ABPs and MAPs

Actin binding proteins (ABPs)

• formins

• arp2/3 complex

• thymisin B4

• profilin

• cofilin

• gelsolin

• cap z

• tripomyosin

• fimbrin

• alpha-actinin

• filamin

• spectrin

• ERM proteins

Microtubule associated proteins (MAPs)

• gamma-TURC

• stathmin

• +TIPS

• kinesin 13

• katanin

• MAPs

• XMAP215

• tau

• MAP2

• plectin

Capping protein A

Specific actin-binding protein that regulates filament growth by binding to the barbed end of actin filaments, preventing further addition or loss

Cap Z

Capping protein (A) that caps to the + end

Stabilizing proteins (A)

bind along the length of filaments

ex. Tropomyosin

Severing/Depolymerizing proteins A

ex. Cofflin enhances the rate of action depolymerization by severing actin filaments and creating more minus ends

ex. Gelsolin also severs actin filaments and remains bounds to the plus end

Cross-linking proteins A

Longer, more flexible spacers usually function to arrange filaments into gel-like networks like: filamin and spectrin

Shorter, more rigid spacers tend organize filaments into aligned bundles like fimbrin and alpha-actinin

Alpha-actinin

Cross-linking proteins that crosslinks filaments into bundles that are arranged into parallel and anti-parallel arrays

Membrane-actin linker proteins A

Attach actin cytoskeleton to the plasma membrane.

ex. Ezrin act as a linker between F-actin and the integral membrane proteins (in microvilli). Spectrin also does that but focused on membrane skeleton. Dystrophin links cortical actin to muscle cell membranes.

Tubulin oligomer binding proteins M

Stathmin can bind and sequester tubulin heterodimers

Nucleating proteins M

gamma-TURC nucleates MT assembly at the centrosome

End binding proteins M

+TIPs bind to the plus ends of MRs, EB1 is a +TIP can regulate plus end dynamics and can link MTs to organelles

Severing proteins M

Katanin severs MTs and may promote depolymerization of minus ends

Depolymerizing proteins M

A subset of kinesins (Kin 13) promote MT depolymerization at the plus end by binding to and inducing protofilament curling

Polymer-binding MAPs

• stabilize MTs by binding to their sides and inhibit disassembly

• enhance assembly by stabilizing nuclei

• organize MTs inro bundles

• mediate MT interactions with other proteins

Microtubule binding domain → binds several tubulin dimiers at onve and thus helps to stabilize the polymer

Projection domain interacts MTs with other structures

MAP 2 and Tau

Responsible for organizing microtubules in neuronal axons and dendrites. Can induce axons in cells that usually dont express them

Diseases: Red blood cells (anemia)

Issue in spectrin and cell cortex

Diseases: Muscle dystrophies

Issues in dystrophin

Diseases: Alzheimer’s

Both:

• Tau hyper-phosphorylation, which reduces the binding of Tau to microtubules

• Sequestration of hyper-phosphorylated Tau into neurofibrillary tangles, which reduces the amounr of Tau available to bind microtubules