title: Protein structural dynamics in solution unveiled via 100-ps time-resolved x-ray scattering.
abstract: We have developed a time-resolved x-ray scattering diffractometer capable of probing structural dynamics of proteins in solution with 100-ps time resolution. This diffractometer, developed on the ID14B BioCARS (Consortium for Advanced Radiation Sources) beamline at the Advanced Photon Source, records x-ray scattering snapshots over a broad range of q spanning 0.02-2.5 A(-1), thereby providing simultaneous coverage of the small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS) regions. To demonstrate its capabilities, we have tracked structural changes in myoglobin as it undergoes a photolysis-induced transition from its carbon monoxy form (MbCO) to its deoxy form (Mb). Though the differences between the MbCO and Mb crystal structures are small (rmsd < 0.2 A), time-resolved x-ray scattering differences recorded over 8 decades of time from 100 ps to 10 ms are rich in structure, illustrating the sensitivity of this technique. A strong, negative-going feature in the SAXS region appears promptly and corresponds to a sudden > 22 A(3) volume expansion of the protein. The ensuing conformational relaxation causes the protein to contract to a volume approximately 2 A(3) larger than MbCO within approximately 10 ns. On the timescale for CO escape from the primary docking site, another change in the SAXS/WAXS fingerprint appears, demonstrating sensitivity to the location of the dissociated CO. Global analysis of the SAXS/WAXS patterns recovered time-independent scattering fingerprints for four intermediate states of Mb. These SAXS/WAXS fingerprints provide stringent constraints for putative models of conformational states and structural transitions between them.
authors.affiliation: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA.
authors.forename: Hyun Sun
authors.initials: HS
authors.lastname: Cho
authors.forename: Naranbaatar
authors.initials: N
authors.lastname: Dashdorj
authors.forename: Friedrich
authors.initials: F
authors.lastname: Schotte
authors.forename: Timothy
authors.initials: T
authors.lastname: Graber
authors.forename: Robert
authors.initials: R
authors.lastname: Henning
authors.forename: Philip
authors.initials: P
authors.lastname: Anfinrud
mesh_terms: D000818:Animals; D001665:Binding Sites; D002248:Carbon Monoxide / Q000737:chemistry; D018360:Crystallography, X-Ray / Q000379:methods*; D006639:Histidine / Q000737:chemistry; D007700:Kinetics; D007834:Lasers; D008958:Models, Molecular; D009211:Myoglobin / Q000737:chemistry; D017785:Photons; D011506:Proteins / Q000737:chemistry*; D012542:Scattering, Radiation; D050661:Sperm Whale; D013696:Temperature; D014965:X-Rays
chemical_list: D009211:Myoglobin; D011506:Proteins; D006639:Histidine; D002248:Carbon Monoxide
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