With its noncatalytic domains, DNA-binding regions, and a catalytic core targeting the histone tails, LSD1-CoREST (lysine-specific demethylase 1; REST corepressor) is an ideal model system to study ...the interplay between DNA binding and histone modification in nucleosome recognition. To this end, we covalently associated LSD1-CoREST to semisynthetic nucleosomal particles. This enabled biochemical and biophysical characterizations of nucleosome binding and structural elucidation by small-angle X-ray scattering, which was extensively validated through binding assays and site-directed mutagenesis of functional interfaces. Our results suggest that LSD1-CoREST functions as an ergonomic clamp that induces the detachment of the H3 histone tail from the nucleosomal DNA to make it available for capture by the enzyme active site. The key notion emerging from these studies is the inherently competitive nature of the binding interactions because nucleosome tails, chromatin modifiers, transcription factors, and DNA represent sites for multiple and often mutually exclusive interactions.
Significance The correct and regulated readout of epigenetic marks on chromatin is essential to modulate gene expression in living cells. The regulation of chromatin accessibility is ensured by such epigenetic tags, which form a platform for the binding of specific enzymatic modules. A clear example of this mechanism is represented by the histone demethylase LSD1-CoREST, which removes methylation marks from lysine 4 of histone protein H3. We developed a crosslinking technology to capture this histone demethylase in contact with the nucleosome and used this methodology to explore the structural and biophysical properties of this complex. This is one of the very few successful attempts to visualize the molecular mechanism underlying the recognition of the nucleosomal substrate by a histone-modifying enzyme complex.
Once translocated into the cytosol of target cells, the catalytic domain (AC) of the adenylate cyclase toxin (CyaA), a major virulence factor of Bordetella pertussis, is potently activated by binding ...calmodulin (CaM) to produce supraphysiological levels of cAMP, inducing cell death. Using a combination of small-angle X-ray scattering (SAXS), hydrogen/deuterium exchange mass spectrometry (HDX-MS), and synchrotron radiation circular dichroism (SR-CD), we show that, in the absence of CaM, AC exhibits significant structural disorder, and a 75-residue-long stretch within AC undergoes a disorder-to-order transition upon CaM binding. Beyond this local folding, CaM binding induces long-range allosteric effects that stabilize the distant catalytic site, whilst preserving catalytic loop flexibility. We propose that the high enzymatic activity of AC is due to a tight balance between the CaM-induced decrease of structural flexibility around the catalytic site and the preservation of catalytic loop flexibility, allowing for fast substrate binding and product release. The CaM-induced dampening of AC conformational disorder is likely relevant to other CaM-activated enzymes.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Calmodulin (CaM) is an evolutionarily conserved eukaryotic multifunctional protein that functions as the major sensor of intracellular calcium signaling. Its calcium-modulated function regulates the ...activity of numerous effector proteins involved in a variety of physiological processes in diverse organs, from proliferation and apoptosis, to memory and immune responses. Due to the pleiotropic roles of CaM in normal and pathological cell functions, CaM antagonists are needed for fundamental studies as well as for potential therapeutic applications. Calmidazolium (CDZ) is a potent small molecule antagonist of CaM and one the most widely used inhibitors of CaM in cell biology. Yet, CDZ, as all other CaM antagonists described thus far, also affects additional cellular targets and its lack of selectivity hinders its application for dissecting calcium/CaM signaling. A better understanding of CaM:CDZ interaction is key to design analogs with improved selectivity. Here, we report a molecular characterization of CaM:CDZ complexes using an integrative structural biology approach combining SEC-SAXS, X-ray crystallography, HDX-MS, and NMR. We provide evidence that binding of a single molecule of CDZ induces an open-to-closed conformational reorientation of the two domains of CaM and results in a strong stabilization of its structural elements associated with a reduction of protein dynamics over a large time range. These CDZ-triggered CaM changes mimic those induced by CaM-binding peptides derived from physiological protein targets, despite their distinct chemical natures. CaM residues in close contact with CDZ and involved in the stabilization of the CaM:CDZ complex have been identified. Our results provide molecular insights into CDZ-induced dynamics and structural changes of CaM leading to its inhibition and open the way to the rational design of more selective CaM antagonists.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
1. Introduction 148 2. Basics of X-ray and neutron scattering 149 2.1 Elastic scattering of electromagnetic radiation by a single electron 149 2.2 Scattering by assemblies of electrons 151 2.3 ...Anomalous scattering and long wavelengths 153 2.4 Neutron scattering 153 2.5 Transmission and attenuation 155 3. Small-angle scattering from solutions 156 3.1 Instrumentation 156 3.2 The experimental scattering pattern 157 3.3 Basic scattering functions 159 3.4 Global structural parameters 161 3.4.1 Monodisperse systems 161 3.4.2 Polydisperse systems and mixtures 163 3.5 Characteristic functions 164 4. Modelling 166 4.1 Spherical harmonics 166 4.2 Shannon sampling 169 4.3 Shape determination 170 4.3.1 Modelling with few parameters: molecular envelopes 171 4.3.2 Modelling with many parameters: bead models 173 4.4 Modelling domain structure and missing parts of high-resolution models 178 4.5 Computing scattering patterns from atomic models 184 4.6 Rigid-body refinement 187 5. Applications 190 5.1 Contrast variation studies of ribosomes 190 5.2 Structural changes and catalytic activity of the allosteric enzyme ATCase 191 6. Interactions between molecules in solution 203 6.1 Linearizing the problem for moderate interactions: the second virial coefficient 204 6.2 Determination of the structure