Arp2/3, which nucleates actin polymerization, is 〈〈〈〈〈〈 abundant in lamellipodia Ap2/3 Arp2/3 complex consists of two actin-related proteins, actin-ADP Arp2 Arp3, plus 5 smaller actin-ATP proteins When activated by a nucleation promoting factor (NPF), the Arp2/3 complex binds to the side of an existing actin filament and nucleates assembly of a new actin filament The resulting branch structure is Y-shaped
When activated by a nucleation promoting factor (NPF), the Arp2/3 complex binds to the side of an existing actin filament and nucleates assembly of a new actin filament. The resulting branch structure is Y-shaped. Arp2/3 actin-ADP + actin-ATP Arp2/3, which nucleates − actin polymerization, is abundant in lamellipodia. Arp2/3 complex consists of two actin-related proteins, Arp2 & Arp3, plus 5 smaller proteins
actin-adP actin-ATP 〈〈〈〈〈〈〈 〈〈 5员 〈〈〈〈〈〈〈 formin Whereas arp2/3 nucleates formation of branched actin filament networkS, formins are proteins that nucleate formation of unbranched actin filaments, such as those in stress fibers Formins are located adjacent to the plasma membrane The actin filaments that they nucleate have their plus ends. to which actin monomers add anchored to the formin
Whereas Arp2/3 nucleates formation of branched actin filament networks, formins are proteins that nucleate formation of unbranched actin filaments, such as those in stress fibers. Formins are located adjacent to the plasma membrane. The actin filaments that they nucleate have their plus ends, to which actin monomers add, anchored to the formin. formin actin-ADP + actin-ATP − plasma membrane
(globular actin), with bound ATP, can polymerize to form actin(filamentous) G-actin-ATP may hydrolyze bound polymerization ATP→ADP+P& release P F-actin-ATP ADP release from the filament does not occur because the cleft opening is blocked F-actin-ADP ADP/ATP exchange: G-actin depolymerization can release adp bind atP which is usually present at higher G-actin-ADP concentration than AdP in the ADP/ATP exchange cytosol G-actin-ATP
G-actin (globular actin), with bound ATP, can polymerize to form F-actin (filamentous). F-actin may hydrolyze bound ATP Æ ADP + Pi & release Pi. ADP release from the filament does not occur because the cleft opening is blocked. ADP/ATP exchange: G-actin can release ADP & bind ATP, which is usually present at higher concentration than ADP in the cytosol. G-actin-ATP polymerization F-actin-ATP Pi F-actin-ADP depolymerization G-actin-ADP ADP/ATP exchange G-actin-ATP
phosphatidyl inositol (in membrane) In addition to its PIP role in generating Phospholipase c the second (Signal activated) messengers diacylglycerol and diacylglycerol IP2, PIP, formation and hydrolysis can causes Cat activates affect the actin release from er Protein Kinase c cytoskeleton E. g, regulated formation cleavage of PIP2 can affect the concentration of profilin, and hence actin polymerization, adjacent to the plasma membrane
E.g., regulated formation & cleavage of PIP 2 can affect the concentration of profilin, and hence actin polymerization, adjacent to the plasma membrane. phosphatidyl inositol (in membrane) PIP 2 Phospholipase C (signal activated) IP 3 diacylglycerol causes Ca++ activates release from ER Protein Kinase C In addition to its role in generating the second messengers diacylglycerol and IP 3, PIP 2 formation and hydrolysis can affect the actin cytoskeleton
Profilin release by pip, cleavage PIPa binds plasma profilin at the membrane cytosolIc surrace PIP2 DAG of the plasma profilin membrane ATP This prevents actin profilin-actin profilin cytosol complex interaction Signal-activated, which may bind G-actin and promote ADP/ATP PIP, hydrolysis releases profilin exchange The increase in G-actin-ATP promotes actin polymerization adjacent to the plasma membrane
Signal-activated, which may bind G-actin and promote ADP/ATP PIP 2 hydrolysis releases profilin exchange. The increase in G-actin-ATP promotes actin polymerization adjacent to the plasma membrane. PIP 2 binds profilin at the cytosolic surface of the plasma membrane. This prevents profilin-actin interaction. PIP 2 profilin actinprofilin complex IP 3 DAG plasma membrane cytosol Profilin release by PIP 2 cleavage