Non-polymerizable monomeric actin: Difference between revisions

Structural changes between the ATP and ADP-bound state of <scene name='User:Thomas_E_Sladewski/Sandbox_1/10state_morph_all_activesite/1'> AP-actin </scene> are confined to the active site. The <scene name='User:Thomas_E_Sladewski/Sandbox_1/10state_morph_scene2/3'> alpha-carbon backbones </scene> of the two states outside the sensor loop region superimpose very well, with a RMSD of 0.19 angstroms. A close-up of the <scene name='User:Thomas_E_Sladewski/Sandbox_1/10state_morph_sensorloop/5'> active site </scene> reviles how binding ATP elicits structural changes in the nucleotide-binding cleft that is propagated to the sensor loop. When actin is bound to ADP, the serine-14 side chain forms a hydrogen bind with the beta phosphate ADP. Upon ATP binding, the gamma phosphate sterically clashes with the oxygen of serine-14, forcing the hydroxyl to rotate 130°. The displaced serine residue impinges on the backbone carbonyls of residues isoleucine-71 and glutamine-72 in the sensor loop. This causes a 180° rotation of the peptide linkage between glutamine-72 and histidine-73. These structural changes impact residues proximal to the sensor loop. Transition to the ATP-bound state causes glutamine-72 to form a new hydrogen bond with threonine-77. This induces a reorientation of <scene name='User:Thomas_E_Sladewski/Sandbox_1/10state_morph_sensorloop_add/2'>asparagine-78</scene>. ATP binding also disrupts hydrogen bonding between arginine-183 and residues 72 and 73 of the sensor loop causing a conformational change of <scene name='User:Thomas_E_Sladewski/Sandbox_1/10state_morph_sensorloop_add/3'>arginine-183</scene>. Aspartic acid-179 stacks against histidine-73 in the ATP-bound state which induces a shift in the position of <scene name='User:Thomas_E_Sladewski/Sandbox_1/10state_morph_sensorloop_add/4'>arginine-177 </scene> to improve salt bridge formation with aspartic acid-179. In the AP-actin structure, changes in conformation due ATP binding are local to the active site and do not appear to propagate into domains.