title: Protein conformational relaxation and ligand migration in myoglobin: a nanosecond to millisecond molecular movie from time-resolved Laue X-ray diffraction.
abstract: A time-resolved Laue X-ray diffraction technique has been used to explore protein relaxation and ligand migration at room temperature following photolysis of a single crystal of carbon monoxymyoglobin. The CO ligand is photodissociated by a 7.5 ns laser pulse, and the subsequent structural changes are probed by 150 ps or 1 micros X-ray pulses at 14 laser/X-ray delay times, ranging from 1 ns to 1.9 ms. Very fast heme and protein relaxation involving the E and F helices is evident from the data at a 1 ns time delay. The photodissociated CO molecules are detected at two locations: at a distal pocket docking site and at the Xe 1 binding site in the proximal pocket. The population by CO of the primary, distal site peaks at a 1 ns time delay and decays to half the peak value in 70 ns. The secondary, proximal docking site reaches its highest occupancy of 20% at approximately 100 ns and has a half-life of approximately 10 micros. At approximately 100 ns, all CO molecules are accounted for within the protein: in one of these two docking sites or bound to the heme. Thereafter, the CO molecules migrate to the solvent from which they rebind to deoxymyoglobin in a bimolecular process with a second-order rate coefficient of 4.5 x 10(5) M(-1) s(-1). Our results also demonstrate that structural changes as small as 0.2 A and populations of CO docking sites of 10% can be detected by time-resolved X-ray diffraction.
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Chicago, 920 East 58th Street, Chicago, Illinois 60637, USA. vusr@midway.uchicago.edu
authors.forename: V
authors.initials: V
authors.lastname: Srajer
authors.forename: Z
authors.initials: Z
authors.lastname: Ren
authors.forename: T Y
authors.initials: TY
authors.lastname: Teng
authors.forename: M
authors.initials: M
authors.lastname: Schmidt
authors.forename: T
authors.initials: T
authors.lastname: Ursby
authors.forename: D
authors.initials: D
authors.lastname: Bourgeois
authors.forename: C
authors.initials: C
authors.lastname: Pradervand
authors.forename: W
authors.initials: W
authors.lastname: Schildkamp
authors.forename: M
authors.initials: M
authors.lastname: Wulff
authors.forename: K
authors.initials: K
authors.lastname: Moffat
mesh_terms: D000818:Animals; D002248:Carbon Monoxide / Q000737:chemistry / Q000378:metabolism; D003198:Computer Simulation; D018360:Crystallography, X-Ray / Q000379:methods*; D005583:Fourier Analysis; D006207:Half-Life; D006418:Heme / Q000737:chemistry; D008024:Ligands; D008958:Models, Molecular; D009211:Myoglobin / Q000737:chemistry* / Q000378:metabolism*; D010782:Photolysis; D011485:Protein Binding; D011487:Protein Conformation; D013816:Thermodynamics; D013997:Time Factors; D014907:Whales
chemical_list: D008024:Ligands; D009211:Myoglobin; C018013:carboxymyoglobin; D006418:Heme; D002248:Carbon Monoxide