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The autosomal dominant striated muscle disease myoglobinopathy is due to the single point mutation His98Tyr in human myoglobin (MB) [Olive et al. (2019) Nat Comm 10, 1396], the heme protein responsible for binding, storage, and controlled release of O2 in striated muscle. In order to understand the molecular basis of this disease, a comprehensive biochemical and biophysical study on wt MB and the variant H98Y has been performed. Although only small differences exist between the active site architectures of the two proteins, the mutant (a) exhibits an increased reactivity toward hydrogen peroxide, (b) exhibits a higher tendency to form high-molecular-weight aggregates, and (c) is more prone to heme bleaching, possibly as a consequence of the observed H2 O2 -induced formation of the Tyr98 radical close to the metal center. These effects add to the impaired oxygen binding capacity and faster heme dissociation of the H98Y variant compared with wt MB. As the above effects result from bond formation/cleavage events occurring at the distal and proximal heme sites, it appears that the molecular determinants of the disease are localized there. These findings set the basis for clarifying the onset of the cascade of chemical events that are responsible for the pathological symptoms of myoglobinopathy.

Cofilins are small protein of the actin depolymerizing family. Actin polymerization/depolymerization is central to a number of critical cellular physiological tasks making cofilin a key protein for several physiological functions of the cell. Cofilin activity is mainly regulated by phosphorylation on serine residue 3 making this post-translational modification key to the regulation of myofilament integrity. In fact, in this form, the protein segregates in myocardial aggregates in human idiopathic dilated cardiomyopathy. Since myofilament network is an early target of oxidative stress we investigated the molecular changes induced by oxidation on cofilin isoforms and their interplay with the protein phosphorylation state to get insight on whether/how those changes may predispose to early protein aggregation. Using different and complementary approaches we characterized the aggregation properties of cofilin-2 and its phosphomimetic variant (S3D) in response to oxidative stress in silico, in vitro and on isolated cardiomyocytes. We found that the phosphorylated (inactive) form of cofilin-2 is mechanistically linked to the formation of an extended network of fibrillar structures induced by oxidative stress via the formation of a disulfide bond between Cys39 and Cys80. Such phosphorylation-dependent effect is likely controlled by changes in the hydrogen bonding network involving Cys39. We found that the sulfide ion inhibits the formation of such structures. This might represent the mechanism for the protective effect of the therapeutic agent Na2S on ischemic injury., Graphical abstract Image 1, Highlights • Cofilin changes the hydrogen bonding network involving Cys39 in its phosphorylated form. • This phosphorylation-dependent effect of oxidation promotes the formation of a disulfide bond between Cys39 and Cys80. • The formation of the Cys39 and Cys80 disulfide bond favors the formation of fibrillar aggregates. • The sulfide ion inhibits the formation of such structures.

The reported data are related to a research paper entitled "Phosphorylated cofilin-2 is more prone to oxidative modifications on Cys39 and favors amyloid fibril formation" [1] . Info about the formation and redox properties of the disulfide bridge of a protein is quite difficult to obtain and only in a few cases was it possible to observe a cyclic voltammetry (CV) signal [ 2 , 3 ]. Human cofilin-2 contains two cysteines (Cys39 and Cys80) which can be oxidized in suitable conditions and form a disulfide bridge [1] . For this purpose, CV measurements were carried out on human cofilin-2 WT and its mutant S3D immobilized on a gold electrode coated by an anionic self-assembled monolayer (SAM), after a pre-oxidation time which was fundamental for observing a CV signal relating to the oxidation/reduction process of the disulfide bridge of the proteins. The data include CV curves obtained with and without electrochemical pre-oxidation and after oxidation with H2O2. In addition, the plot of the cathodic peak current vs. electrochemical pre-oxidation time and the pH dependence of the formal potential (E°’) are reported. The data obtained by CV measurements were used to determine the time required to form the disulfide bridge for the immobilized proteins and, consequently, to observe the CV signal, to calculate the E°’ values and analyse the pH dependence of E°’. The electrochemical data were provided which will be useful for further electrochemical investigations regarding proteins bearing disulfide bridge(s) or cysteines prone to oxidation.

