Cytoskeleton. It is the monomer subunit of microfilaments, one of the three major components of the cytoskeleton, and of thin filaments which are part of the contractile apparatus in muscle cells. It is the most abundant protein in the typical eukaryotic cell, accounting for about 15% in some cell types. The protein is highly conserved, and forms a huge variety of structure in cells in concert with of act in binding proteins. The act in filaments interact with myosin to produce a sliding effect, which is the basis of muscular contraction and many aspects of cell motility, including cytokinesis. The individual subunits of act in are known as globular act in (G - act in) that assembles into long filamentous polymers called F - act in. Two parallel F - act in strands twist around each other in a helical formation, giving rise to microfilaments of the cytoskeleton. Microfilaments measure approximately 7 nm in diameter, with a loop of the helix repeating every 37 nm. Each act in promoter binds one molecule of ATP and has one high affinity site for either calcium or magnesium ions, as well as several low affinity sites. It exists as a monomer in low salt concentrations, but filaments form rapidly as salt concentration rises, with the consequent hydrolysis of ATP. Act in from many sources forms a tight complex with deoxyribonucleic (DNAs) although the significance of this is still unknown. The formation of this complex results in the inhibition of DNAs I activity, and act in loses its ability to polymerize. It has been shown that an ATP domain of act in shares similarity with ATP domains in hsp70 proteins. In vertebrates there are three groups of act in isoforms: alpha, beta and gamma. The alpha act ins are found in muscle tissues and are a major constituent of the contractile apparatus. The beta and gamma act ins co-exist in most cell types as components of the cytoskeleton and as mediators of internal cell motility. MRE B, a major component of the bacterial cytoskeleton, exhibits high structural homology to its eukaryotic counterpart, act in. Further it has been suggested that members of the Rho family of small guano sine triphosphates have emerged as key regulators of the act in cytoskeleton, and through their interaction with multiple target proteins, they ensure coordinated control of other cellular activities such as gene transcription and adhesion.
Muscle:
Muscle is contractile tissue grouped into coordinated systems for greater efficiency. In humans, the muscle systems are classified by gross appearance and location of cells. The three types of muscles are striated (or skeletal), cardiac, and smooth (or nonstriated). Striated muscle is almost exclusively attached to the skeleton and constitutes the bulk of the body’s muscle tissue. The multinucleated fibers are under the control of the somatic nervous system and elicit movement by forces exerted on the skeleton similar to levers and pulleys. The rhythmic contraction of cardiac muscle is regulated by the sinoatrial node, the heart’s pacemaker. Although cardiac muscle is specialized striated muscle consisting of elongated cells with many centrally located nuclei, it is not under voluntary control. Smooth muscle lines the viscera, blood vessels, and dermis, and, like cardiac muscle, its movements are operated by the autonomic nervous system and thus are not under voluntary control. The nucleus of each short tapering cell is located centrally.
Reference :
Act in isoforms. Curs, Opine, Cell Biol. 1993 Feb;5(1):48-55, Herman 'IM'.
The assembly of MRE B, a prokaryotic homolog of act in. The assembly of MRE B, a prokaryotic homolog of act in. 2005 Jan 28;280(4):2628-35. EPUB 2004 Nov 16.
Rho GTP and the Act in Cytoskeleton Science, 23 January 1998.
You must be logged in to post a comment.