8R91

Multicopy-refined carboxymyoglobin photolysis time series at 5 mJ/cm2 laser fluence, 627 fs time delay

Summary for 8R91

• Entry DOI: 10.2210/pdb8r91/pdb
• Descriptor: Myoglobin, PROTOPORPHYRIN IX CONTAINING FE, SULFATE ION, ... (5 entities in total)
• Functional Keywords: free-electron laser, time-resolved crystallography, serial crystallography, oxygen storage
• Biological source: Equus caballus (horse)
• Total number of polymer chains: 1
• Total formula weight: 17763.09

Authors

Barends, T.,Schlichting, I. (deposition date: 2023-11-30, release date: 2024-01-31, Last modification date: 2024-03-06)

Primary citation

Barends, T.R.M.,Gorel, A.,Bhattacharyya, S.,Schiro, G.,Bacellar, C.,Cirelli, C.,Colletier, J.P.,Foucar, L.,Grunbein, M.L.,Hartmann, E.,Hilpert, M.,Holton, J.M.,Johnson, P.J.M.,Kloos, M.,Knopp, G.,Marekha, B.,Nass, K.,Nass Kovacs, G.,Ozerov, D.,Stricker, M.,Weik, M.,Doak, R.B.,Shoeman, R.L.,Milne, C.J.,Huix-Rotllant, M.,Cammarata, M.,Schlichting, I.
Influence of pump laser fluence on ultrafast myoglobin structural dynamics.
Nature, 626:905-911, 2024

PubMed Abstract: High-intensity femtosecond pulses from an X-ray free-electron laser enable pump-probe experiments for the investigation of electronic and nuclear changes during light-induced reactions. On timescales ranging from femtoseconds to milliseconds and for a variety of biological systems, time-resolved serial femtosecond crystallography (TR-SFX) has provided detailed structural data for light-induced isomerization, breakage or formation of chemical bonds and electron transfer. However, all ultrafast TR-SFX studies to date have employed such high pump laser energies that nominally several photons were absorbed per chromophore. As multiphoton absorption may force the protein response into non-physiological pathways, it is of great concern whether this experimental approach allows valid conclusions to be drawn vis-à-vis biologically relevant single-photon-induced reactions. Here we describe ultrafast pump-probe SFX experiments on the photodissociation of carboxymyoglobin, showing that different pump laser fluences yield markedly different results. In particular, the dynamics of structural changes and observed indicators of the mechanistically important coherent oscillations of the Fe-CO bond distance (predicted by recent quantum wavepacket dynamics) are seen to depend strongly on pump laser energy, in line with quantum chemical analysis. Our results confirm both the feasibility and necessity of performing ultrafast TR-SFX pump-probe experiments in the linear photoexcitation regime. We consider this to be a starting point for reassessing both the design and the interpretation of ultrafast TR-SFX pump-probe experiments such that mechanistically relevant insight emerges.

PubMed: 38355794
DOI: 10.1038/s41586-024-07032-9

Experimental method

X-RAY DIFFRACTION (1.4 Å)