Sandbox Reserved 930: Difference between revisions

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• Lower and upper 50-kDa subdomains form the interface where actin can bind <ref name="houdusse2000"> PMID: 11016966</ref>
• Lower and upper 50-kDa subdomains form the interface where actin can bind <ref name="houdusse2000"> PMID: 11016966</ref>


Conformational changes in the flexible joints coordinate rearrangements of the four MD subdomains enabling the transition between different myosin S1 conformations in the actomyosin contractile cycle, during which S1 traduces ATP hydrolysis to mechanical work. The different conformational states of myosin are termed strong or weak actin-binding states <ref>PMID: 15184651</ref>.
Conformational changes in the flexible joints coordinate rearrangements of the four MD subdomains enabling the transition between different myosin S1 conformations in the actomyosin contractile cycle, during which S1 traduces ATP hydrolysis to mechanical work. The different conformational states of myosin are termed strong or weak actin-binding states <ref name="risal2004"> PMID: 15184651</ref>.




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==Nucleotide binding pocket: ADP + Mg<sup>2+</sup>==
==Nucleotide binding pocket: ADP + Mg<sup>2+</sup>==


The nucleotide-binding pocket is located at the interface of the 50 kDa upper subdomain and the N-terminal subdomain <ref>PMID: 15184651</ref>, which is opposite to a deep cleft that bisects the actin-binding domain (Fig. 3).This part of protein involves an arrangement of a secondary structure mainly around the parallel 7-stranded <scene name='57/579700/Strands/1'> β-sheet</scene>. Loops extending from the &beta;-strands interact with the adenine nucleotide.  
The nucleotide-binding pocket is located at the interface of the 50 kDa upper subdomain and the N-terminal subdomain <ref name="risal2004"> PMID: 15184651</ref>, which is opposite to a deep cleft that bisects the actin-binding domain (Fig. 3).This part of protein involves an arrangement of a secondary structure mainly around the parallel 7-stranded <scene name='57/579700/Strands/1'> β-sheet</scene>. Loops extending from the &beta;-strands interact with the adenine nucleotide.  




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[[Image:Myosin turn.png|450px|right|thumb| Figure 5. Arrows in the upper figure show the direction of rotation of the 50-kDa lower and upper subdomains and the converter around the N-terminal subdomain. Lower picture shows the pivots around which SH1 unwinds. (Himmel 2002)]]
[[Image:Myosin turn.png|450px|right|thumb| Figure 5. Arrows in the upper figure show the direction of rotation of the 50-kDa lower and upper subdomains and the converter around the N-terminal subdomain. Lower picture shows the pivots around which SH1 unwinds. (Himmel 2002)]]
The 50-kDa upper and lower subdomains as well as the converter control the motor function of the myosin head by rotating around the N-terminal subdomain (Fig 5). The rotations depend on the conformational changes of the 3 joints; switch II, SH1 helix region, and relay. <ref>PMID: 15184651</ref> The joints work together in the transition between the different conformational states of MD to control the overall organization of the myosin head.  They also allow communication between the nucleotide-bonding pocket, acting-binding interface and the lever arm <ref name="houdusse2000"> PMID: 11016966</ref>.
The 50-kDa upper and lower subdomains as well as the converter control the motor function of the myosin head by rotating around the N-terminal subdomain (Fig 5). The rotations depend on the conformational changes of the 3 joints; switch II, SH1 helix region, and relay <ref name="risal2004"> PMID: 15184651</ref>. The joints work together in the transition between the different conformational states of MD to control the overall organization of the myosin head.  They also allow communication between the nucleotide-bonding pocket, acting-binding interface and the lever arm <ref name="houdusse2000"> PMID: 11016966</ref>.


Switch II, a catalytic loop of the nucleotide-binding pocket, moves in and out of the nucleotide-binding pocket during enzymatic activity. It is responsible for the unwinding of SH1 helix, along with the conformational changes caused by nucleotide binding. As SH1 unwinds, by rotating around two pivots (G695, G706, Fig. 5), it uncouples the converter/lever module from the MD <ref>PMID: 12297624</ref>. Movement of the converter is controlled by the relay joint. The converter/relay module attains different conformations changing the position of the lever arm (Fig. 4) and thus giving rise to the different states in the actomyosin cycle <ref name="houdusse2000"> PMID: 11016966</ref>.
Switch II, a catalytic loop of the nucleotide-binding pocket, moves in and out of the nucleotide-binding pocket during enzymatic activity. It is responsible for the unwinding of SH1 helix, along with the conformational changes caused by nucleotide binding. As SH1 unwinds, by rotating around two pivots (G695, G706, Fig. 5), it uncouples the converter/lever module from the MD <ref>PMID: 12297624</ref>. Movement of the converter is controlled by the relay joint. The converter/relay module attains different conformations changing the position of the lever arm (Fig. 4) and thus giving rise to the different states in the actomyosin cycle <ref name="houdusse2000"> PMID: 11016966</ref>.
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Taking part in the organization of the different conformations of the contractile cycle is also the so called switch I, which is a second catalytic loop of the nucleotide-binding pocket. <ref name="houdusse2000"> PMID: 11016966</ref> Switch II forms a specific salt bridge and hydrogen bond interactions with switch I that stabilize the pre-power stroke state  <ref>PMID: 12297624</ref>.
Taking part in the organization of the different conformations of the contractile cycle is also the so called switch I, which is a second catalytic loop of the nucleotide-binding pocket. <ref name="houdusse2000"> PMID: 11016966</ref> Switch II forms a specific salt bridge and hydrogen bond interactions with switch I that stabilize the pre-power stroke state  <ref>PMID: 12297624</ref>.


In the pre-power stroke conformation of the MD, switch II interacts with the nucleotide-binding pocket and forms the stabilizing hydrogen bond interactions and a salt bridge with switch I. <ref>PMID: 12297624</ref><ref>PMID: 15184651</ref> Rotation of the 50-kDa upper subdomain away from the N-terminal subdomain pulls switches I and II apart breaking the protein- nucleotide interactions between switch I and ADP, as well as changing the conformation of switch II. These changes result in closing of the actin-binding site and opening of the nucleotide-binding pocket, leading to MgADP release. At the same time SH1 helix is unwound and the lever arm is able to change its position enabling sliding of myosin through the actin filament <ref>PMID: 12297624</ref>.
In the pre-power stroke conformation of the MD, switch II interacts with the nucleotide-binding pocket and forms the stabilizing hydrogen bond interactions and a salt bridge with switch I <ref>PMID: 12297624</ref><ref name="risal2004"> PMID: 15184651</ref>. Rotation of the 50-kDa upper subdomain away from the N-terminal subdomain pulls switches I and II apart breaking the protein- nucleotide interactions between switch I and ADP, as well as changing the conformation of switch II. These changes result in closing of the actin-binding site and opening of the nucleotide-binding pocket, leading to MgADP release. At the same time SH1 helix is unwound and the lever arm is able to change its position enabling sliding of myosin through the actin filament <ref>PMID: 12297624</ref>.




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