Coffret Tacti-Paf

Linclusion passe par linvention. Pas seulement de concepts ou de services nouveaux, mais aussi dobjets répondant à des besoins que la rencontre avec le public et lorganisation dateliers co-construits ont permis de faire apparaître

Raman spectroscopic study on the conformation of 11 S form acetylcholinesterase from Torpedo californica

AbstractVibrational Raman spectroscopy has been used to study the conformation of the 11 S form of acetylcholine-sterase from Torpedo californica. Secondary structure analysis by the method of Williams [(1983) J. Mol. Biol. 166, 581–603] shows 49% α-helical structure, 23% β-sheets, 11% turns and 15% undefined structure. Secondary structure estimates obtained for this enzyme by Raman spectroscopy and circular dichroism have been analyzed

Ultrafast photochemistry of the bc₁ complex

We present a full investigation of ultrafast light-induced events in the membraneous cytochrome bc 1 complex by transient absorption spectroscopy. This energy-transducing complex harbors four redox-active components per monomer: heme c 1 , two 6-coordinate b-hemes and a [2Fe-2S] cluster. Using excitation of these components in different ratios under various excitation conditions, probing in the full visible range and under three well-defined redox conditions, we demonstrate that for all ferrous hemes of the complex photodissociation of axial ligands takes place and that they rebind in 5-7 ps, as in other 6-coordinate heme proteins, including cytoglobin, which is included as a reference in this study. By contrast, the signals are not consistent with photooxidation of the b hemes. This conclusion contrasts with a recent assessment based on a more limited data set. The binding kinetics of internal and external ligands are indicative of a rigid heme environment, consistent with the electron transfer function. We also report, for the first time, photoactivity of the very weakly absorbing iron-sulfur center. This yields the unexpected perspective of studying photochemistry, initiated by excitation of iron-sulfur clusters, in a range of protein complexes

Abstracts from the 8th International Conference on cGMP Generators, Effectors and Therapeutic Implications

This work was supported by a restricted research grant of Bayer AG

Iron transitions during activation of allosteric heme proteins in cell signaling

International audienceAllosteric heme proteins can fulfill a very large number of different functions thanks to the remarkable chemical versatility of heme through the entire living kingdom. Their efficacy resides in the ability of heme to transmit both iron coordination changes and iron redox state changes to the protein structure. Besides the properties of iron, proteins may impose a particular heme geometry leading to distortion, which allows selection or modulation of the electronic properties of heme. This review focusses on the mechanisms of allosteric protein activation triggered by heme coordination changes following diatomic binding to proteins as diverse as the human NO-receptor, cytochromes, NO-transporters and sensors, and a heme-activated potassium channel. It describes at the molecular level the chemical capabilities of heme to achieve very different tasks and emphasizes how the properties of heme are determined by the protein structure. Particularly, this reviews aims at giving an overview of the exquisite adaptability of heme, from bacteria to mammals

Functionality of nitrated acetylcholine receptor: The two-step formation of nitrotyrosines reveals their differential role in effectors binding

AbstractThe presence of nitrotyrosines is associated with several neurodegenerative pathologies. We evaluated the functionality of the nicotinic acetylcholine receptor possessing nitrotyrosines. The spectrum of the nitrated receptor displays an absorption band characteristic of ortho-nitrophenol. The presence of carbamylcholine in the agonist site prevented the effect of nitration by tetranitromethane in some conditions. The nitration occurred with two discrete steps and pointed out the differential involvement of tyrosines in the binding of acetylcholine and neurotoxin. We concluded that at least two residues involved in agonist binding can be nitrated, which bring similar contributions to the binding energy of the neurotransmitter

Photophysics of horse heart cytochrome c: time-resolved resonance Raman and transient absorption studies

International audienceTransient resonant Raman studies with 0.6 ps time resolution demonstrate that the methionine is photodissociated from ferrous, but not from ferric cytochrome c. Heme cooling and ligand recombination occur in 1.8 and 5 ps respectively. © 2004 Optical Society of Americ

Understanding the NO-sensing mechanism at molecular level

International audienceWe present here how ultrafast time-resolved spectroscopy improves our understanding of a new class of proteins: Nitric Oxide sensors. Nitric oxide (NO) is a small, short-lived, and highly reactive gaseous molecule and it acts as a second messenger in several physiological systems. NO sensors are proteins which bind NO and are able to translate this binding into a signal for mammal cells as well as in bacteria. We have studied NO-sensors with the goal of understanding the activation and deactivation mechanism of the human NO-receptor, the enzyme guanylate cyclase (sGC), which is involved in communication between cells. Some bacterial sensors of NO (SONO) have structural homologies and common properties with sGC, but also have differences with sGC which make them valuable system to get structural and physiological information on sGC. To understand how NO-sensors interact with NO and control its reactivity, it is essential to probe dynamics and interactions when NO is present within protein core and what are the associated structural changes. For this purpose, we have used time-resolved absorption spectroscopy in the picoseconds (10(-12)s) time domain. NO can be photodissociated from heme by the pulse of femtosecond laser. Time-resolved transient absorption spectra on NO-sensors were recorded and NO-protein interacttion were recorded. In case of cytochrome c', we identified the formation of 5-coordinate (5c)-NO and 5c-His hemes from 4c-heme and demonstrate that proximal histidine precludes NO rebinding at the proximal site. In bacteria, the adaptation of SONO to temperature changes was not achieved by a simple temperature-dependent NO binding equilibrium, but by a change of the proportion between 5c-NO and 6c-NO species. This amplifies the response to temperature changes since a fast NO rebinding is the only property of a 5c-NO leading to 4c-heme after dissociation. Our results of NO dynamics provide a model for the regulation at molecular level in NO-sensing function

Rebinding of proximal histidine in the Cytochrome c' from Alcaligenes xylosoxidans acts as a molecular trap for nitric oxide

International audienceTransient absorption spectra on cytochrome c' and their kinetics were recorded to identify the formation of 5-coordinate (5c)-NO and 5c-His hemes from 4c-heme (99% and 1% amplitudes; 7-ps and 100-ps time constants, respectively). We demonstrate that proximal histidine precludes NO rebinding at the proximal site

Contribution of Time-Resolved Absorption Spectroscopy to Study Biological Questions

International audienceIn this report, we illustrate through the study of two allosteric heme proteins the contribution of time-resolved absorption spectroscopy to the understanding of fundamental biological mechanisms. The first studied protein is the endogenous nitric oxide receptor (guanylate cyclase, sGC) whose activation and deactivation mechanisms are not yet fully resolved. We show that the rebinding of the proximal histidine occurs in similar to 100 picoseconds in sGC, which is the very first step of its deactivation following NO release. We also show that synergistic action of CO together with an allosteric activator induces the cleavage of the bond between heme iron and proximal histidine. The second one is the prototype of allosteric protein, the dioxygen transporter hemoglobin (Hb). In Hb, we show that the motion of the iron atom, central to the heme, moves in similar to 18 picoseconds after NO binding; this motion represents the very first step of the allosteric T -> R transition