White Cyto 2 Flashcards
Actin accessory proteins have three types of affects. What are they?
- Affect actin subunits.
- Affect actin filaments.
- Affects filament bundling, cross linking, and attachment to membranes.
The four proteins that affect actin SUBUNITS are?
What are their functions?
- ARP Complex: nucleates assembly of weblike, highly branched chains. Associated with (-) end.
- Formin: nucleates assembly of long, UNBRANCHED chains. Associated with (+) end.
- Thymosin: binds actin subunit/monomer, prevents assembly.
- Profilin: binds actin subunit/monomer, promotes assembly by speeding elongation.
The ARP complex consists of two Arp proteins, ___ and ___.
When the complex binds to an activation factor, inducing a conformational change, the complex mimics what end of actin?
This is a FAST process because it bypasses the rate-limiting step of actin growth, which is what?
Arp2 and Arp3.
(+) end.
rate-limiting step = filament nucleation.
The reason why Listeria can move around so fast in a cell utilizing actin filaments is because of this protein, which does what?
ActA.
ActA is another activating factor of the ARP Complex, allowing nucleation and growth of actin filaments.
What actin filament structure allows the most efficient functioning of the ARP complex?
ARP is most efficient when bound to the side of a preexisting actin filament, cross-linked at 70 degree angle.
The ARP Complex and Formins help regulate cell movement by forming these two types of cell projections…
Lamellipodia: flat, protrusive veils.
Microvilli/filopodia: long, spiky bundles.
The formin protein has a ____ structure. Each formin subunit binds ____, at this end, ___, of the actin filament.
dimeric.
each subunit binds one actin monomer, therefore the formin dimer captures two monomers.
(+) end, or growing end.
This protein keeps actin polymers available for actin polymerization. How does it do this?
The result of thymosin binding with actin monomer is what?
Thymosin.
By keeping actin monomer SOLUBLE, thymosin allows the monomer to be readily available for generating filaments.
Thymosin bound to actin monomer results in no growth of actin filament.
This protein binds to actin monomers, recruiting them to the actin filament for polymerization.
The result of profilin binding to actin monomer results in what?
Profilin.
Profilin binding results in rapid growth of actin filament.
Name the five proteins that affect actin FILAMENTS.
Which ones stabilize the actin filament?
Which ones are involved in disassembly?
- Tropomodulin
- Tropomyosin
- Capping protein
- Cofilin
- Gelsolin
Stabilize: Tropomodulin, tropomyosin, capping protein.
Disassembly: Cofilin, Gelsolin.
What does Tropomodulin do?
Prevents assembly/disassembly at (-) end. This stabilizes the actin filament (muscles).
What does Tropomyosin do?
Stabilizes filament by preventing binding with other proteins.
What does Capping protein do?
What protein serves this same function, but at the other end of capping protein?
Prevents assembly/disassembly at (+) end by reducing the rate of polymerization and depolymerization.
Tropomodulin also prevents assembly/disassembly, but at (-) end.
What does Cofilin, also known as ____, do?
What protein could be considered to have the opposite function of cofilin?
Cofilin is also called Actin Depolymerizing Factor.
Cofilin finds to ADP-actin filaments and disassembles filaments by forcing the filament to twist tightly, weakening contact points between actin subunits.
Tropomyosin stabilizes while cofilin disassembles.
What does Gelsolin do?
What end does Gelsolin bind to?
Gelsolin severs actin filaments, making smaller filaments available for elongation or disassembly.
Gelsolin binds to (+) end.
What 5 proteins are involved with actin filament bundling, cross-linking, and membrane attachment?
- alpha-actinin
- Fimbrin
- Filamin
- Spectrin
- ERM Family
Actin filaments come together in two types of organization. What are they and what proteins are associated with each structure?
Bundle: parallel, cross-linked array of either alpha-actinin or fimbrin.
Web-like organization (also called gel-like): creates a looser meshwork and the actin filaments are held together by filamin.
Compare/contrast alpha-actinin, fimbrin, filamin.
alpha-actinin: cross-links actin filaments into LOOSE bundles. allows myosin-II entry.
fimbrin: cross-links actin filaments into TIGHT bundles. does NOT allow myosin-II entry.
* you usually find alpha-actinin OR fimbrin, mostly based on function.
filamin: loose, highly viscous, gel-like networks. Cells require actin gel to extend membrane/crawl on solid surface.
What two proteins attach the cytoskeleton to the membrane? Describe their function
Spectrin and ERM Family.
Spectrin: attaches actin to plasma membrane. RBC stability/durability. (Defective Spectrin = hemolytic anemia or Hereditary Spherocytosis (HS)).
ERM: mediates attachment of actin to plasma membrane. Two attachment points on ERM: actin filament and transmembrane protein.
Accessory proteins that control assembly and position of cytoskeletal filaments fall into what three major groups?
- tubulin dimers
- microtubules
- filament cross linking
Describe the three proteins that are associated with tubulin dimers.
Stathmin: binds subunits, prevents assembly.
TIPS: plus-end tracking proteins that stay on growing plus end. can attach to membranes.
gamma-TuRC: responsible for nucleation of MT growth.
remains associated with minus end.
What location do microtubules nucleate from and what protein is attached to it? In animal cells, this is also known as what?
microtubule-organizing center (MTOC), and gamma-TuRCs are attached to MTOC, also known as the centrosome in animal cells.
What end of microtubules, + or -, is attached to the centrosome?
minus ends attached to centrosome, via gamma-TuRCs. plus ends point outward away from centrosome.
What 4 proteins are involved with regulation of stability of MT filaments?
- Katanin (“sword” severs MTs)
- MAPs
- XMAP215
- Kinesin 13
