bio- lecture 9 notes

  • actin accessory proteins
    • thymosin- binds subunits, prevents assembly
    • gelsolin- severs filaments and binds to + end
    • does not require extra energy input
    • tropomyosin- stabilizes filament
    • cofilin- binds ADP-actin filaments, accelerates disassembly
    • stabilizes actin
    • capping protein- prevents assembly and disassembly at + end
    • slows rates of both filament growth and deplymerization by inactivating + end
      • - end bound or unbound by ARP complex
    • uncapped population of filaments- growth at + and - ends
    • capped population of filaments- growth at - end only
  • microtubule accessory proteins
    • stathmin- binds subunits, prevents assembly
    • binds two tubulin heterodimers
    • enhances catastrophes
    • phosphorylation inhibits binding to tubulin
    • keeps heterodimers bent back like they’re in GDP state
    • katanin- severs microtubules
    • includes two subunits
      • smaller subunit hydrolyzes ATP and severs
      • larger subunit directs protein to centrosome
    • MAPs- stabilize tubules by binding along sides
    • like a splint or back brace
    • GTP cap on + end
      • stabilization- frequency of catastrophes suppressed and/or growth rate enhanced
      • result is longer, less dynamic microtubules
      • destabilization- frequency of catastrophes increased
      • result is shorter, more dynamic microtubules
    • catastrophe factors bind to microtubules ends and pry protofilaments apart
      • can pull off heterodimers in T state
  • bundling proteins- cross-link actin filaments into a parallel array
  • gel-forming proteins- hold two actin filaments together at a large angle to each other to create a looser meshwork
  • contractile bundle- loose packing allows myosin-II to enter bundle
    • found in stress fiber
    • binds actin filaments with distance in between
    • space for myosin-II
    • helps cell move
    • uses a-actinin
  • gel-like network found in cell cortex
    • can move back and forth
  • parallel bundle- tight packing prevents myosin-II from entering bundle
    • found in filopodium
    • uses fimbrin
  • filamin
    • contain a bent connection between the two binding domains to form filament webs
    • important to extend thin, sheet-like membrane projections- lamellipodia
    • help cell crawl across surfaces
    • attaches to gel-like network
    • gives actin structure/meshwork
  • proteins need to be activated to interact with other proteins
  • actin structures can stiffen and change the shape of the plasma membrane via the ERM protein family
  • actin specific drugs
    • phalloidin- binds and stabilizes filaments
    • from fungus
    • cytochalasin- caps filament + ends
    • swinholide- severs filaments
    • latrunculin- binds subunits and prevents their polymerization
    • extracted from sea sponge
  • microtubule specific drugs
    • taxol- binds and stabilizes microtubules
    • from bark of tree
    • colchicine, colcemid- binds subunits and prevents their polymerization
    • from flower
    • vinblastine, vincristine- binds subunits and prevents their polymerization
    • nocodazole- binds subunits and prevents their polymerization
  • motor proteins use energy derived from ATP hydrolysis to move steadily along polarized filaments
    • carry membrane-closed organelles
    • motor domain (head) identifies track and direction
    • tail region identifies cargo
  • microtubule based motors
    • kinesin
    • most walk toward + end
    • most carry binding sites for organelle or another microtubule
    • role in spindle formation and chromosome separation
    • dyneins
    • - end directed microtubule motors
    • cytoplasmic dyneins are important for vesicle trafficking and localization of golgi
    • axonemal dyneins are sliding mirotubules that drive cilia and flagella beating