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- Mitzner, Rolf, et al.
(författare)
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L-Edge X-ray Absorption Spectroscopy of Dilute Systems Relevant to Metalloproteins Using an X-ray Free-Electron Laser
- 2013
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:21, s. 3641-3647
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Tidskriftsartikel (refereegranskat)abstract
- L-edge spectroscopy of 3d transition metals provides important electronic structure information and has been used in many fields. However, the use of this method for studying dilute aqueous systems, such as metalloenzymes, has not been prevalent because of severe radiation damage and the lack of suitable detection systems. Here we present spectra from a dilute Mn aqueous solution using a high-transmission zone-plate spectrometer at the Linac Coherent Light Source (LCLS). The spectrometer has been optimized for discriminating the Mn L-edge signal from the overwhelming 0 K-edge background that arises from water and protein itself, and the ultrashort LCLS X-ray pulses can outrun X-ray induced damage. We show that the deviations of the partial-fluorescence yield-detected spectra from the true absorption can be well modeled using the state-dependence of the fluorescence yield, and discuss implications for the application of our concept to biological samples.
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- Lassalle, A., et al.
(författare)
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Effect of visual stimuli of pain on empathy brain network in people with and without Autism Spectrum Disorder
- 2018
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Ingår i: European Journal of Neuroscience. - : Wiley. - 0953-816X .- 1460-9568. ; 48:6, s. 2333-2342
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Tidskriftsartikel (refereegranskat)abstract
- The extent to which affective empathy is impaired in Autism Spectrum Disorder (ASD) remains unclear, as some-but not all-previous neuroimaging studies investigating empathy for pain in ASD have shown similar activation levels to those of neurotypicals individuals. These inconsistent results could be due to the use of different empathy-eliciting stimuli. While some studies used pictures of faces exhibiting a painful expression, others used pictures of limbs in painful situations. In this study, we used fMRI to compare activation in areas associated with empathy processing (empathy network) for these two types of stimuli in 31 participants (16 with ASD, 15 controls). We found a group difference in the inferior frontal gyrus (IFG) and the thalamus when participants viewed stimuli of limbs in painful situations, but not when they viewed face stimuli with a painful expression. Both groups of participants activated their empathy network more when viewing pictures of limbs in painful situations than when viewing pictures of faces with a painful expression; this increased activation for limbs versus faces was significantly enhanced in controls relative to ASD participants, especially in the secondary somatosensory cortex (SII). Our findings suggest that empathy defect of people with ASD is contingent upon the type of stimuli used, and may be related to the level of Mirror Neuron System involvement, as brain regions showing group differences (IFG, SII) underlie embodiment. We discuss the potential clinical implications of our findings in terms of developing interventions boosting the empathetic abilities of people with ASD.
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- Lassalle, L., et al.
(författare)
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Structure of intermediates of the water oxidation reaction in photosystem II
- 2019
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Ingår i: Acta Crystallographica Section A. - : International Union of Crystallography. - 2053-2733. ; A75
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Photosystem II (PSII) catalyzes the light driven oxidation of water into dioxygen, protons and electrons. This reaction takes place at the oxygen evolving complex (OEC) a Mn4CaO5 cluster, through five intermediate S-states (S0 to S4), S1 being the dark-stable state and S3 the highest oxidized semi-stable state before O-O bond formation and O2 evolution. We have been using fs X-ray pulses from an X-ray free electron laser (XFEL) to study the geometric and electronic structure of the OEC over the reaction cycle and recently reported high-resolution (around 2 Å) structures of PSII at room temperature for the four stable states in the S-state cycle as well as for two time points in the S2-S3 transition. Our results reveal important structural changes including the binding of one additional ‘water’, Ox, during the S2→S3 state transition. The binding of the additional oxygen Ox in the S3 state between Ca and Mn1 suggests O-O bond formation mechanisms involving O5 as one substrate, where Ox is either the other substrate oxygen or is perfectly positioned to refill the O5 position during O2 release. We also explored the extended network of H-bonds between amino acid residues and waters connecting the OEC to the bulk solvent. We observed several significant changes in this network during the S-state cycle. Based on these data we will discuss the dynamics of the catalytic site and its environment over the reaction cycle.
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