Raúl Padrón

• PhD.
• Professor (Full) at University of Massachusetts Chan Medical School

Cardiac β-myosin variants cause hypertrophic (HCM) or dilated (DCM) cardiomyopathy by disrupting sarcomere contraction and relaxation. The locations of variants on isolated myosin head structures predict contractility effects but not the prominent relaxation and energetic deficits that characterize HCM. During relaxation, pairs of myosins form inte...

Striated muscle contraction involves sliding of actin thin filaments along myosin thick filaments, controlled by calcium through thin filament activation. In relaxed muscle, the two heads of myosin interact with each other on the filament surface to form the interacting-heads motif (IHM). A key question is how both heads are released from the surfa...

Myosin II is the motor protein that enables muscle cells to contract and nonmuscle cells to move and change shape¹. The molecule has two identical heads attached to an elongated tail, and can exist in two conformations: 10S and 6S, named for their sedimentation coefficients2,3. The 6S conformation has an extended tail and assembles into polymeric f...

Super-relaxation is a state of muscle thick filaments in which ATP turnover by myosin is much slower than that of myosin II in solution. This inhibited state, in equilibrium with a faster (relaxed) state, is ubiquitous and thought to be fundamental to muscle function, acting as a mechanism for switching off energy-consuming myosin motors when they...

Pumping of the heart is powered by filaments of the motor protein myosin, which pull on actin filaments to generate cardiac contraction. In addition to myosin, the filaments contain cardiac myosin-binding protein C (cMyBP-C), which modulates contractility in response to physiological stimuli, and titin, which functions as a scaffold for filament as...

Myosin storage myopathy (MSM) is a rare skeletal muscle disorder caused by mutations in the slow muscle/β-cardiac myosin heavy chain (MHC) gene. MSM missense mutations frequently disrupt the tail’s stabilizing heptad repeat motif. Disease hallmarks include subsarcolemmal hyaline-like β-MHC aggregates, muscle weakness and, occasionally, cardiomyopat...

Pumping of the heart is powered by filaments of the motor protein myosin that pull on actin filaments to generate cardiac contraction. In addition to myosin, the filaments contain cardiac myosin-binding protein C (cMyBP-C), which modulates contractility in response to physiological stimuli, and titin, which functions as a scaffold for filament asse...

Under relaxing conditions, the two heads of myosin II interact with each other and with the proximal part (S2) of the myosin tail, establishing the interacting-heads motif (IHM), found in myosin molecules and thick filaments of muscle and nonmuscle cells. The IHM is normally thought of as a single, unique structure, but there are several variants....

Electron microscopy shows that myosin heads in thick filaments isolated from striated muscles interact with each other and with the myosin tail under relaxing conditions. This “interacting-heads motif” (IHM) is highly conserved across the animal kingdom and is thought to be the basis of the super-relaxed state. However, a recent X-ray modeling stud...

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Myosin molecules in the relaxed thick filaments of striated muscle have a helical arrangement in which the heads of each molecule interact with each other, forming the interacting-heads motif (IHM). In relaxed mammalian skeletal muscle, this helical ordering occurs only at temperatures >20°C and is disrupted when temperature is decreased. Recent x-...

BACKGROUND: Hypertrophic cardiomyopathy (HCM) is caused by pathogenic variants in sarcomere protein genes that evoke hypercontractility, poor relaxation, and increased energy consumption by the heart and increased patient risks for arrhythmias and heart failure. Recent studies show that pathogenic missense variants in myosin, the molecular motor of...

Thick filaments from some striated muscles are regulated by phosphorylation of myosin regulatory light chains (RLCs). A tarantula thick filament quasi-atomic model achieved by cryo-electron microscopy has advanced our understanding on how this regulation occurs. In native thick filaments, an asymmetric intramolecular interaction between the actin-b...

Significance All animals have the ability to move. Myosin II is the motor protein that generates this movement by powering muscular contraction; it also drives motility in nonmuscle cells. In relaxed muscle and in quiescent nonmuscle cells, myosin II is switched off by intramolecular interactions between its heads that inhibit its activity. This in...

