Titin filament system

The thick filament system, which comprises myosin protein, connected from the M-line to the Z-disc by titin (connectin), and myosin-binding protein C, which binds at one end to the thick filament and at the other to actin. 

The M-band proteins myomesin, as well as M-protein, cross-link the thick-filament system (myosins) and the M-band part of titin (the elastic filaments). 

The present volume covers Muscle and Molecular Motors . The first few chapters describe the ultrastructures of striated muscles and of various muscle filaments (myosin, actin, titin), they discuss the regulation of muscle contractile activity, and they explore the mechanism of force production and movement. The book then sets out to survey other kinds of motor systems microtubules and their interactions with both microtubule associated proteins (MAPs) and the motor proteins kinesin and dynein, the major sperm protein in nematodes, the rotary ATPases driven by or driving proton gradients, and the action of motor enzymes, polymerases, on nucleic acids. The aim throughout is to explore different molecular mechanisms of motor action in order to identify common themes. 

There are two additional proteins. Firstly sometimes a meshwork of scaffolding proteins can be recognized between the middle parts of the myosin filaments, probably stiffening them in their center regions. Electron microscopically they form the M-line (Fig. 9.2). Secondly a protein called titin is located between the ends of the Myosin filaments and the Z-membranes. This can only be seen by the electron microscope after special preparations. Due to its elasticity the system of myofibrils and therewith the total muscle becomes extensible. This is important for the muscles ability to store energy when passively stretched. 

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