Sandbox 154: Difference between revisions

[[Image:Actin filament atomic model.png|thumb|F-Actin; surface representation of 13 subunit repeat based on Ken Holmes' actin filament model]]

F-actin has the appearance of two right-handed helices, with a gradual twist around one another. It is actually composed of repeats of 13 actin units for every 6 left-handed turns, spanning a length of 350 Å<ref name="Holmes2"/>. Including the ADP and Ca²⁺, the F-actin molecule as shown here consists of 377 residues (43kDa), two major domains separated by a nucleotide-binding cleft<ref name="oda" />. Depending on the state of the bound nucleotide, the most stable conformation of F-actin changes. In its ATP and ADP + Pi nucleotide bound states, it has a closed binding cleft. In its ADP only bound state, it has a wider binding cleft<ref name="Pfaendtner"/>A characteristic trait of actin is that the domains remain twisted relative to one another, despite the nucleotide-state-dependent conformational changes<ref name="oda" />.