Tarantula’s leg muscle thick filament is the ideal model for the study of the structure and function of skeletal muscle thick filaments. Its analysis has given rise to a series of structural and functional studies, leading, among other things, to the discovery of the myosin interacting-heads motif (IHM). Further electron microscopy (EM) studies hav...

The tarantula skeletal muscle X-ray diffraction pattern suggested that the myosin heads were helically arranged on the thick filaments. Electron microscopy (EM) of negatively stained relaxed tarantula thick filaments revealed four helices of heads allowing a helical 3D reconstruction. Due to its low resolution (5.0 nm), the unambiguous interpretati...

Domains of human β-cardiac myosin. DOI: http://dx.doi.org/10.7554/eLife.24634.029

DCM-causing variants cluster in distinct regions of MYH7 from HCM-causing variants. DOI: http://dx.doi.org/10.7554/eLife.24634.032

Intra- and inter-molecular interactions sequences involved in human β-cardiac myosin interacting-heads motif (IHM) PDB 5TBY. DOI: http://dx.doi.org/10.7554/eLife.24634.030

Variants Clustered on the Myosin Mesa. DOI: http://dx.doi.org/10.7554/eLife.24634.033

HCM variants cluster on residues involved in IHM-related inter- and intra-molecular interactions. DOI: http://dx.doi.org/10.7554/eLife.24634.031

Comparison of prevalence of rare (ExAC global AF <1×10−4) missense variants in MYH7 in 6112 HCM cases and ExAC controls. DOI: http://dx.doi.org/10.7554/eLife.24634.034

Leveraging regional distribution for the clinical interpretation of DCM-causing variants. DOI: http://dx.doi.org/10.7554/eLife.24634.035

Tarantula striated muscle is an outstanding system for understanding the molecular organization of myosin filaments. 3D reconstruction based on cryo-EM images and single-particle image processing revealed that in a relaxed state, myosin molecules undergo intramolecular head–head interactions, explaining why head activity switches off. The filament...

Significance All animals have the ability to move. In most animals, striated muscles move the body and smooth muscles the internal organs. In both muscles, contraction results from interaction between myosin and actin filaments. Based on vertebrate studies, smooth and striated muscles are thought to have different protein components and filament st...

Molecular dynamics simulations of smooth and striated muscle myosin regulatory light chain (RLC) N-terminal extension (NTE) showed that diphosphorylation induces a disorder-to-order transition. Our goal here was to further explore the effects of mono- and diphosphorylation on the straightening and rigidification of the tarantula myosin RLC NTE. For...

Phosphorylation of myosin regulatory light chain (RLC) N-terminal extension (NTE) activates myosin in thick filaments. RLC phosphorylation plays a primary regulatory role in smooth muscle and a secondary (modulatory) role in striated muscle, which is regulated by Ca2+ via TnC/TM on the thin filament. Tarantula striated muscle exhibits both regulato...

Se presenta un resumen de las actividades de la expedición realizada entre el 12 y 15 de abril de 2015 a la zona del Catatumbo, en el Sur de la Cuenca del Lago de Maracaibo (CLM). En esta actividad participaron 14 expedicionarios, pertenecientes al Centro de Modelado Científico (CMC) de la Universidad del Zulia, al Servicio de Meteorología de la Av...

Electron microscopic studies have shown that the inhibited (relaxed) state of myosin II is characterized by an intramolecular interaction between myosin heads, in both thick filaments and isolated monomers. Interaction inhibits head activity by blocking actin-binding in one head and ATPase activity in the other. Interacting-heads are present in ver...

All striated muscles are formed by sarcomeres of interdigitated thick and thin filaments, and are activated by an increase in intracellular Ca 2+ , leading to actin-myosin interaction, filament sliding, and contraction. In most muscles, Ca 2+ -regulation is achieved through the Ca 2+ -sensitive troponin-tropomyosin switch on the thin filaments, whi...

