title: Detailed transient heme structures of Mb-CO in solution after CO dissociation: an X-ray transient absorption spectroscopic study.
abstract: Although understanding the structural dynamics associated with ligand photodissociation is necessary in order to correlate structure and function in biological systems, few techniques are capable of measuring the ultrafast dynamics of these systems in solution-phase at room temperature. We present here a detailed X-ray transient absorption (XTA) study of the photodissociation of CO-bound myoglobin (Fe(II)CO-Mb) in room-temperature aqueous buffer solution with a time resolution of 80 ps, along with a general procedure for handling biological samples under the harsh experimental conditions that transient X-ray experiments entail. The XTA spectra of (Fe(II)CO-Mb) exhibit significant XANES and XAFS alterations following 527 nm excitation, which remain unchanged for >47 μs. These spectral changes indicate loss of the CO ligand, resulting in a five-coordinate, domed heme, and significant energetic reorganization of the 3d orbitals of the Fe center. With the current experimental setup, each X-ray pulse in the pulse train, separated by ~153 ns, can be separately discriminated, yielding snapshots of the myoglobin evolution over time. These methods can be easily applied to other biological systems, allowing for simultaneous structural and electronic measurements of any biological system with both ultrafast and slow time resolutions, effectively mapping out all of the samples' relevant physiological processes.
authors.affiliation: Chemical Sciences and Engineering Division and X-ray Sciences Division, Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, USA.
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Stickrath
authors.forename: Michael W
authors.initials: MW
authors.lastname: Mara
authors.forename: Jenny V
authors.initials: JV
authors.lastname: Lockard
authors.forename: Michael R
authors.initials: MR
authors.lastname: Harpham
authors.forename: Jier
authors.initials: J
authors.lastname: Huang
authors.forename: Xiaoyi
authors.initials: X
authors.lastname: Zhang
authors.forename: Klaus
authors.initials: K
authors.lastname: Attenkofer
authors.forename: Lin X
authors.initials: LX
authors.lastname: Chen
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry* / Q000378:metabolism; D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry; D006418:Heme / Q000737:chemistry*; D009211:Myoglobin / Q000737:chemistry* / Q000378:metabolism; D010782:Photolysis; D017434:Protein Structure, Tertiary; D012996:Solutions / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D056928:X-Ray Absorption Spectroscopy
chemical_list: D005296:Ferrous Compounds; D009211:Myoglobin; D012996:Solutions; D006418:Heme; D002248:Carbon Monoxide