Myosin II isoforms in smooth muscle: heterogeneity and function

2007 ◽  
Vol 293 (2) ◽  
pp. C493-C508 ◽  
Author(s):  
Thomas J. Eddinger ◽  
Daniel P. Meer
Keyword(s):  
Smooth Muscle ◽  
Conformational Changes ◽  
Atp Hydrolysis ◽  
Expression Profiles ◽  
Myosin Ii ◽  
Thick Filament ◽  
Actin Binding ◽  
Head Region ◽  
Organ Systems ◽  
Species Specific

Both smooth muscle (SM) and nonmuscle class II myosin molecules are expressed in SM tissues comprising hollow organ systems. Individual SM cells may express one or more of multiple myosin II isoforms that differ in myosin heavy chain (MHC) and myosin light chain (MLC) subunits. Although much has been learned, the expression profiles, organization within contractile filaments, localization within cells, and precise roles in various contractile functions of these different myosin molecules are still not well understood. However, data supporting unique physiological roles for certain isoforms continues to build. Isoform differences located in the S1 head region of the MHC can alter actin binding and rates of ATP hydrolysis. Differences located in the MHC tail can alter the formation, stability, and size of the myosin thick filament. In these distinct ways, both head and tail isoform differences can alter force generation and muscle shortening velocities. The MLCs that are associated with the lever arm of the S1 head can affect the flexibility and range of motion of this domain and possibly the motion of the S2 and motor domains. Phosphorylation of MLC20 has been associated with conformational changes in the S1 and/or S2 fragments regulating enzymatic activity of the entire myosin molecule. A challenge for the future will be delineation of the physiological significance of the heterogeneous expression of these isoforms in developmental, tissue-specific, and species-specific patterns and or the intra- and intercellular heterogeneity of myosin isoform expression in SM cells of a given organ.

scholarly journals Myosinome: A Database of Myosins from Select Eukaryotic Genomes to Facilitate Analysis of Sequence-Structure-Function Relationships

2012 ◽  
Vol 6 ◽  
pp. BBI.S9902 ◽  
Author(s):  
Divya P. Syamaladevi ◽  
Margaret S Sunitha ◽  
S. Kalaimathy ◽  
Chandrashekar C. Reddy ◽  
Mohammed Iftekhar ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Atp Hydrolysis ◽  
Homo Sapiens ◽  
Relevant Literature ◽  
Myosin Ii ◽  
Coiled Coil ◽  
Structural Features ◽  
Model Organisms ◽  
Congenital Diseases ◽  
C Elegans

Myosins are one of the largest protein superfamilies with 24 classes. They have conserved structural features and catalytic domains yet show huge variation at different domains resulting in a variety of functions. Myosins are molecules driving various kinds of cellular processes and motility until the level of organisms. These are ATPases that utilize the chemical energy released by ATP hydrolysis to bring about conformational changes leading to a motor function. Myosins are important as they are involved in almost all cellular activities ranging from cell division to transcriptional regulation. They are crucial due to their involvement in many congenital diseases symptomatized by muscular malfunctions, cardiac diseases, deafness, neural and immunological dysfunction, and so on, many of which lead to death at an early age. We present Myosinome, a database of selected myosin classes (myosin II, V, and VI) from five model organisms. This knowledge base provides the sequences, phylogenetic clustering, domain architectures of myosins and molecular models, structural analyses, and relevant literature of their coiled-coil domains. In the current version of Myosinome, information about 71 myosin sequences belonging to three myosin classes (myosin II, V, and VI) in five model organisms ( Homo Sapiens, Mus musculus, D. melanogaster, C. elegans and S. cereviseae) identified using bioinformatics surveys are presented, and several of them are yet to be functionally characterized. As these proteins are involved in congenital diseases, such a database would be useful in short-listing candidates for gene therapy and drug development. The database can be accessed from http://caps.ncbs.res.in/myosinome .

scholarly journals Inhibition of acanthamoeba actomyosin-II ATPase activity and mechanochemical function by specific monoclonal antibodies.

