Sandbox Reserved 930: Difference between revisions
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==Introduction== | ==Introduction== | ||
[[Image:Actin myosin anim.gif|300px|left|thumb| The movement of myosin motor domain on actin filament]] | [[Image:Actin myosin anim.gif|300px|left|thumb| Figure 1. The movement of myosin motor domain on actin filament]] | ||
[[Image:myosin.png|300px|right|thumb| The contractile cycle of the myosin head]] | [[Image:myosin.png|300px|right|thumb| Figure 2. The contractile cycle of the myosin head]] | ||
In the striated muscle the actin and myosin proteins form ordered basic units called sarcomeres. Muscle contraction is achieved by the mechanical sliding of myosin filament (thick filament) along the actin filament (thin filament), Fig. 1. The major constituent of the myosin filament is myosin, a motor protein responsible for converting chemical energy to mechanical movement. In the presence of Ca<sup>2+</sup> and Mg<sup>2+</sup>, myosin is able to cyclically bind ATP and hydrolyse it to ADP + P<sub>i</sub> , triggering subsequent myosin-actin detachment, reattachment and power stroke, so called contractile reaction (Fig.2). | In the striated muscle the actin and myosin proteins form ordered basic units called sarcomeres. Muscle contraction is achieved by the mechanical sliding of myosin filament (thick filament) along the actin filament (thin filament), Fig. 1. The major constituent of the myosin filament is myosin, a motor protein responsible for converting chemical energy to mechanical movement. In the presence of Ca<sup>2+</sup> and Mg<sup>2+</sup>, myosin is able to cyclically bind ATP and hydrolyse it to ADP + P<sub>i</sub> , triggering subsequent myosin-actin detachment, reattachment and power stroke, so called contractile reaction (Fig.2). | ||
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==The subdomains of the motor domain== | ==The subdomains of the motor domain== | ||
[[Image:SUBDOMAINS.gif|300px|right|thumb| The contractile cycle of the myosin head]] | [[Image:SUBDOMAINS.gif|300px|right|thumb|Figure 3. The contractile cycle of the myosin head]] | ||
The MD of S1 unit is most frequently described as consisting of 4 subdomains: the converter, the N-terminal subdomain, and upper and lower 50-kDa subdomains <ref>PMID: 10338210</ref>. They are linked together by 3 single-stranded joints termed the switch II (residue IIe-461 to Asn-470), the relay (residues Asn-489 to ASP-519), and SH1 helix (Cys-693 to Phe-707)(Fig. 3) <ref>PMID: 11016966</ref>. | The MD of S1 unit is most frequently described as consisting of 4 subdomains: the converter, the N-terminal subdomain, and upper and lower 50-kDa subdomains <ref>PMID: 10338210</ref>. They are linked together by 3 single-stranded joints termed the switch II (residue IIe-461 to Asn-470), the relay (residues Asn-489 to ASP-519), and SH1 helix (Cys-693 to Phe-707)(Fig. 3) <ref>PMID: 11016966</ref>. | ||
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==Conclusions== | ==Conclusions== | ||
The conformational changes of the myosin head during the contractile cycle allow the myosin filaments to slide across the actin filaments in the muscle sarcomere, producing movement. Scallop myosin is an exceptional system in that it is the first myosin isoform that has crystallized in all the three states of the contraction cycle: the rigor state, transition state and the detached state. However, not all conformational changes and interactions of the S1 with the nucleotides are known, even though kinetic studies and electron microscopy (EM) have helped to understand the mechanism of the contractile cycle along with the information from structural studies. Future perspectives for muscle and myosin research are to characterize a structure with S1 bound to actin, elucidate the structural details of how nucleotide binding is coupled to actin affinity, and to define the various conformational states of myosin in species other than scallop. | The conformational changes of the myosin head during the contractile cycle allow the myosin filaments to slide across the actin filaments in the muscle sarcomere, producing movement. Scallop myosin is an exceptional system in that it is the first myosin isoform that has crystallized in all the three states of the contraction cycle: the rigor state, transition state and the detached state. However, not all conformational changes and interactions of the S1 with the nucleotides are known, even though kinetic studies and electron microscopy (EM) have helped to understand the mechanism of the contractile cycle along with the information from structural studies. Future perspectives for muscle and myosin research are to characterize a structure with S1 bound to actin, elucidate the structural details of how nucleotide binding is coupled to actin affinity, and to define the various conformational states of myosin in species other than scallop. | ||