Myoglobin, encoded by MB, is a small cytoplasmic globular hemoprotein highly expressed in cardiac myocytes and oxidative skeletal myofibers. Myoglobin binds O-2, facilitates its intracellular transport and serves as a controller of nitric oxide and reactive oxygen species. Here, we identify a recurrent c.292C>T ( p.His98Tyr) substitution in MB in fourteen members of six European families suffering from an autosomal dominant progressive myopathy with highly characteristic sarcoplasmic inclusions in skeletal and cardiac muscle. Myoglobinopathy manifests in adulthood with proximal and axial weakness that progresses to involve distal muscles and causes respiratory and cardiac failure. Biochemical characterization reveals that the mutant myoglobin has altered O-2 binding, exhibits a faster heme dissociation rate and has a lower reduction potential compared to wild-type myoglobin. Preliminary studies show that mutant myoglobin may result in elevated superoxide levels at the cellular level. These data define a recognizable muscle disease associated with MB mutation., We thank the patients and their families for their collaboration. This study has been funded by Instituto de Salud Carlos III through the project PI14/00738 (co-funded by European Regional Development Fund. ERDF, a way to build Europe) and from a grant from Genzyme Foundation to MO. We thank CERCA Programme/Generalitat de Catalunya for institutional support. GR, NGL, and ARRF are supported by Australian National Health and Medical Research Council Fellowships APP1002147, APP1035955, APP1154524, and Project Grants APP1080587 and APP1146321. ARRF was also supported by a Senior Research Fellowship from the Cancer Research Trust, the MACA Ride to Conquer Cancer and an Australian Research Council Discovery Project Grant (DP160101960). MC is supported by ISCIII (JR15/00042). AWr is a Ragnar Soderberg Fellow in Medicine (M77/13) and is supported by the Swedish Research Council (AW (VR2016-02179). AWe is supported by the Swedish Research Council (2016-01082), Stockholm County Council (20170022), the Swedish Brain Foundation (FO2015-0146), and the Knut & Alice Wallenberg Foundation (KAW 2013.0026 and KAW 2014.0293). KGC is supported by the KOOR, UZ Leuven, Belgium. AG is supported by the Research Council KU Leuven (C24/16/045). JK is a recipient of the Royal Society Wolfson Research Merit Award. TS is supported by Stockholm County Council (20170831), Stiftelsen Frimurare Foundation, and Promobilia. LH is supported by an Australian National Health and Medical Research Council Fellowship (APP1117366). HV is supported by a National Heart Foundation of Australia Fellowship (101930). mu FTIR microscope analysis was performed at MIRAS beamline at ALBA Synchrotron with the collaboration of ALBA staff. We thank professor Josep Garcia Valero from the University of Barcelona for helpful comments on the ultrastructural features. We thank Dolores Moreno, Susana Arnedo, Guy Brochier, and Benjamin Torrejon-Escribano for excellent technical assistance and to the Audiovisual Department from Hospital Universitari de Bellvitge for their help with the preparation of the figures. KCG wants to thank Klara Mallants for technical support and to Dr. Sjoerd G. van Duinen (Leiden), and professsor Joachim Weis (Aachen). Muscle sample and associated data from Family 5 were obtained from Cardiobiotec Biobank (CRB-HCL Hospices Civils de Lyon BB-0033-00046).

