounced effect on the CO association kinetics, which are significantly slower than those of L-Trp-free hIDO. L-Trp returns to its initial site only after CO has rebound to the heme iron.
authors.affiliation: Institute of Biophysics, University of Ulm, 89069 Ulm, Germany.
authors.forename: Elena
authors.initials: E
authors.lastname: Nickel
authors.forename: Karin
authors.initials: K
authors.lastname: Nienhaus
authors.forename: Changyuan
authors.initials: C
authors.lastname: Lu
authors.forename: Syun-Ru
authors.initials: SR
authors.lastname: Yeh
authors.forename: G Ulrich
authors.initials: GU
authors.lastname: Nienhaus
mesh_terms: D001665:Binding Sites; D002248:Carbon Monoxide / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D010782:Photolysis; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry* / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D014364:Tryptophan / Q000737:chemistry* / Q000378:metabolism
chemical_list: D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D008024:Ligands; D011994:Recombinant Proteins; D006418:Heme; D002248:Carbon Monoxide; D014364:Tryptophan