factor 205 7. Time-resolved measurements 211 8. Conclusions 215 9. Acknowledgements 216 10. References 216 A self-contained presentation of the main concepts and methods for interpretation of X-ray and neutron-scattering patterns of biological macromolecules in solution, including a reminder of the basics of X-ray and neutron scattering and a brief overview of relevant aspects of modern instrumentation, is given. For monodisperse solutions the experimental data yield the scattering intensity of the macromolecules, which depends on the contrast between the solvent and the particles as well as on their shape and internal scattering density fluctuations, and the structure factor, which is related to the interactions between macromolecules. After a brief analysis of the information content of the scattering intensity, the two main approaches for modelling the shape and/or structure of macromolecules and the global minimization schemes used in the calculations are presented. The first approach is based, in its more advanced version, on the spherical harmonics approximation and relies on few parameters, whereas the second one uses bead models with thousands of parameters. Extensions of bead modelling can be used to model domain structure and missing parts in high-resolution structures. Methods for computing the scattering patterns from atomic models including the contribution of the hydration shell are discussed and examples are given, which also illustrate that significant differences sometimes exist between crystal and solution structures. These differences are in some cases explainable in terms of rigid-body motions of parts of the structures. Results of two extensive studies – on ribosomes and on the allosteric protein aspartate transcarbamoylase – illustrate the application of the various methods. The unique bridge between equilibrium structures and thermodynamic or kinetic aspects provided by scattering techniques is illustrated by modelling of intermolecular interactions, including crystallization, based on an analysis of the structure factor and recent time-resolved work on assembly and protein folding.
A Brief Survey of State-of-the-Art BioSAXS Bizien, Thomas; Durand, Dominique; Roblina, Pierre ...
Protein and peptide letters,
01/2016, Letnik:
23, Številka:
3
Journal Article
Recenzirano
In the field of structural biology, Small Angle X-ray Scattering (SAXS) has undergone a tremendous evolution in the last two decades. From a craft reserved to a few experts in the late 80's, it has ...now turned into a high-throughput technique, following the same trend as macromolecular crystallography. Synchrotron radiation has played a key role in this evolution, by providing intense X-ray beams of high optical quality that made possible the recording of statistically meaningful data from weakly scattering biological solutions in a reasonable time. This, in turn, prompted the development of powerful and specific software for data analysis and modeling. In this mini-review, mainly addressed towards a broad readership, representing as many potential users, we try to summarize the latest aspects of evolution of BioSAXS, both conceptually and from the point of view of instrumentation. We emphasize the need for complementary experimental or computational techniques used in combination with SAXS. The great potential of these multi-pronged approaches is illustrated by a series of very recent studies covering the various ways and means of using BioSAXS.
Entry of enveloped viruses requires fusion of viral and cellular membranes, driven by conformational changes of viral glycoproteins. Crystal structures provide static pictures of pre- and post-fusion ...conformations of these proteins but the transition pathway remains elusive. Here, using several biophysical techniques, including analytical ultracentrifugation, circular dichroïsm, electron microscopy and small angle X-ray scattering, we have characterized the low-pH-induced fusogenic structural transition of a soluble form of vesicular stomatitis virus (VSV) glycoprotein G ectodomain (G(th), aa residues 1-422, the fragment that was previously crystallized). While the post-fusion trimer is the major species detected at low pH, the pre-fusion trimer is not detected in solution. Rather, at high pH, G(th) is a flexible monomer that explores a large conformational space. The monomeric population exhibits a marked pH-dependence and adopts more elongated conformations when pH decreases. Furthermore, large relative movements of domains are detected in absence of significant secondary structure modification. Solution studies are complemented by electron micrographs of negatively stained viral particles in which monomeric ectodomains of G are observed at the viral surface at both pH 7.5 and pH 6.7. We propose that the monomers are intermediates during the conformational change and thus that VSV G trimers dissociate at the viral surface during the structural transition.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The molecular mechanisms and forces involved in the translocation of bacterial toxins into host cells are still a matter of intense research. The adenylate cyclase (CyaA) toxin from Bordetella ...pertussis displays a unique intoxication pathway in which its catalytic domain is directly translocated across target cell membranes. The CyaA translocation region contains a segment, P454 (residues 454–484), which exhibits membrane‐active properties related to antimicrobial peptides. Herein, the results show that this peptide is able to translocate across membranes and to interact with calmodulin (CaM). Structural and biophysical analyses reveal the key residues of P454 involved in membrane destabilization and calmodulin binding. Mutational analysis demonstrates that these residues play a crucial role in CyaA translocation into target cells. In addition, calmidazolium, a calmodulin inhibitor, efficiently blocks CyaA internalization. It is proposed that after CyaA binding to target cells, the P454 segment destabilizes the plasma membrane, translocates across the lipid bilayer and binds calmodulin. Trapping of CyaA by the CaM:P454 interaction in the cytosol may assist the entry of the N‐terminal catalytic domain by converting the stochastic motion of the polypeptide chain through the membrane into an efficient vectorial chain translocation into host cells.
