Muscle contraction conformation change

FIGURE 5-33 Molecular mechanism of muscle contraction. Conformational changes in the myosin head that are coupled to stages in the ATP hydrolytic cycle cause myosin to successively dissociate from one actin subunit, then associate with another farther along the actin filament. In this way the myosin heads slide along the thin filaments, drawing the thick filament array into the thin filament array (see Fig. 5-32). 

Calcium is the trigger behind the muscle contraction process (24,25). Neural stimulation activates the release of stored Ca(Il) resulting in a dramatic increase in free calcium ion levels. The subsequent binding of Ca(Il) resulting in a dramatic increase in free calcium ion levels. The subsequent binding of Ca(Il) to the muscle protein troponin C provides the impetus for a conformational change in the troponin complex and sets off successive events resulting in muscle contraction. 

Figure 14.12 The swinging cross-bridge model of muscle contraction driven by ATP hydrolysis, (a) A myosin cross-bridge (green) binds tightly in a 45 conformation to actin (red), (b) The myosin cross-bridge is released from the actin and undergoes a conformational change to a 90 conformation (c), which then rebinds to actin (d). The myosin cross-bridge then reverts back to its 45° conformation (a), causing the actin and myosin filaments to slide past each other. This whole cycle is then repeated.

FIGURE 17.23 The mechanism of skeletal muscle contraction. The free energy of ATP hydrolysis drives a conformational change in the myosin head, resulting in net movement of the myosin heads along the actin filament. Inset) A ribbon and space-filling representation of the actin—myosin interaction. (SI myosin image courtesy of Ivan Rayment and Hazel M. Holden, University of Wiseonsin, Madison.)... 

CHANGES IN THE CONFORMATION OF THE HEAD OF MYOSIN DRIVE MUSCLE CONTRACTION... 

How can hydrolysis of ATP produce macroscopic movement Muscle contraction essentially consists of the cychc attachment and detachment of the S-1 head of myosin to the F-actin filaments. This process can also be referred to as the making and breaking of cross-bridges. The attachment of actin to myosin is followed by conformational changes which are of particular importance in the S-1 head and are dependent upon which nucleotide is present (ADP or ATP). These changes result... 

When your muscles contract it is largely because many C-C sigma (single) bonds are undergoing rotation (conformational changes) in a muscle protein called... 

Calcium couples muscle membrane excitation to filament contraction. Important work has focused on the proteins present in the T-tubule/SR junction. One protein, an integral component of the T-tubular membrane, is a form of L-type, dihydropyridine-sensitive, voltage-dependent calcium channel. Another, the ryanodine receptor (RyR), is a large protein associated with the SR membrane in the triad that may couple the conformational changes in the Ca2+ channel protein induced by T-tubular depolarization to the Ca2+ release from the SR (Fig. 43-6). 

Troponin C in muscle is structurally closely related to catmodulin. It has 4 EF structures, of which only two can be occupied by Ca. Troponin C is a component of the contraction apparatus of muscle. Ca binding to troponin C induces a conformational change in the troponin complex that leads to contraction of muscle. 

Direct hydrolysis of ATP is the source of energy in the conformational changes that produce muscle contraction but, in general, it is not ATP hydrolysis but the transfer of a phosphoryl, pyrophosphoryl, or adenylyl group from ATP to a substrate or enzyme molecule that couples the energy of ATP breakdown to endergonic transformations of substrates. 

Regulatory processes such as muscle contraction are controlled by temporary conformational changes associated with metal ion co-ordination. Such regulatory processes are frequently associated with metal ions such as Mg2+, Ca2+ and Mn2+ (which possesses a d5 configuration with no crystal field preference for any particular co-ordination geometry). Muscle contraction is controlled by the binding of calcium ions to the protein troponin (Fig. 10-4), with a feed-back loop controlling the release and uptake of calcium ions from an ATP-ase, an enzyme which catalyses the hydrolysis of ATR... 

Troponin s role in the thin filament of vertebrate striated muscles is primarily that of regulation. The three subunits of this complex form what has been described as a Ca2+-sensitive latch that fixes tropomyosin s position on the actin helix in the off state of contraction (Lehman et al., 2001). One subunit of the complex, troponin T (TnT), maintains an invariant linkage to tropomyosin, and another, troponin I (Tnl), a variable linkage to actin. The third subunit, troponin (TnC) is the Ca2+sensor of the complex and indeed of the myofibril itself. The latch is opened or closed depending on the level of Ca2+. Correspondingly, a series of conformational changes takes place in the entire complex and in the thin... 

The cyclic formation and dissociation of complexes between the actin filaments and the SI heads of myosin leads to contraction of the muscle. On binding to actin, myosin releases its bound Pj and ADP. This causes a conformational change to occur in the protein which moves the actin filament along the thick filament. ATP then binds to myosin, displacing the actin. Hydrolysis of the ATP returns the SI head to its original conformation. 

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