OBJECTIVE: Congenital myopathies are typically characterised by early onset hypotonia, weakness and hallmark features on biopsy. Despite the rapid pace of gene discovery, approximately 50% of patients with a congenital myopathy remain without a genetic diagnosis following screening of known disease genes. METHODS: We performed exome sequencing on two consanguineous probands diagnosed with a congenital myopathy and muscle biopsy showing selective atrophy/hypotrophy or absence of type II myofibres. RESULTS: We identified variants in the gene (MYL1) encoding the skeletal muscle fast-twitch specific myosin essential light chain in both probands. A homozygous essential splice acceptor variant (c.479-2A>G, predicted to result in skipping of exon 5 was identified in Proband 1, and a homozygous missense substitution (c.488T>G, p.(Met163Arg)) was identified in Proband 2. Protein modeling of the p.(Met163Arg) substitution predicted it might impede intermolecular interactions that facilitate binding to the IQ domain of myosin heavy chain, thus likely impacting on the structure and functioning of the myosin motor. MYL1 was markedly reduced in skeletal muscle from both probands, suggesting that the missense substitution likely results in an unstable protein. Knock down of myl1 in zebrafish resulted in abnormal morphology, disrupted muscle structure and impaired touch-evoked escape responses, thus confirming that skeletal muscle fast-twitch specific myosin essential light chain is critical for myofibre development and function. INTERPRETATION: Our data implicate MYL1 as a crucial protein for adequate skeletal muscle function and that MYL1 deficiency is associated with a severe congenital myopathy.

Scientific Reports 6: Article number: 35865; published online: 24 October 2016; updated: 19 January 2017. The Author Contributions statement in this Article is incomplete: F.B., D.M., M.P., L.L., F.d.M. and E.C. acquired and analyzed the data; C.A.B., G.D.R., M.F.B. and M.B. provided critical input to the analyzed data and to the manuscript; R.

Neuroglobin (Ngb) was the first vertebrate nerve globin to be identified. Since then, different physiological roles have been hypothesised for this hexa-coordinated globin, but its function is far from being unambiguously assigned. In a previous work, we collected first evidences of Ngb potentially taking part to electron transfer (ET) processes in vivo, investigating the redox thermodynamics of this globin. Here, we perform a computational investigation on the complex between Ngb and its putative in vivo partner cyt c and on the ET process between the two species. The simulated structure of the complex is amenable for ET in terms of distance and relative protein orientation. Moreover, the redox-dependent stability of the predicted Ngb-cyt c adduct and the very good agreement between calculated determinants to the ET rate and those of paradigmatic metalloproteins acting as electron shuttles all support a potential role of neuroglobin as an electron transfer species.

Evolutionarily widespread, functionally and structurally diverse and still largely unexplored, Kelch proteins, characterized by the presence of a conserved C-terminal beta-propeller, are implicated in a number of diverse fundamental biological functions, including cytoskeletal arrangement, regulation of cell morphology and organization, and protein degradation. Mutations in the genes encoding for Kelch superfamily members are being discovered as the cause of several neuromuscular diseases and cancer. The E528K mutation in Kelch protein KLHL40, which regulates skeletal muscle myogenesis, has been identified as a frequent cause of severe autosomal-recessive nemaline myopathy (NM). We use all-atom molecular dynamics simulations to characterize the dynamic behaviour of the beta-propeller of the wild-type protein and identify correlated motions underlying the in vivo functionality. We also modelled the NM-associated mutation and we found that it does not lead to dramatic disruption of the beta-propeller architecture; yet, residue 528 is a hub in the correlated motions of the domain, and mutation-induced local structural alterations are propagated to the whole protein, affecting its dynamics and physicochemical properties, which are fundamental for in vivo interaction with partners. Our results indicate that rational design of drugs can be envisioned as a strategy for restoring the internal network of communication and resetting KLHL40 to its physiological state.

In this paper, the direct one-dimensional beam model introduced by one of the authors is refined to take into account nonsymmetrical beam cross-sections. Two different beam axes are considered, and the strain is described with respect to both. Two inner constraints are assumed: a vanishing shearing strain between the cross-section and one of the two axes, and a linear relationship between the warping and twisting of the cross-section. Considering a grade one mechanical theory and nonlinear hyperelastic constitutive relations, the balance of power, and standard localization and static perturbation procedures lead to field equations suitable to describe the flexural-torsional buckling. Some examples are given to determine the critical load for initially compressed beams and to evaluate their post-buckling behavior.

