Muscle
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella in Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
The predominant protein, actin, consists of spherical subunits (globular actin) arranged into two chains twisted around each other (fibrous actin). (Imagine two strands of pearls twisted around each other.) Tropomyosin is a long, thread-like protein found on the outer surface of the actin chain. Each tropomyosin molecule is associated with 6–7 actin subunits. The function of tropomyosin is to cover the binding sites for myosin on the actin subunits when the muscle is in the resting state. This prevents the interaction between actin and myosin that causes muscle contraction. Troponin is a smaller protein consisting of three subunits. One subunit binds to actin, another binds to tropomyosin and the third binds with calcium. When the muscle is relaxed, troponin holds the tropomyosin in its blocking position on the surface of the actin (see Figure 16.1, panel b).
Muscle Physiology and Electromyography
Verna Wright, Eric L. Radin in Mechanics of Human Joints, 2020
Actin is composed of strings of globular protein, about 5.5 nm in diameter, called G-actin. The strings are wound around each other in a helical arrangement, and another protein, tropomyosin B, lies in the groove between them. A third protein, troponin, is bound onto the tropomyosin B at intervals of 40 nm (see Fig. 5). The myosin filaments are 12 nm in diameter and have lateral projections which point toward the actin filaments (7,8). Each myosin molecule has two distinct subunits, light meromyosin (most of the tail) and heavy mero-myosin (the head and proximal part of the tail; see Fig 6). Myosin filaments are held together by twining of the individual tails; the heads project in a regular pattern, usually in groups of three (although this can sometimes be two or four) every 14.3 run. Each of these heads is set at 120° to its neighbors, so that a spiral pattern is formed along the length of the filament.
The cardiac myocyte: excitation and contraction
Neil Herring, David J. Paterson in Levick's Introduction to Cardiovascular Physiology, 2018
The thin actin filament is 1.05 μm long × 6 nm wide. Actin filaments are interposed between the myosin fila-ments, with one end free in the A band and the other rooted in the Z line. The actin filaments form the pale I (isotropic) band. The I band is only ~0.25 μm wide, because most of the actin filament is in the space between the myosin filaments, in the A band. In other words, the actin and myosin fila-ments interdigitate. The filamentous actin (F-actin) is a poly-mer of globular actin subunits (G‑actin), which are bonded side-by-side. The thin filament consists of two such F-actin strings, arranged as a two-stranded helix (Figure 3.3). The groove of the double helix contains a regulatory protein, tropomyosin. Also, a regulatory complex composed of tro-ponins is attached to the tropomyosin and actin at regular intervals. The tropomyosin–troponin complex plays a key role in initiating contraction.
Novel ligands and modulators of triggering receptor expressed on myeloid cells receptor family: 2015-2020 updates
Published in Expert Opinion on Therapeutic Patents, 2021
Harbinder Singh, Vikrant Rai, Sunil K. Nooti, Devendra K. Agrawal
Actin is a family of multi-functional globular proteins present in all eukaryotic cells which has been found to participate in various cellular processes, including muscle contraction, cell division and cytokinesis, cell motility, cell signaling, etc. It was observed that actin could activate the inflammatory response by interacting through TREM-1 [56]. There was a controversy on the presence of actin on the cell surface since actin is a cellular cytoskeleton protein. Besides its presence in the cytoplasm, its distribution was also detected on the surface of platelets in the resting state [57]. Therefore, platelets provide surface actin for TREM-1 recognition to activate signaling. In 2017, Fu et al. found that recombinant actin can directly interact with the recombinant TREM-1 extracellular domain and enhance inflammatory response when injected in wild-type mice but not in TREM-1−/- mice. This amplification of inflammatory response could be inhibited by peptide LP17. It was confirmed that the extracellular actin is co-localized with TREM-1 in the lung tissues of septic mice [56].
Does familial Mediterranean fever affect cognitive function in children? Electrophysiological preliminary study
Published in International Journal of Neuroscience, 2018
Gonca Keskindemirci, Gökçer Eskikurt, Nuray Aktay Ayaz, Mustafa Çakan, Numan Ermutlu, Ümmühan İşoğlu Alkaç
It is thought that the main mechanism of colchicine in treating FMF is depolymerization of microtubules through the formation of a tubulin–colchicine complex. Colchicine also causes globular actin to transform into filamentous actin through polymerization [23–25]. Actin usually exists as globular actin (G-actin) and filament/filamentous actin (F-actin) in the body. F-actin is the active form of the molecule and has an important function at the synapses. The active zone of the synapse has an important role in moving vesicles into the synapse and at the presynaptic bouton, and F-actin acts as scaffolding. Recently, actin was found to have a role in the formation of axonal branches that result in new boutons. It is also associated with the formation of new synapses and causes changes that promote long-term potentiation, which relates to learning and memory. All these effects could have roles in cell communication, learning, and memory, and might positively contribute to some cognitive functions. Increased P300 amplitude, which reflects working memory capacity, and improved allocation of attention can be attributed to the effect of colchicine on actin polymerization [26,27].
Regulation of differentiation of MEG01 to megakaryocytes and platelet-like particles by Valproic acid through Notch3 mediated actin polymerization
Published in Platelets, 2019
Ankita Dhenge, Rutuja Kuhikar, Vaijayanti Kale, Lalita Limaye
Levels of polymerized (F-actin) and depolymerized (G-actin) forms of actin were measured. Equal numbers (0.5X106) of untreated and VPA-treated cells were lysed in actin stabilizing buffer (0.1 M PIPES [piperazine-N,N0-bis{2-ethane-sulfonic acid}], 30% glycerol, 5% DMSO, 1mM MgSO4,1mM EGTA, 1% Triton X-100,1mM ATP and 40 mg/mL protease inhibitor cocktail). The cells were dislodged by scraping, and entire extract was centrifuged at 4°C for 75 min at 16000g. The supernatant containing G-actin was separated, and the pellet containing F-actin was solubilized with actin depolymerization buffer (0.1 M PIPES pH = 6.9, 1mM MgSO4, 10mM CaCl2, 5μM Cytochalasin D). The supernatant and the pellets were resuspended separately in protein lysis buffer and analyzed by western blotting with β-actin antibody.
Related Knowledge Centers
- Cytoskeleton
- Eukaryote
- Globular Protein
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- Monomer
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- Myofibril
- Protein
- Protein Subunit
- Protein Family