Myosin interacting-heads (MIH) motifs are visualized in 3D-reconstructions of thick filaments from striated muscle. These reconstructions are calculated by averaging methods using images from electron micrographs of grids prepared using numerous filament preparations. Here we propose an alternative method to calculate the 3D-reconstruction of a sin...

Schistosomes are parasitic worms infecting 200 million humans worldwide. Schistosomiasis is treated with the drug praziquantel, which affects the parasite muscle, possibly by binding to myosin light chains. To understand the molecular functioning of Schistosome muscles, we have studied their cellular and molecular makeup. EM sections of adult worms...

Chapter 38 Raúl Padrón "Two and a half years at the LMB that imprinted my scientific career (1980-83) Pages 315 -322

Myosin filaments from many muscles are activated by phosphorylation of their regulatory light chains (RLCs). Structural analysis of relaxed tarantula thick filaments shows that the RLCs of the interacting free and blocked myosin heads are in different environments. This and other data suggested a phosphorylation mechanism in which Ser-35 of the fre...

RE PORT OF A NEW MUTATION (Val748Leu) ASSOCIATED WITH HYPERTROPHIC MIOCARDIOPATHY LOCATED IN THE C5 DOMAIN OF THE CARDIAC MYOSIN BINDING PROTEIN-C (cMyBP-C) Hypertophic miocardiopathy (HMC) is a primary hearth disease mainly characterized by left ventricle hypertrophy, its most serious consequence being sudden death. It has been associated to sarc...

Hypertophic miocardiopathy (HMC) is a primary hearth disease mainly characterized by left ventricle hypertrophy, its most serious consequence being sudden death. It has been associated to sarcomeric protein mutations, cardiac β-myosin and the cardiac myosin binding protein-C (cMyBP-C) being the most affected. Since until now, only clinical diagnost...

Electron microscopy (EM) studies of 2D crystals of smooth muscle myosin molecules have shown that in the inactive state the two heads of a myosin molecule interact asymmetrically forming a myosin interacting-heads motif. This suggested that inactivation of the two heads occurs by blocking of the actin-binding site of one (free head) and the ATP hyd...

The UM-IVIC (Meteorology Unit, Venezuelan Institute for Scientific Research) was created in late 2010 in direct evolution of virtual Meteorology Center (CvM by his acronym in Spanish) to support Caribbean and Venezuela research in meteorology.

Myosin filaments from many muscles are activated by phosphorylation of their regulatory light chains (RLCs). To elucidate the structural mechanism of activation, we have studied RLC phosphorylation in tarantula thick filaments, whose high-resolution structure is known. In the relaxed state, tarantula RLCs are ~50% non-phosphorylated and 50% mono-ph...

Myosin-binding protein C (MyBP-C) is a thick filament protein playing an essential role in muscle contraction, and MyBP-C mutations cause heart and skeletal muscle disease in millions worldwide. Despite its discovery 40 y ago, the mechanism of MyBP-C function remains unknown. In vitro studies suggest that MyBP-C could regulate contraction in a uniq...

The registration of volumetric structures in real space involves geometric and density transformations that align a target map and a probe map in the best way possible. Many computational docking strategies exist for finding the geometric transformations that superimpose maps, but the problem of finding an optimal density transformation, for the pu...

Familial hypertrophic cardiomyopathy is a primary myocardial autosomal dominant disease, characterized by increased left ventricular mass and wall thickness in the absence of a pressure overload or metabolic stimulus. This disease affect to people of all ages, being the sudden death its principal consequence. FHC is genetically heterogeneous and ca...

Muscle contraction involves the interaction of the myosin heads of the thick filaments with actin subunits of the thin filaments. Relaxation occurs when this interaction is blocked by molecular switches on these filaments. In many muscles, myosin-linked regulation involves phosphorylation of the myosin regulatory light chains (RLCs). Electron micro...