A direct one-dimensional beam model is adopted. Kinematics is described by axis displacement, rigid rotation of the cross-section and an average measure of warping. Mechanical power is introduced as a linear functional of the kinematic descriptors and their first derivatives, hence mechanical actions naturally result as their duals. In particular, the bi-shear and bi-moment turn out to be quantities spending power on the warping and on its first derivative, respectively. Assuming as basic postulate the balance between external and internal power, local equilibrium equations for the mechanical actions are obtained. In addition to the standard inner constraint of shear indeformability, a linear relationship between twist and warping is assumed. To obtain field equations in terms of displacements, non-linear hyperelastic constitutive relations are formulated. Two coupled bifurcations for axially loaded beams are examined: in the first case no coupling occurs, in the second the beam can be sensitive to initial imperfections.

International audience; Interactive buckling of an elastically restrained truss structure is investigated by using an improved version of the Byskov-Hutchinson perturbation analysis. The mechanical model consists of two horizontal beams connected by rigid diagonals, whose out-of-plane displacements are prevented by a continuous distribution of linear springs. When the two horizontal beams are compressed, three buckling modes are possible: one overall in-plane mode and two local (lateral and torsional) modes which, for a particular choice of the geometry of the structure, may occur nearly simultaneously. Three nonlinear equilibrium equations are derived in the amplitudes of the three buckling modes and solved numerically for given initial imperfections.

The objective of this paper was solving the optimization problem of lightweight stiffened structures modelled as a two-dimensional domain in an efficient computational way. The underlying premise was that mass should be distributed in an efficient way, so as to use a minimum amount of material to accomplish the mechanical function. This premise was expressed as a global, multi-objective optimization problem in which stiffness and mass were conflicting objectives. Alternative local evolution rules were implemented to update mass density or Young's modulus at each step of the iterative procedure. The solution of the structural optimization problem was accomplished by a novel automatic procedure consisting of two consecutive stages of control and optimization. In the first stage of Proportional Integral Derivative (PID) control gains were manually selected whereas in the second stage the finding of optimal values of control gains, target, and cost indices was allowed. In this study a bone-like material was adopted and a thin slab was analysed as a sample problem.

We present the effect of warping constraints on the buckling of a thin-walled two-bar (‘Roorda’) plane frame subjected to a ‘dead’ load at the joint. The hinges with the ‘ground’ allow rotation with axis perpendicular to the frame plane; the joint is constrained in the same direction to simulate a 3D-frame. Warping constraints are considered; the restraint at the joint is first supposed rigid and fixed, then is supposed linear elastic to account for different lateral restraint. Critical loads are evaluated numerically; an analysis of the post-buckling behaviour will be part of future investigations.

We present two applications of a direct one-dimensional beam model suitable for describing the buckling of thin-walled structures. The first application considers the buckling of a compressed beam with an intermediate stiffener under various warping constraints. The second describes the buckling of a two-bar frame, known as a Roorda frame, loaded by a dead force at the joint. Various warping constraints at the bar ends are considered and the relevant buckling modes and loads are numerically evaluated. Numerical results are presented for both cases; some of these appear to be new.

The three-dimensional free vibrations of an orbiter-towed tethered satellite system with nominally vertical tether during stationkeeping phase are studied analytically. The tether is modeled as an elastic continuum with mass and the orbiter and the subsatellite as two concentrated masses. The linearized equations of motion with variable coefficients are solved by means of a perturbation technique. An analysis of the order of magnitude of the different terms involved permits evaluation of the coupling between longitudinal and transversal in-plane vibrations coming to an approximate closed-form solution of the eigenvalue problem.