1984 ◽  
Vol 99 (3) ◽  
pp. 1024-1033 ◽  
Author(s):  
D P Kiehart ◽  
T D Pollard
Keyword(s):  
Monoclonal Antibodies ◽  
Atpase Activity ◽  
Conformational Changes ◽  
Binding Sites ◽  
Polyclonal Antibodies ◽  
Myosin Ii ◽  
Antigenic Site ◽  
Actin Binding ◽  
Filamentous Form ◽  
Antibody Effects

Monoclonal and polyclonal antibodies that bind to myosin-II were tested for their ability to inhibit myosin ATPase activity, actomyosin ATPase activity, and contraction of cytoplasmic extracts. Numerous antibodies specifically inhibit the actin activated Mg++-ATPase activity of myosin-II in a dose-dependent fashion, but none blocked the ATPase activity of myosin alone. Control antibodies that do not bind to myosin-II and several specific antibodies that do bind have no effect on the actomyosin-II ATPase activity. In most cases, the saturation of a single antigenic site on the myosin-II heavy chain is sufficient for maximal inhibition of function. Numerous monoclonal antibodies also block the contraction of gelled extracts of Acanthamoeba cytoplasm. No polyclonal antibodies tested inhibited ATPase activity or gel contraction. As expected, most antibodies that block actin-activated ATPase activity also block gel contraction. Exceptions were three antibodies M2.2, -15, and -17, that appear to uncouple the ATPase activity from gel contraction: they block gel contraction without influencing ATPase activity. The mechanisms of inhibition of myosin function depends on the location of the antibody-binding sites. Those inhibitory antibodies that bind to the myosin-II heads presumably block actin binding or essential conformational changes in the myosin heads. A subset of the antibodies that bind to the proximal end of the myosin-II tail inhibit actomyosin-II ATPase activity and gel contraction. Although this part of the molecule is presumably some distance from the ATP and actin-binding sites, these antibody effects suggest that structural domains in this region are directly involved with or coupled to catalysis and energy transduction. A subset of the antibodies that bind to the tip of the myosin-II tail appear to inhibit ATPase activity and contraction through their inhibition of filament formation. They provide strong evidence for a substantial enhancement of the ATPase activity of myosin molecules in filamentous form and suggest that the myosin filaments may be required for cell motility.

scholarly journals The central role of the tail in switching off 10S myosin II activity

2019 ◽  
Vol 151 (9) ◽  
pp. 1081-1093 ◽  
Author(s):  
Shixin Yang ◽  
Kyoung Hwan Lee ◽  
John L. Woodhead ◽  
Osamu Sato ◽  
Mitsuo Ikebe ◽  
...  
Keyword(s):  
Atp Hydrolysis ◽  
Myosin Ii ◽  
Active Form ◽  
Sedimentation Coefficient ◽  
Actin Binding ◽  
Myosin Filament ◽  
Particle Analysis ◽  
Compact Structure ◽  
Energy Conserving ◽  
In Cells

Myosin II is a motor protein with two heads and an extended tail that plays an essential role in cell motility. Its active form is a polymer (myosin filament) that pulls on actin to generate motion. Its inactive form is a monomer with a compact structure (10S sedimentation coefficient), in which the tail is folded and the two heads interact with each other, inhibiting activity. This conformation is thought to function in cells as an energy-conserving form of the molecule suitable for storage as well as transport to sites of filament assembly. The mechanism of inhibition of the compact molecule is not fully understood. We have performed a 3-D reconstruction of negatively stained 10S myosin from smooth muscle in the inhibited state using single-particle analysis. The reconstruction reveals multiple interactions between the tail and the two heads that appear to trap ATP hydrolysis products, block actin binding, hinder head phosphorylation, and prevent filament formation. Blocking these essential features of myosin function could explain the high degree of inhibition of the folded form of myosin thought to underlie its energy-conserving function in cells. The reconstruction also suggests a mechanism for unfolding when myosin is activated by phosphorylation.

scholarly journals An insightful myosin structure reveals how actin triggers force production

2014 ◽  
Vol 70 (a1) ◽  
pp. C1056-C1056
Author(s):  
Paola Llinas ◽  
Tatiana Isabet ◽  
Lin Song ◽  
Allan Zhong ◽  
Serena Sirigu ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Molecular Motors ◽  
Structural State ◽  
Atp Hydrolysis ◽  
Mechanical Energy ◽  
Genetic Disorders ◽  
Force Production ◽  
Actin Binding ◽  
Mechanical Coupling ◽  
Hydrolysis Products