Myosin binding protein C (MyBP-C) is a component of the thick filament of striated muscle. The importance of this protein is revealed by recent evidence that mutations in the cardiac gene are a major cause of familial hypertrophic cardiomyopathy. Here we investigate the distribution of MyBP-C in the A-bands of cardiac and skeletal muscles and compa...

Blebbistatin is a small-molecule, high-affinity, noncompetitive inhibitor of myosin II. We have used negative staining electron microscopy to study the effects of blebbistatin on the organization of the myosin heads on muscle thick filaments. Loss of ADP and Pi from the heads causes thick filaments to lose their helical ordering. In the presence of...

The structure of the thick filaments of striated muscle has been finally understood at the molecular level. The structure reveals intra- and inter-molecular interactions that held the myosin heads forming helices on the thick filament surface. The phosphorylation of the myosin regulatory light chains induces the weakening of these interactions, all...

The structure of the thick filaments of striated muscle has been finally understood at the molecular level. The structure reveals intra- and inter-molecular interactions that held the myosin heads forming helices on the thick filament surface. The phosphorylation of the myosin regulatory light chains induces the weakening of these interactions, all...

Contraction of muscle involves the cyclic interaction of myosin heads on the thick filaments with actin subunits in the thin filaments. Muscles relax when this interaction is blocked by molecular switches on either or both filaments. Insight into the relaxed (switched OFF) structure of myosin has come from electron microscopic studies of smooth mus...

Myosin heads are helically ordered on the thick filament surface in relaxed muscle. In mammalian and avian filaments this helical arrangement is dependent on temperature and it has been suggested that helical order is related to ATP hydrolysis by the heads. To test this hypothesis, we have used electron microscopy and image analysis to study the ab...

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease, which may afflict as many as 1 in 500 subjects (0.2%), being probably the most common hereditary cardiovascular disease and the most common cause of sudden cardiac death (SCD). Hypertrophic cardiomyopathy is characterized by the presence of unexplained left ventricular hypertrophy...

The sliding of thick filaments along thin filaments is produced by the active shortening of the striated muscle during contraction, and is controlled by molecular switches in the thin and/or thick filaments. In spite of advances on the elucidation of the molecular mechanism of actin-linked regulation, the myosin-linked regulation mechanism has been...

The vertebrate striated muscle Z-band connects actin filaments of opposite polarity from adjacent sarcomeres and allows tension to be transmitted along a myofibril during contraction. Z-bands in different muscles have a modular structure formed by layers of alpha-actinin molecules cross-linking actin filaments. Successive layers occur at 19 nm inte...

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Analysis of the structure and function of native thick (myosin-containing) filaments of muscle has been hampered in the past by the difficulty of obtaining a pure preparation. We have developed a simple method for purifying native myosin filaments from muscle filament suspensions. The method involves severing thin (actin-containing) filaments into...

Analysis of the structure and function of native thick filaments of muscle has been hampered in the past by the difficulty of obtaining a pure preparation. While such preparations have been obtained (Morimoto and Harrington, 1973. J. Mol. Biol. 77:165-175; Trinick, 1982. Meth. Enzymol. 85:17-20), they have involved specialized centrifugation approa...

Analysis of the structure and function of native thick filaments of muscle has been hampered in the past by the difficulty of obtaining a pure preparation. Although such preparations have been obtained, they have involved specialized centrifugation approaches in addition that the native helical filament structure is not preserved. Therefore, we hav...

Contraction is modulated in many striated muscles by Ca2+-calmodulin dependent phosphorylation of the myosin regulatory light chain (RLC) by myosin light chain kinase. We have investigated the biochemical mechanism of RLC phosphorylation in tarantula muscle to better understand the basis of myosin-linked regulation. In an earlier study it was concl...

Three-dimensional reconstructions of the negatively stained thick filaments of tarantula muscle with a resolution of 50 Å have previously suggested that the helical tracks of myosin heads are zigzagged, short diagonal ridges being connected by nearly axial links. However, surface views of lower contour levels reveal an additional J-shaped feature a...