A beam model aimed at describing the flexural–torsional buckling of thin-walled members with non-symmetric cross-sections is presented. Two beam axes are introduced, and strain is defined with respect to both. The shearing strain between the cross-section and one of the two axes is assumed to vanish; the warping is supposed to be linear in the twist. Non-linear hyperelastic constitutive relations are introduced; by means of standard localization and static perturbation techniques, the field equations describing the flexural–torsional buckling are obtained. One benchmark example is given and some numerical values of the critical load for various warping constraints at the beam ends are provided.

Liapunov theory is first presented and discrete mechanical systems are in particular analysed. Then buckling and postbuckling analysis of continuous mechanical system using the general theory formulated by Koiter are discussed in some detail following Budiansky presentation. Finally, the influence of multiple interactive buckling modes on postbuckling behaviour is analysed in some detail for frames, thin-walled members and panels.

Mathematical Modelling of Instability Phenomena.- Phenomenological Modelling of Instability.- Modelling Buckling Interaction.- Computational asymptotic post-buckling analysis of slender elastic structures.- Mechanical Models for the Subclasses of Catastrophes.

In this paper, the effect of the interaction between one overall buckling mode and many local modes on the post-buckling behaviour of uniformly compressed corrugated sheets is analysed by means of the general theory of elastic stability. The analysis is restricted to third order terms of the energy expansion and, therefore, it can be fruitfully applied to the investigation of structures with asymmetric post-buckling behaviour only. Initial imperfection effect is taken into account. By using the finite strip method, an extensive parametric analysis is performed.

The modified potential energy approach to the nonlinear analysis of slender elastic beams is employed to investigate the buckling and postbuckling behavior of two symmetric plane frames, namely a hinged portal frame and a hinged two-bar frame, The beams are assumed to be inextensible and shear undeformable. The “hybrid” functional on which the present analysis is based according to a Koiter-type energy approach is obtained from the total potential energy functional by adding extra terms which account for the nonlinear energy associated with the internal forces applied at the beam ends. Thus the nonlinear constraints on the potential energy (expressed in terms of the cross-section rotation φ only), which are associated with the continuity condition relative to the axial and lateral displacement across the joints, are accounted for by introducing the corresponding joint forces as Lagrangian multipliers. The inherent simplicity of the proposed beam model facilitates the postbuckling analysis of the ...

ABSTRACT The modified potential energy approach of flexurally elastic, axially, and shear undeformable beams is employed to investigate the buckling and (asymmetric) postbuckling behavior of the two-bar frame which was experimentally tested by Roorda in 1965. Following a Koiter-type energy approach, a suitable perturbation formulation is, derived from a hybrid functional which is obtained by adding to the potential energy certain extra terms which account for the energy associated with the internal joint forces acting on the beam. In this way the nonlinear constraints expressing continuity of displacement across the joints are accommodated by introducing joint forces acting as Lagrangian multipliers. The inherent simplicity of the model herein proposed allows a thorough parametric analysis to be performed without undue complications up to and including fourth-order terms. The general trend compares favorably with the experimental results. Previous analytical results limited to a third-order analy...

The postbuckling behavior of a one-bay, two-storey frame with built-in edges and symmetric with respect to midspan is analyzed. Columns are assumed to be inextensible and shear-undeformable, and beams are rigid. Then two buckling modes are possible, that is, sidesway of the lower floor with rigid horizontal displacement of the top floor and sidesway of the top floor with the lower floor undergoing no displacement. Obviously, the two buckling modes occur simultaneously if the ratios EI/h7 (EI being the bending stiffness of a column and h its length) are properly selected. Within the framework of a Koiter-type energy approach a suitable perturbation formulation is derived from a “hybrid” functional which is obtained by adding to the potential energy certain extra terms which account for the nonlinear energy associated with the internal forces applied to the beam at the joints. Results show that the postbuckling behavior of a single buckling mode can be stable or unstable according to the value of t...