The mechanism of cell invasion by bacterial toxins is still poorly understood. The adenylate cyclase (CyaA) toxin from Bordetella pertussis, the causative agent of whooping cough, directly translocates its catalytic domain across plasma membranes. The membrane‐permeabilizing segment (yellow) of CyaA translocates across the plasma membrane and binds calmodulin (red), which assists the entry of the catalytic domain (blue) into host cells while the hydrophobic and acylation domains (green) interact with the membrane and the C‐terminal Repeat‐in‐Toxin domain (grey) remains in the extra‐cellular milieu.
Myosin VI is the only known reverse-direction myosin motor. It has an unprecedented means of amplifying movements within the motor involving rearrangements of the converter subdomain at the C ...terminus of the motor and an unusual lever arm projecting from the converter. While the average step size of a myosin VI dimer is 30–36 nm, the step size is highly variable, presenting a challenge to the lever arm mechanism by which all myosins are thought to move. Herein, we present structures of myosin VI that reveal regions of compliance that allow an uncoupling of the lead head when movement is modeled on actin. The location of the compliance restricts the possible actin binding sites and predicts the observed stepping behavior. The model reveals that myosin VI, unlike plus-end directed myosins, does not use a pure lever arm mechanism, but instead steps with a mechanism analogous to the kinesin neck-linker uncoupling model.
► Myosin VI uses a kinesin-like mechanism to step ► Compliance in the lever arm lead head is essential to attach strongly to actin ► Myosin VI does not move using a simple swinging lever arm mechanism
Many signaling and metabolic pathways rely on the ability of some of the proteins involved to undergo a substrate-induced transition between at least two structural states. Among the various models ...put forward to account for binding and activity curves of those allosteric proteins, the Monod, Wyman, and Changeux model for allostery theory has certainly been the most influential, although a central postulate, the preexisting equilibrium between the low-activity, low-affinity quaternary structure and the high-activity, high-affinity quaternary structure states in the absence of substrates, has long awaited direct experimental substantiation. Upon substrate binding, allosteric Escherichia coli aspartate transcarbamoylase adopts alternate quaternary structures, stabilized by a set of interdomain and intersubunit interactions, which are readily differentiated by their solution x-ray scattering curves. Disruption of a salt link, which is observed only in the low-activity, low-affinity quaternary structure, between Lys-143 of the regulatory chain and Asp-236 of the catalytic chain yields a mutant enzyme that is in a reversible equilibrium between at least two states in the absence of ligand, a major tenet of the Monod, Wyman, and Changeux model. By using this mutant as a magnifying glass of the structural effect of ligand binding, a comparative analysis of the binding of carbamoyl phosphate (CP) and analogs points out the crucial role of the amine group of CP in facilitating the transition toward the high-activity, high-affinity quaternary state. Thus, the cooperative binding of aspartate in aspartate transcarbamoylase appears to result from the combination of the preexisting quaternary structure equilibrium with local changes induced by CP binding.
Size‐exclusion chromatography coupled with SAXS (small‐angle X‐ray scattering), often performed using a flow‐through capillary, should allow direct collection of monodisperse sample data. However, ...capillary fouling issues and non‐baseline‐resolved peaks can hamper its efficacy. The UltraScan solution modeler (US‐SOMO) HPLC‐SAXS (high‐performance liquid chromatography coupled with SAXS) module provides a comprehensive framework to analyze such data, starting with a simple linear baseline correction and symmetrical Gaussian decomposition tools Brookes, Pérez, Cardinali, Profumo, Vachette & Rocco (2013). J. Appl. Cryst.46, 1823–1833. In addition to several new features, substantial improvements to both routines have now been implemented, comprising the evaluation of outcomes by advanced statistical tools. The novel integral baseline‐correction procedure is based on the more sound assumption that the effect of capillary fouling on scattering increases monotonically with the intensity scattered by the material within the X‐ray beam. Overlapping peaks, often skewed because of sample interaction with the column matrix, can now be accurately decomposed using non‐symmetrical modified Gaussian functions. As an example, the case of a polydisperse solution of aldolase is analyzed: from heavily convoluted peaks, individual SAXS profiles of tetramers, octamers and dodecamers are extracted and reliably modeled.
The US‐SOMO HPLC‐SAXS (high‐performance liquid chromatography coupled with small‐angle X‐ray scattering) module is an advanced tool for the comprehensive analysis of SEC‐SAXS (size‐exclusion chromatography coupled with SAXS) data. It includes baseline and band‐broadening correction routines, and Gaussian decomposition of overlapping skewed peaks into pure components.
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