Ultrafast dynamics in myoglobin: dark-state, CO-ligated structure
Thomas R. M. BarendsL. FoucarAlbert ArdèvolKarol NassAndrew AquilaSabine BothaR. Bruce DoakKonstantin FalahatiElisabeth HartmannM. HilpertMarcel HeinzMatthias C. HoffmannJuergen KoefingerJason E. KoglinG. KovacsovaMin LiangDespina MilathianakiH. LemkeJochen ReinsteinC.M. RoomeRobert L. ShoemanGwyn WilliamsIrène BurghardtGerhard HummerSébastien BoutetIlme Schlichting
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We report on the investigation of the photo-induced structural changes of MbNO in physiological media using ultrafast x-ray absorption spectroscopy (XAS). Pronounced changes are observed in the XANES region of the spectrum, and the NO recombination is found to occur in 216 ± 24 ps. The resulting structural analysis hints at the possibility of an intermediate structure where the NO is not completely de-ligated.
X-ray absorption spectroscopy
XANES
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Resonance Raman spectroscopy
Hemeprotein
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Oscillator strength
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Picosecond
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The dynamics of the tertiary conformation of myoglobin (Mb) after photolysis of carbon monoxide was investigated at 283 K solution by probing amide I and II bands using femtosecond IR absorption spectroscopy. Time-resolved spectra in the amide region evolve with 6-12 ps time scale without noticeable subpicosecond dynamics. The spectra measured at 100 ps delay after photolysis is similar to the difference FTIR spectrum at equilibrium. Time-resolved spectra of photoexcited Mb evolve modestly and their amplitudes are less than 8% of those of photolyzed MbCO, indicating that thermal contribution to the spectral evolution in the amide region is negligible. These observations suggest that the conformational relaxation ensuing photolysis of MbCO be complex and the final deoxy protein conformation have been substantially formed by 100 ps, probably with 6- 12 ps time constant.
Amide
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Significance This work is the first demonstration, to our knowledge, of picosecond X-ray absorption spectroscopy to probe ligand binding to heme proteins in physiological media. By Fe K-edge absorption spectroscopy, we directly interrogate the active center of the protein, delivering insight into its electronic and geometric structure. In particular, we have investigated the evolution of the Fe center after photodissociation of NO from nitrosylmyoglobin (MbNO) and observed an intermediate over hundreds of picoseconds, which we propose to be the domed ligated form of MbNO that is formed on recombination of NO to the Fe atom. This work opens the way to a detailed investigation of metalloproteins using subpicosecond X-ray spectroscopy at free electron lasers.
Photoexcitation
Picosecond
Hemeprotein
Active center
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Dynamics
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We have studied primary processes of ultrafast photoisomerization reactions of photoactive yellow protein (PYP) and visual rhodopsin (Rh) as well as ultrafast photoinduced electron transfer reactions of flavoproteins (FP) by means of the fs fluorescence up-conversion method. On the basis of these studies, we have examined the effects of the protein nanospace (PNS), where the chromophore is held, on the dynamics and mechanisms of the ultrafast and highly efficient photoinduced reactions of these proteins. In this article, we discuss mainly results of our comparative fluorescence dynamics studies on wild type (w. -t.) PYP, it’s site-directed mutants, analogues with replaced chromophore and FP, including the coherent vibrations in the ultrafast fluorescence decays of w. -t. PYP and mutants in the course of the photoisomerization, ultrafast dynamic Stokes shift of fluorescence of PYP analogues, and ultrafast electron transfer of FP.
Chromophore
Photoinduced electron transfer
Stokes shift
Protein Dynamics
Viologen
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