In this paper, the effect of boundary conditions on multiple interactive buckling in thin-walled members under compression is analyzed by means of the general theory of stability. The total potential energy is expanded to up to third-order terms to investigate structures with asymmetric postbuckling behavior; initial geometric imperfections are taken into account. Under simplifying assumptions, the nonlinear equations governing the postcritical behavior reduce to a linear eigenvalue problem that is independent of the geometric and mechanical properties of the column and depends on the boundary conditions only. Localization of the buckling patterns is verified when a large number of local buckling modes occur simultaneously. A continuum representation, based on the substitution of the algebraic eigenvalue problem with a differential equation, is proposed.

In two previous works the effect of simultaneous overall buckling modes on post-buckling behaviour of a one-bay-two-storey frame with rigid beams, flexible columns and fixed edges has been analysed on the basis of the nonlinear theory of elastic stability developed by Koiter. In the present article interaction effect of simultaneous overall and local buckling in a simple portal frame with the same boundary condition described by the same beam model is investigated. Far from being conclusive, results so far obtained show that imperfection sensitivity in the presence of local and overall buckling is higher in comparison with the previous case.

International audience; On the basis of the general theory of elastic stability due to Koiter, postbuckling analysis of simply supported channels under uniform compression is performed. Attention is essentially focused on local/eularian and local/flexural-torsional simultaneous bucklin modes interaction. The column is treated as a plate assemblage. Linearized expressions for the displacement field are employed while assuming strain-displacements relationships that are linear for the curvatures and up to second order terms for the in-plane strains. The total potential energy is hence written up to third order terms in order to investigate asymmetric buckling phenomena. A discrete model is developed through an automatic procedure of algebraic manipulation, and an extensive parametric analysis is performed. After determining the range of geometric parameters which characterize different types of interaction, it is found that in the postbuckling range the local/eulerian interaction is more dangerous than the local/flexural-torsional one, due to the column higher imperfection sensitivity.

In this paper the bifurcation analysis of a circular arch under hydrostatic pressure in the elastic postbuckling range is performed by means of a geometrically exact beam model. The relevant nonlinear field equations are solved by utilizing a perturbation technique. A number of numerical results regarding the dependence of the critical load and the second order load parameter on the geometric and mechanical parameters are plotted in diagrams.

International audience; An analytical model is presented to study the three-dimensional free vibrations of the Tethered Satellite System. In the model, the tether is considered as an elastic continuum with mass, while the Space Shuttle and the subsatellite are considered as two concentrated masses. Linearized equations of motion are given for out-of-plane and in-plane vibrations. Extended numerical analyses are performed for the geometrical and mechanical properties of the system. It is found that the two in-plane motion components are weakly coupled through the gyroscopic forces, with generally transversal or longitudinal type modes. The transversal modes are almost identical to the out-of-planes modes.

International audience; In this paper the effect of the interaction between two or more simultaneous buckling modes on the postbuckling behaviour of uniformly compressed thin-walled members (TWM) is analysed by means of the general theory of elastic stability. The analysis is restricted to third-order terms of the energy expansion and therefore can be fruitfully applied to the investigation of structures with asymmetric postbuckling behaviour only. Initial imperfection effect is taken into account. A simplified procedure is suggested for solving the nonlinear equations relative to the evaluation of the bifurcated paths. By using the finite strip method an extensive parametric analysis is performed. It is found that when the flexural-torsional (FT) buckling interacts with a local symmetric and antisymmetric mode, sensitivity to initial inperfections is remarkable and is comparable to the one arising from the interaction between the Euler (E) and any local buckling.

The buckling and post-buckling analysis of elastic planar frames is considered and the use of geometrically exact beam models is thereby advocated. It is shown that usual technical beam models fail to predict correctly the curvature of the post-buckling curve at bifurcation even for standard problems of elastic stability theory. It is also argued that versatile and efficient computational procedures for bifurcation analysis of general planar frames are to be based on unconstrained beam models. Some remarks on finite element representation of nonlinear beam models are passed in conclusion.