Directed force production is essential for life. Allostery is at the heart of the mechanism that cellular nanomotors use to walk, pull or anchor. Such molecular motors are essential for a cell to migrate, to divide and organise the intra-cellular traffic between its compartments. The actin-based motors, myosins, are critical for many of these movements, for muscle contraction, cytokinesis and sophisticated cellular functions such as hearing. Deficit in these motors can lead to a number of human genetic disorders. Force is produced by these motors by the conversion of chemical energy derived from ATP hydrolysis into mechanical energy via the interaction with their track, the actin filament. Biophysical approaches have provided insights into the chemo-mechanical coupling in the actomyosin system. They show how three allosteric sites communicate via relatively small conformational changes in the motor domain that are coupled and amplified by a lever-arm mechanism that produce a working stroke of several nanometers. While ATP binding and hydrolysis are essential for detachment of the motor from its track and its trapping in the pre-stroke conformation, step-wise rebinding to the track triggers controlled release of hydrolysis products upon the working stroke. A reverse motor, myosin VI has been particularly intriguing and informative regarding the force production mechanism. An unpublished structural state not only reveal how trapping of the hydrolysis products stabilize the primed pre-stroke conformation, it also provides insights for the rearrangements triggered by actin to promote Pi release. This new structural state has all the expected features of the Pi release state populated upon motor re-binding to its track. This allows visualization for the first time of the structural rearrangements triggered by actin binding that are coupled to force generation and product release at the beginning of the powerstroke.

scholarly journals Head–Head and Head–Tail Interaction: A General Mechanism for Switching Off Myosin II Activity in Cells

2008 ◽  
Vol 19 (8) ◽  
pp. 3234-3242 ◽  
Author(s):  
Hyun Suk Jung ◽  
Satoshi Komatsu ◽  
Mitsuo Ikebe ◽  
Roger Craig
Keyword(s):  
Smooth Muscle ◽  
Intramolecular Interaction ◽  
Muscle Relaxation ◽  
Myosin Ii ◽  
Actin Binding ◽  
General Mechanism ◽  
Striated Muscles ◽  
Electron Microscopic ◽  
Nonmuscle Cells ◽  
Motile Activity

Intramolecular interaction between myosin heads, blocking key sites involved in actin-binding and ATPase activity, appears to be a critical mechanism for switching off vertebrate smooth-muscle myosin molecules, leading to relaxation. We have tested the hypothesis that this interaction is a general mechanism for switching off myosin II–based motile activity in both muscle and nonmuscle cells. Electron microscopic images of negatively stained myosin II molecules were analyzed by single particle image processing. Molecules from invertebrate striated muscles with phosphorylation-dependent regulation showed head–head interactions in the off-state similar to those in vertebrate smooth muscle. A similar structure was observed in nonmuscle myosin II (also phosphorylation-regulated). Surprisingly, myosins from vertebrate skeletal and cardiac muscle, which are not intrinsically regulated, undergo similar head–head interactions in relaxing conditions. In all of these myosins, we also observe conserved interactions between the ‘blocked’ myosin head and the myosin tail, which may contribute to the switched-off state. These results suggest that intramolecular head–head and head-tail interactions are a general mechanism both for inducing muscle relaxation and for switching off myosin II–based motile activity in nonmuscle cells. These interactions are broken when myosin is activated.

scholarly journals Actin-facilitated assembly of smooth muscle myosin induces formation of actomyosin fibrils

1992 ◽  
Vol 117 (6) ◽  
pp. 1223-1230 ◽  
Author(s):  
D Applegate ◽  
JD Pardee
Keyword(s):  
Smooth Muscle ◽  
Actin Filament ◽  
Active Sites ◽  
Atp Hydrolysis ◽  
Thick Filament ◽  
Smooth Muscle Myosin ◽  
Fiber Assembly ◽  
Thick Filaments ◽  
Filament Networks ◽  
Muscle Myosin

