Myosin coiled coil structure

Fibrinogen is a fibrous protein that was first classified with keratin, myosin, and epidermin based on its 5.1 A repeat in wide-angle X-ray diffraction patterns (Bailey et al., 1943), which was later discovered to be associated with the Q-helical coiled-coil structure. It is a glycoprotein normally present in human blood plasma at a concentration of about 2.5 g/L and is essential for hemostasis, wound healing, inflammation, angiogenesis, and other biological functions. It is a soluble macromolecule, but forms a clot or insoluble gel on conversion to fibrin by the action of the... 

Various theories have been introduced to explain the relative movemoit. Huxley proposed that the myosin head changed its orientation after binding to actin (die "rotating-head" model). According to the helix-coil transition, the normally o-helical coiled-coil structure "melts" to a random coil conformation, which implies a reduction in length. Movements of the myosin tails, as well as conformation changes of the actin have also been considered. It now seems clear, however, that the force production takes place in or very near the myosin heads [22]. Furthermore, among the three different states of myosin - empty actin site, ATP bound to the actin site and ADP-Pi boimd to die actin site - aU of which can... 

Sketch the general structure of the polypeptide backbone of a myosin molecule. Describe the subunit composition of myosin, and note its a-helical coiled-coil structure and its dual globular head. 

Tropomyosin 3 (TMP3, also known as TRK or NEMl) gene located on chromosome lq25 encoding a 284 amino acid protein with coiled coil structure involved in the calcium-dependent actin-myosin interaction. This gene is the fusion partner of the ALK gene in the t(l 2)(q25 p23) translocation. This translocation seems to be the most common translocation associated with the inflammatory myofibroblastic tumor but it is also detected in other tumors such as the anaplastic large cell lymphoma discussed in a later section. 

Each thick filament is composed of about 250 myosin molecules. Myosin has two important roles a structural one as the building block for thick filaments and a functional one as the catalyst of the breakdown of adenosine triphosphate (ATP) during contraction and its interaction with actin as part of the muscle force generator. Actin is an important constituent of the thin filament. The molecular mass of myosin is about 500000 it contains two major protein chains and four small ones, the entire molecule being about 160 nm long, and has a coiled-coil structure. The interaction of actin and myosin provides a basis for molecular models of force generation and contraction in living muscle. 

Fibrous proteins can serve as structural materials for the same reason that other polymers do they are long-chain molecules. By cross-linking, interleaving and intertwining the proper combination of individual long-chain molecules, bulk properties are obtained that can serve many different functions. Fibrous proteins are usually divided in three different groups dependent on the secondary structure of the individual molecules coiled-coil a helices present in keratin and myosin, the triple helix in collagen, and P sheets in amyloid fibers and silks. 

Fibrous proteins are long-chain polymers that are used as structural materials. Most contain specific repetitive amino acid sequences and fall into one of three groups coiled-coil a helices as in keratin and myosin triple helices as in collagen and p sheets as in silk and amyloid fibrils. 

Repeating Structural Elements Are the Secret of Myosin s Coiled Coils... 

An individual polypeptide in the a-keratin coiled coil has a relatively simple tertiary structure, dominated by an a-helical secondary structure with its helical axis twisted in a left-handed superhelix. The intertwining of the two a-helical polypeptides is an example of quaternary structure. Coiled coils of this type are common structural elements in filamentous proteins and in the muscle protein myosin (see Fig. 5-29). The quaternary structure of a-keratin can be quite complex. Many coiled coils can be assembled into large supramolecular complexes, such as the arrangement of a-keratin to form the intermediate filament of hair (Fig. 4-1 lb). 

Myosins II from other sources have similar structures. For example, analysis of the DNA sequence for a heavy chain gene from the nematode Caenorhabditis showed that the protein contains 1966 residues, 1095 of which contain an amino acid sequence appropriate for a 160-nm long coiled coil.123 There are no prolines within this sequence, which lies between Pro 850 and... 

The two-stranded a-helical coiled coil is now recognized as one of natures favorite ways of creating a dimerization motif and has been predicted to occur in a diverse group of over 200 proteins.111 This structure consists of two amphipathic, right-handed a-helices that adopt a left-handed supercoil, analogous to a two-stranded rope where the nonpolar face of each a-helix is continually adjacent to that of the other helix. 2 This structure was first postulated by Crick to explain the X-ray diffraction pattern of a-keratin in the absence of sequence information.Pl The coiled-coil dimerization motif is natures way of creating a rod-like molecule that perhaps plays only a structural role in many fibrous proteins, such as the kmef (keratin, myosin, epidermis, fibrinogen) class 3,4 and the intermediate filament proteins)5 6 ... 

A second widely used sequence-based approach relies on matrices of residue frequencies, pioneered by Parry (1982). He showed that the residue distribution at the seven heptad positions of the putative coiled-coil segments of myosin, tropomyosin, o-keratin, and hemaglutinin are asymmetric, and proposed a method by which the residue frequencies could be used to predict whether a sequence of unknown structure would form a coiled coil. This approach was implemented with modifications in... 

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