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Bond dissociation energies of X–H bonds in proteins

Abstract (Expand)

Knowledge of reliable X−H bond dissociation energies (X = C, N, O, S) for amino acids in proteins is key for studying the radical chemistry of proteins. X−H bond dissociation energies of model dipeptides … were computed using the isodesmic reaction method at the BMK/6-31+G(2df,p) and G4(MP2)-6X levels of theory. The density functional theory values agree well with the composite- level calculations. By this high level of theory, combined with a careful choice of reference compounds and peptide model systems, our work provides a highly valuable data set of bond dissociation energies with unprecedented accuracy and comprehensiveness. It will likely prove useful to predict protein biochemistry involving radicals, e.g., by machine learning.

Authors: Authors Wojtek Treyde, Kai Riedmiller, Frauke Gräter

Date Published: 1st Dec 2022

Publication Type: Journal

Structure and dynamics of the von Willebrand Factor C6 domain

Abstract (Expand)

Von Willebrand disease (VWD) is a bleeding disorder with different levels of severity. VWD-associated mutations are located in the von Willebrand factor (VWF) gene, coding for the large multidomain … plasma protein VWF with essential roles in hemostasis and thrombosis. On the one hand, a variety of mutations in the C-domains of VWF are associated with increased bleeding upon vascular injury. On the other hand, VWF gain-of-function (GOF) mutations in the C4 domain have recently been identified, which induce an increased risk of myocardial infarction. Mechanistic insights into how these mutations affect the molecular behavior of VWF are scarce and holistic approaches are challenging due to the multidomain and multimeric character of this large protein. Here, we determine the structure and dynamics of the C6 domain and the single nucleotide polymorphism (SNP) variant G2705R in C6 by combining nuclear magnetic resonance spectroscopy, molecular dynamics simulations and aggregometry. Our findings indicate that this mutation mostly destabilizes VWF by leading to a more pronounced hinging between both subdomains of C6. Hemostatic parameters of variant G2705R are close to normal under static conditions, but the missense mutation results in a gain-of-function under flow conditions, due to decreased VWF stem stability. Together with the fact that two C4 variants also exhibit GOF characteristics, our data underline the importance of the VWF stem region in VWF’s hemostatic activity and the risk of mutation-associated prothrombotic properties in VWF C-domain variants due to altered stem dynamics.

Authors: Po-Chia Chen, Fabian Kutzki, Angelika Mojzisch, Bernd Simon, Emma-Ruoqi Xu, Camilo Aponte-Santamaría, Kai Horny, Cy Jeffries, Reinhard Schneppenheim, Matthias Wilmanns, Maria A. Brehm, Frauke Gräter, Janosch Hennig

Date Published: 18th Nov 2022

Publication Type: Journal

Hydropersulfides inhibit lipid peroxidation and ferroptosis by scavenging radicals

Abstract (Expand)

erroptosis is a type of cell death caused by radical-driven lipid peroxidation, leading to membrane damage and rupture. Here we show that enzymatically produced sulfane sulfur (S0) species, specifically … hydropersulfides, scavenge endogenously generated free radicals and, thereby, suppress lipid peroxidation and ferroptosis. By providing sulfur for S0 biosynthesis, cysteine can support ferroptosis resistance independently of the canonical GPX4 pathway. Our results further suggest that hydropersulfides terminate radical chain reactions through the formation and self-recombination of perthiyl radicals. The autocatalytic regeneration of hydropersulfides may explain why low micromolar concentrations of persulfides suffice to produce potent cytoprotective effects on a background of millimolar concentrations of glutathione. We propose that increased S0 biosynthesis is an adaptive cellular response to radical-driven lipid peroxidation, potentially representing a primordial radical protection system.

Authors: Uladzimir Barayeu, Danny Schilling, Mohammad Eid, Thamara Nishida Xavier da Silva, Lisa Schlicker, Nikolina Mitreska, Christopher Zapp, Frauke Gräter, Aubry K. Miller, Reinhard Kappl, Almut Schulze, José Pedro Friedmann Angeli, Tobias P. Dick

Date Published: 15th Sep 2022

Publication Type: Journal

A Conformational Transition of the D’D3 Domain primes von Willebrand Factor for Multimerization

Abstract (Expand)

Von Willebrand factor (VWF) is a multimeric plasma glycoprotein that is critically involved in hemostasis. Biosynthesis of long VWF concatemers in the endoplasmic reticulum and the (trans-)Golgi is … still not fully understood. We use the single-molecule force spectroscopy technique magnetic tweezers to analyze a previously hypothesized conformational change in the D’D3 domain crucial for VWF multimerization. We find that the interface formed by submodules C8-3, TIL3, and E3 wrapping around VWD3 can open and expose two buried cysteines, Cys1099 and Cys1142, that are vital for multimerization. By characterizing the conformational change at varying levels of force, we are able to quantify the kinetics of the transition and the stability of the interface. We find a pronounced destabilization of the interface upon lowering the pH from 7.4 to 6.2 and 5.5. This is consistent with initiation of the conformational change that enables VWF multimerization at the D’D3 domain by a decrease in pH in the trans-Golgi network and Weibel-Palade bodies. Furthermore, we find a stabilization of the interface in the presence of coagulation factor VIII (FVIII), providing evidence for a previously hypothesized binding site in submodule C8-3. Our findings highlight the critical role of the D’D3 domain in VWF biosynthesis and function and we anticipate our methodology to be applicable to study other, similar conformational changes in VWF and beyond.

