Sandbox 154: Difference between revisions

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Actin is found in nearly all eukaryotic cells and is known primarily for its function as a structural and translocation protein. It also has an ATPase function, as it hydrolyzes ATP to ADP and P<sub>i</sub> and undergoes conformational changes with each hydrolysis. Actin belongs to the actin superfamily, which includes other proteins such as Hsp70(DnaK), Hsc70, and hexokinase, because of its nucelotide-dependent conformational change<ref name="Graceffa">PMID:12813032</ref>. Because of the similarity observed in ''Escherichia Coli'''s, Hsc70 and ATPase domain of actin, it is believed that the two proteins have a common ancestory<ref name="Holmes1">PMID:19158779</ref>. Prokaryotes are not known to have actin, but do however have an actin homologue, MreB, which also leads to the idea of possible common ancestory<ref name="Holmes2">PMID:2395461</ref>.

Actin occurs in two forms: globular actin (G-actin), the free monomeric units of actin, and filamentous actin (F-actin) which is the polymer form. These two forms exist in a dynamic equilibrium with one another as ATP-associated polymerization and depolymerization occur continuously within the cell.

Actin occurs in two forms: globular actin (G-actin), the free monomeric units of actin, and filamentous actin (F-actin) which is the polymer form. These two forms exist in a dynamic equilibrium with one another as ATP-associated polymerization and depolymerization occur continuously within the cell. The monomer units in the F-actin possess a form that is distinct from the free monomeric form and it is a result of that change that the more specific ATPase activity may be observed.

== Assembly ==

'''G-actin''' is the free monomeric form of actin which polymerizes to F-actin. The structures of globular and filamentous actin are distinct from one another in numerous ways, despite the fact that G-actin comprises F-actin. When the monomeric actin becomes polymerized into F-actin, the unit becomes flattened. Also, F-actin possesses ATPase function ~~where it~~ is minimal in G-actin. G-actin appears to have more <scene name='Sandbox_154/1j6z_calcium/1'>calcium ion</scene> ligands in its structure, and also has the ligand RHO as opposed to 4-methyl histidine as found in the F-actin structure.

'''G-actin''' is the free monomeric form of actin which polymerizes to F-actin. The structures of globular and filamentous actin are distinct from one another in numerous ways, despite the fact that G-actin comprises F-actin. When the monomeric actin becomes polymerized into F-actin, the unit becomes flattened. Also, F-actin possesses an ATPase function which is minimal in G-actin. G-actin appears to have more <scene name='Sandbox_154/1j6z_calcium/1'>calcium ion</scene> ligands in its structure, and also has the ligand RHO as opposed to 4-methyl histidine as found in the F-actin structure.

Sandbox 154: Difference between revisions

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@@ Line 6: / Line 6: @@
 Actin is found in nearly all eukaryotic cells and is known primarily for its function as a structural and translocation protein. It also has an ATPase function, as it hydrolyzes ATP to ADP and P<sub>i</sub> and undergoes conformational changes with each hydrolysis. Actin belongs to the actin superfamily, which includes other proteins such as Hsp70(DnaK), Hsc70, and hexokinase, because of its nucelotide-dependent conformational change<ref name="Graceffa">PMID:12813032</ref>. Because of the similarity observed in ''Escherichia Coli'''s, Hsc70 and ATPase domain of actin, it is believed that the two proteins have a common ancestory<ref name="Holmes1">PMID:19158779</ref>. Prokaryotes are not known to have actin, but do however have an actin homologue, MreB, which also leads to the idea of possible common ancestory<ref name="Holmes2">PMID:2395461</ref>.
-Actin occurs in two forms: globular actin (G-actin), the free monomeric units of actin, and filamentous actin (F-actin) which is the polymer form. These two forms exist in a dynamic equilibrium with one another as ATP-associated polymerization and depolymerization occur continuously within the cell.
+Actin occurs in two forms: globular actin (G-actin), the free monomeric units of actin, and filamentous actin (F-actin) which is the polymer form. These two forms exist in a dynamic equilibrium with one another as ATP-associated polymerization and depolymerization occur continuously within the cell. The monomer units in the F-actin possess a form that is distinct from the free monomeric form and it is a result of that change that the more specific ATPase activity may be observed.
 == Assembly ==
 <applet load='1j6z' size='200' color='black' frame='true' align='left' caption='Globular Actin (G-actin): PDB identifier [http://www.rcsb.org/pdb/explore/explore.do?structureId=1J6Z/ 1J6Z].' scene='Sandbox_154/1j6z_black/2'/>
-'''G-actin''' is the free monomeric form of actin which polymerizes to F-actin. The structures of globular and filamentous actin are distinct from one another in numerous ways, despite the fact that G-actin comprises F-actin. When the monomeric actin becomes polymerized into F-actin, the unit becomes flattened. Also, F-actin possesses ATPase function where it is minimal in G-actin. G-actin appears to have more <scene name='Sandbox_154/1j6z_calcium/1'>calcium ion</scene> ligands in its structure, and also has the ligand RHO as opposed to 4-methyl histidine as found in the F-actin structure.
+'''G-actin''' is the free monomeric form of actin which polymerizes to F-actin. The structures of globular and filamentous actin are distinct from one another in numerous ways, despite the fact that G-actin comprises F-actin. When the monomeric actin becomes polymerized into F-actin, the unit becomes flattened. Also, F-actin possesses an ATPase function which is minimal in G-actin. G-actin appears to have more <scene name='Sandbox_154/1j6z_calcium/1'>calcium ion</scene> ligands in its structure, and also has the ligand RHO as opposed to 4-methyl histidine as found in the F-actin structure.