Myosin head domain

Reconditi, M., Koubassova, N., Linari, M., Dobbie, I., Narayan, T. Diat,0., Piazzesi, G., Lombardi, V., and Irving, M. (2003). The conformation of myosin head domains in rigor muscle determined by X-ray interference. Biophys.J. 85, 1098-1110. 

Figure 34.19. Thick Filament. (A) An electron micrograph of a reconstituted thick filament reveals the presence of myosin head domains at each end and a relatively narrow central region. (B) A schematic view shows how myosin molecules come together to form the thick filament. [Part A courtesy of Dr. Hugh Huxley.]...

All myosins consist of one or two heavy chains and several light chains, which generally have a regulatory function. A characteristic head, neck, and tail domain organization Is found In all myosin heavy chains. Myosin II and myosin V are dimers In which ct-helical sequences In the tail of each heavy chain associate to form a rodlike colled-coll structure. In contrast some myosins, including myosin I, are monomers because their heavy chains lack this ct-hellcal sequence. All myosin head domains have ATPase activity and... 

The role of a particular myosin in vivo is related to its tail domain. For example, the tail domains of myosins I, V, VI, and XI bind the plasma membrane or the membranes of intracellular organelles as a result, these molecules have membrane-related activities (Figure 19-16a). In contrast, the coiled-coil tail domains of myosin II dimers associate to form bipolar thick filaments in which the heads are located at both ends of the filament and are separated by a central bare zone devoid of heads (Figure 19-16b). The close packing of myosin molecules into thick filaments, which are a critical part of the contractile apparatus in skeletal muscle, allows many myosin head domains to interact simultaneously with actin filaments. 

Actomyosin structure. The actin thin filament is shown as the gray line on the right. One monomer of myosin is shown in purple, with the thick vertical part representing part of the thick filament. For clarity, the other monomer of the dimer, and additional myosin molecules in the thick filament, are not shown. The myosin head domain is shown interacting with the thin filament. The ATP binding site is shown as an indentation... 

In this chapter we will describe the general features of the molecule that is the molecular motor of vertebrate smooth muscle cells. As shown in Fig. 1, this myosin molecule is composed of two heavy chains of approximately 220 kDa each and two pairs of light chains that are located in the neck region, just carboxyl-terminal to the globular myosin head domain. The properties and structure of the myosin light chains are covered in Chapter 2 of this volume. 

Figure 14.15 Stmcture of the SI fragment of chicken myosin as a Richardson diagram (a) and a space-filling model (b). The two light chains are shown in magenta and yellow. The heavy chain is colored according to three proteolytic fragments produced by trypsin a 25-kDa N-terminal domain (green) a central 50-kDa fragment (red) divided by a cleft into a 50K upper and a 50K lower domain and a 20-kDa C-terminal domain (blue) that links the myosin head to the coiled-coil tail. The 50-kDa and 20-kDa domains both bind actin, while the 25-kDa domain binds ATP. [(b) Courtesy of 1. Rayment.]...

Figure 1. An unrooted phylogenetic tree of the myosins based on the amino acid sequence comparison of their head domains demonstrating the division of the myosin superfamily into nine classes. The lengths of the branches are proportional to the percent of amino acid sequence divergence and a calibration bar for 5% sequence divergence is shovk n. The different classes of myosins have been numbered using Roman numerals in rough order of their discovery and hypothetical models of the different myosin structures are shown. Question marks indicate either hypothetical or unknown structural features, and only a fraction of the known myosins are shown. (Taken, in modified form, from Cheney et al., 1993).

Walsh There s strong evidence that it is anchored to the actin filament through an N-terminal domain that Jim Stull s group has defined very precisely. The age-old question remains how does an anchored MLCK molecule gain access to an adequate number of myosin heads to account for the phosphorylation stoichiometry that can be achieved in muscle ... 

A myosin head is made up of 850 residues, but the motor domain of a kinesin contains only -345. Like... 

Examining these structures and the fact that they are all powered by ATP, the question remains as to how force is actually produced. Geeves and Holmes (2005) argue that myosin acts by the specific coupling between different myosin head states and different positions of the lever arm on the motor domain, so that, once attached to actin, the myosin acts as an ATP-driven motor where the energy released by ATP hydrolysis is direcdy coupled to the performance of mechanical work. However, Marx et al. (2005) argue that in some cases the kinesins appear to act as thermal ratchets. In this case, the attachment of a second head, once the first head has bound, is an event controlled by thermal motion, but, presumably for steric reasons, the head is more likely to bind to the microtubule in the... 

Fig. 15. Stereo views of the different myosin head, SI, structures showing their variable conformations in different crystal structures. (A) The heads with their motor domains superimposed and oriented as if interacting with a vertical actin filaments in the rigor conformation, Z-band bottom and M-band top. (B) The same structures in a view down the actin filament long axis, looking from the M-band towards the Z-band. Blue is the Dominguez et al. (1998) structure of SI in chicken smooth muscle with ADP.AIF4 bound, orange is the insect flight muscle SI in the ADP.Pj state (Al-Khayat et al., 2003), yellow is scallop SI crystal structure in the ADP.VO4 state (Houdusse et al., 1999), and green is the chicken skeletal muscle with no nucleotide bound (Rayment et al., 1993a).

Fig. 16. (A) Myosin head SI showing the two domains referred to as the motor domain...

Fig. 30. Comparison of the X-ray-modeled myosin head arrays in relaxed fish muscle (A) and relaxed insect flight muscle (B), with the motor (catalytic) domain of outer myosin heads in each model circled to show the close similarity of their configurations in the two different species. The M-band is at the bottom in both models.

Cremo, C. R., and Geeves, M. A. (1998). Interaction of actin and ADP with the head domain of smooth muscle myosin Implications for strain-dependent ADP release in smooth muscle. Biochemistry 37, 1969-1978. 

Villin is an example of a bundling protein. Villin is found in the microvilli of, for example, intestinal brush border cells (Fig. 5-30). The microvilli greatly increase the surface area of the cells, which is essential for effective absorption to take place. Each microvillus extends about 2 p.m into the lumen of the gut and is supported by 20 or so actin filaments tightly bundled by villin (and other proteins) at regular intervals. In a feature common to many actin-based networks, all the filaments in the bundle are oriented with their barbed ends in the same direction, in this case toward the tip of the microvillus where they terminate. Cross-linking of the actin filaments to the plasma membrane occurs via a second protein from the myosin-1 family (a relative of the well-known contractile protein myosin-II). This protein binds its head domain to the sides of the filaments and embeds its tail domain into the membrane. 

Brown, L.J., Klonis, N., Sawyer, W. H., Fajer. P.G. and Hambly, B.D (2001) Independent movement of the regulatory and catalytic domains of myosin heads revealed by phosphorescence anisotropy, Biochemistry 40, 8283-8291. 

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