Authors: Sophia Gruber, Achim Löf, Adina Hausch, Fabian Kutzki, Res Jöhr, Tobias Obser, Gesa König, Reinhard Schneppenheim, Camilo Aponte-Santamaría, Frauke Gräter, Maria A. Brehm, Martin Benoit, Jan Lipfert

Date Published: 2nd Jun 2022

Publication Type: Journal

Martini 3 coarse-grained force field for poly(para-phenylene ethynylene)s.

Abstract (Expand)

Poly(<i>para</i>-phenylene ethynylene)s, or short PPEs, are a class of conjugated and semi-flexible polymers with a strongly delocalized π electron system and increased chain stiffness. Due … to this, PPEs have a wide range of technological applications. Although the material properties of single-chains or mixtures of few PPE chains have been studied in detail, the properties of large assemblies remain to be fully explored. Here, we developed a coarse-grained model for PPEs with the Martini 3 force field to enable computational studies of PPEs in large-scale assembly. We used an optimization geometrical approach to take the shape of the π conjugated backbone into account and also applied an additional angular potential to tune the mechanical bending stiffness of the polymer. Our Martini 3 model reproduces key structural and thermodynamic observables of single PPE chains and mixtures, such as persistence length, density, packing and stacking. We show that chain entanglement increases with the expense of nematic ordering with growing PPE chain length. With the Martini 3 PPE model at hand, we are now able to cover large spatio-temporal scales and thereby to uncover key aspects for the structural organization of PPE bulk systems. The model is also predicted to be of high applicability to investigate out-of-equilibrium behavior of PPEs under mechanical force.

Authors: Matthias Brosz, Nicholas Michelarakis, Uwe H F Bunz, Camilo Aponte-Santamaría, Frauke Gräter

Date Published: 4th May 2022

Publication Type: Journal

Mechano-redox control of Mac-1 de-adhesion from ICAM-1 by protein disulfide isomerase promotes directional movement of neutrophils under flow

Abstract (Expand)

Macrophage-1 antigen or Mac-1 (CD11b/CD18, αMβ2) is a leukocyte integrin essential for firm adhesion of neutrophils, lymphocytes and monocytes against flow when recruited to the endothelium. To migrate … to the site of inflammation, leukocytes require coordinated adhesion and de-adhesion for directional movement. The vascular thiol isomerase, protein disulfide isomerase (PDI), was found by fluorescence microscopy to colocalize with high affinity Mac-1 at the trailing edge of stimulated neutrophils when adhered to ICAM-1 under fluid shear. From differential cysteine alkylation and mass spectrometry studies, PDI cleaves two allosteric disulfide bonds, C169-C176 and C224-C264, in the βI domain of the β2 subunit, and in mutagenesis and cell transfection studies, cleavage of the C224-C264 disulfide bond was shown to selectively control Mac-1 dis-engagement from ICAM-1 under fluid shear. Molecular dynamics simulations and binding of conformation-specific antibodies reveal that cleavage of the C224-C264 bond induces conformational change and mechanical stress in the βI domain that allosterically alters exposure of an αI domain epitope and shifts Mac-1 to a lower affinity state. From studies of neutrophil adherence to ICAM-1 under fluid shear, these molecular events promote neutrophil motility in the direction of flow at high shear stress. In summary, shear-dependent PDI cleavage of neutrophil Mac-1 C224-C264 disulfide bond triggers Mac-1 de-adherence from ICAM-1 at the trailing edge of the cell and enables directional movement of neutrophils during inflammation.

Authors: Alexander Dupuy, Camilo Aponte-Santamaría, Adva Yeheskel, Frauke Gräter, Philip J. Hogg, Freda H. Passam, Joyce Chiu

Date Published: 30th Mar 2022

Publication Type: Journal

ATP allosterically stabilizes integrin-linked kinase for efficient force generation

Abstract (Expand)

Focal adhesions link the actomyosin cytoskeleton to the extracellular matrix regulating cell adhesion, shape, and migration. Adhesions are dynamically assembled and disassembled in response to extrinsic … and intrinsic forces, but how the essential adhesion component intergrin-linked kinase (ILK) dynamically responds to mechanical force and what role ATP bound to this pseudokinase plays remains elusive. Here, we apply force-probe molecular dynamics simulations of human ILK:α-parvin coupled to traction force microscopy to explore ILK mechanotransducing functions. We identify two key saltbridge-forming arginines within the allosteric, ATP-dependent force-propagation network of ILK. Disrupting this network by mutation impedes parvin binding, focal adhesion stabilization, force generation, and thus migration. Under tension, ATP shifts the balance from rupture of the complex to protein unfolding, indicating that ATP increases the force threshold required for focal adhesion disassembly. Our study proposes a new role of ATP as an obligatory binding partner for structural and mechanical integrity of the pseudokinase ILK, ensuring efficient cellular force generation and migration.

Authors: Isabel Martin, Michele Nava, Sara Wickström, Frauke Gräter

Date Published: 8th Mar 2022

Publication Type: Journal

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