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 LOCALIZATION OF MYOSIN FILAMENTS IN SMOOTH MUSCLE

1968 ◽  
Vol 37 (1) ◽  
pp. 105-116 ◽  
Author(s):  
Robert E. Kelly ◽  
Robert V. Rice
Keyword(s):  
Smooth Muscle ◽  
Cross Section ◽  
Striated Muscle ◽  
Thick Filament ◽  
Longitudinal Axis ◽  
Thin Filaments ◽  
Chicken Gizzard ◽  
Thick Filaments ◽  
Myosin Filaments ◽  
Muscle Myosin

Thick myosin filaments, in addition to actin filaments, were found in sections of glycerinated chicken gizzard smooth muscle when fixed at a pH below 6.6. The thick filaments were often grouped into bundles and run in the longitudinal axis of the smooth muscle cell. Each thick filament was surrounded by a number of thin filaments, giving the filament arrangement a rosette appearance in cross-section. The exact ratio of thick filaments to thin filaments could not be determined since most arrays were not so regular as those commonly found in striated muscle. Some rosettes had seven or eight thin filaments surrounding a single thick filament. Homogenates of smooth muscle of chicken gizzard also showed both thick and thin filaments when the isolation was carried out at a pH below 6.6, but only thin filaments were found at pH 7.4. No Z or M lines were observed in chicken gizzard muscle containing both thick and thin filaments. The lack of these organizing structures may allow smooth muscle myosin to disaggregate readily at pH 7.4.

scholarly journals The carboxyl-terminal isoforms of smooth muscle myosin heavy chain determine thick filament assembly properties

2002 ◽  
Vol 156 (1) ◽  
pp. 113-124 ◽  
Author(s):  
Arthur S. Rovner ◽  
Patricia M. Fagnant ◽  
Susan Lowey ◽  
Kathleen M. Trybus
Keyword(s):  
Smooth Muscle ◽  
Thick Filament ◽  
Smooth Muscle Myosin ◽  
Myosin Isoforms ◽  
Heavy Chains ◽  
Filament Assembly ◽  
Filament Structure ◽  
Alternatively Spliced ◽  
Muscle Myosin

The alternatively spliced SM1 and SM2 smooth muscle myosin heavy chains differ at their respective carboxyl termini by 43 versus 9 unique amino acids. To determine whether these tailpieces affect filament assembly, SM1 and SM2 myosins, the rod region of these myosin isoforms, and a rod with no tailpiece (tailless), were expressed in Sf 9 cells. Paracrystals formed from SM1 and SM2 rod fragments showed different modes of molecular packing, indicating that the tailpieces can influence filament structure. The SM2 rod was less able to assemble into stable filaments than either SM1 or the tailless rods. Expressed full-length SM1 and SM2 myosins showed solubility differences comparable to the rods, establishing the validity of the latter as a model for filament assembly. Formation of homodimers of SM1 and SM2 rods was favored over the heterodimer in cells coinfected with both viruses, compared with mixtures of the two heavy chains renatured in vitro. These results demonstrate for the first time that the smooth muscle myosin tailpieces differentially affect filament assembly, and suggest that homogeneous thick filaments containing SM1 or SM2 myosin could serve distinct functions within smooth muscle cells.

scholarly journals The Small Molecule Smooth Muscle Myosin Inhibitor, CK-2018571, Selectively Inhibits ATP Hydrolysis and Relaxes Smooth Muscle In Vitro

2010 ◽  
Vol 98 (3) ◽  
pp. 353a ◽  
Author(s):  
Sheila Clancy ◽  
Zhiheng Jia ◽  
Malar Pannirselvam ◽  
Xiangping Qian ◽  
Bradley Morgan ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Small Molecule ◽  
Atp Hydrolysis ◽  
Smooth Muscle Myosin ◽  
Muscle Myosin

scholarly journals MYOSIN-LIKE AGGREGATES IN TRYPSIN-TREATED SMOOTH MUSCLE CELLS

1971 ◽  
Vol 48 (1) ◽  
pp. 174-188 ◽  
Author(s):  
Jack Rosenbluth
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Muscle Protein ◽  
Muscle Cells ◽  
Smooth Muscle Myosin ◽  
Stable Complex ◽  
Solution Ph ◽  
Thin Sections ◽  
Thick Filaments ◽  
Muscle Myosin

Segments of the lower small intestine of the toad Bufo marinus were excised and soaked for approximately 2 hr in Ringer's solution (pH 7.4 or 7.8) containing crystalline trypsin and then fixed for electron microscopy at approximately the same pH. Thin sections of the tunica muscularis of these specimens show smooth muscle cells ranging in appearance from severely damaged at one extreme to apparently unaffected at the other. Among these are cells at intermediate stages, including some which exhibit large and conspicuous populations of thick filaments closely resembling artificially prepared aggregates of smooth muscle myosin. The thick filaments have the form of tactoids ∼ 250–300 A in diameter in their middle regions and are ∼ 0.5–1.0 µ in length. In some preparations they also display an axial periodicity approximating 143 A. They are usually randomly oriented and segregated from the thin filaments, which tend to form closely packed, virtually crystalline bundles at the periphery of these cells. "Dense bodies" are absent from cells showing these changes. The simplest interpretation of these data is that smooth muscle myosin normally exists among the actin filaments in a relatively disaggregated state and that trypsin induces aggregation by altering the conformation of the myosin molecule. Alternatively, trypsin may act indirectly through an effect on some other smooth muscle protein which normally forms a stable complex with relatively disaggregated myosin.

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