To identify regulatory mechanisms potentially involved in formation of actomyosin structures in smooth muscle cells, the influence of F-actin on smooth muscle myosin assembly was examined. In physiologically relevant buffers, AMPPNP binding to myosin caused transition to the soluble 10S myosin conformation due to trapping of nucleotide at the active sites. The resulting 10S myosin-AMPPNP complex was highly stable and thick filament assembly was suppressed. However, upon addition to F-actin, myosin readily assembled to form thick filaments. Furthermore, myosin assembly caused rearrangement of actin filament networks into actomyosin fibers composed of coaligned F-actin and myosin thick filaments. Severin-induced fragmentation of actin in actomyosin fibers resulted in immediate disassembly of myosin thick filaments, demonstrating that actin filaments were indispensable for mediating myosin assembly in the presence of AMPPNP. Actomyosin fibers also formed after addition of F-actin to nonphosphorylated 10S myosin monomers containing the products of ATP hydrolysis trapped at the active site. The resulting fibers were rapidly disassembled after addition of millimolar MgATP and consequent transition of myosin to the soluble 10S state. However, reassembly of myosin filaments in the presence of MgATP and F-actin could be induced by phosphorylation of myosin P-light chains, causing regeneration of actomyosin fiber bundles. The results indicate that actomyosin fibers can be spontaneously formed by F-actin-mediated assembly of smooth muscle myosin. Moreover, induction of actomyosin fibers by myosin light chain phosphorylation in the presence of actin filament networks provides a plausible hypothesis for contractile fiber assembly in situ.

scholarly journals The Central Role of the Tail in Switching Off Myosin II in Cells

2019 ◽  
Author(s):  
Shixin Yang ◽  
Kyoung Hwan Lee ◽  
John L. Woodhead ◽  
Osamu Sato ◽  
Mitsuo Ikebe ◽  
...  
Keyword(s):  
Atp Hydrolysis ◽  
Myosin Ii ◽  
Actin Binding ◽  
Compact Structure ◽  
Mechanism Of Inhibition ◽  
Energy Conserving ◽  
High Degree ◽  
First Time ◽  
In Cells

AbstractMyosin II is a motor protein playing an essential role in cell motility. The molecule can exist as a polymer that pulls on actin to generate motion, or as an inactive monomer with a compact structure, in which its tail is folded and its two heads interact with each other. This conformation functions in cells as an energy-conserving storage and transport molecule. The mechanism of inhibition is not fully understood. We have carried out a 3D reconstruction of the switched-off form revealing for the first time multiple interactions between the tail and the two heads that trap ATP hydrolysis products, block actin binding, obstruct head phosphorylation, and prevent filament formation. Blocking these essential features of myosin function can explain the high degree of inhibition of the folded form of myosin, serving its energy-conserving, storage function in cells. The structure also suggests a mechanism for unfolding when activated by phosphorylation.

Distribution of c-protein isoforms in sarcomeres of developing chick skeletal muscle

1988 ◽  
Vol 46 ◽  
pp. 226-227
Author(s):  
D. A. Fischman ◽  
J. E. Dennis ◽  
T. Obinata ◽  
H. Takano-Ohmuro
Keyword(s):  
Skeletal Muscles ◽  
Thick Filament ◽  
Protein Isoforms ◽  
Actin Binding ◽  
Striated Muscles ◽  
C Protein ◽  
Sarcomeric Protein ◽  
Thick Filaments ◽  
Cross Bridges ◽  
Bridge Bearing

C-protein is a 150 kDa protein found within the A bands of all vertebrate cross-striated muscles. By immunoelectron microscopy, it has been demonstrated that C-protein is distributed along a series of 7-9 transverse stripes in the medial, cross-bridge bearing zone of each A band. This zone is now termed the C-zone of the sarcomere. Interest in this protein has been sparked by its striking distribution in the sarcomere: the transverse repeat between C-protein stripes is 43 nm, almost exactly 3 times the 14.3 nm axial repeat of myosin cross-bridges along the thick filaments. The precise packing of C-protein in the thick filament is still unknown. It is the only sarcomeric protein which binds to both myosin and actin, and the actin-binding is Ca-sensitive. In cardiac and slow, but not fast, skeletal muscles C-protein is phosphorylated. Amino acid composition suggests a protein of little or no αhelical content. Variant forms (isoforms) of C-protein have been identified in cardiac, slow and embryonic muscles.

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