Protein structural dynamics in solution unveiled via 100-ps time-resolved x-ray scattering.
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.
Cho
Hyun Sun
HS
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA.
Dashdorj
Naranbaatar
N
Schotte
Friedrich
F
Graber
Timothy
T
Henning
Robert
R
Anfinrud
Philip
P
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
D009211:Myoglobin; D011506:Proteins; D006639:Histidine; D002248:Carbon Monoxide
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