Helix-turn-Helix

Two helices are connected by a small loop or turn

These helices are stabilized by non-polar contacts between the helices

Mostly found in DNA binding proteins, directly involved in DNA binding

Generally consists of 20 amino acids

Second helix is involved in DNA binding, enters in major groove of the target site

TLS Online TPP Program

#Id: 1381

#Unit 4. Cell Communication and Cell Signaling

At steady state, ATP–G-actin subunits add preferentially to the (+) end, while ADP–G-actin subunits disassemble from the (−) end, giving rise to treadmilling of subunits.

TLS Online TPP Program

#Id: 1382

#Unit 4. Cell Communication and Cell Signaling

Profilin enhances the exchange of ADP for ATP on G-actin. Cofilin enhances the rate of loss of ADP-actin from the filament (−) end. Thymosin-β4, binds to ATP–G-actin in such a way that it inhibits addition of the actin subunit to either end of the filament.

TLS Online TPP Program

#Id: 1383

#Unit 4. Cell Communication and Cell Signaling

Formin protein nucleate the assembly of unbranched filaments, (FH1 and FH2 domains-Actin nucleation by the formin FH2 domain).

Formins are activated by membrane-bound Rho-GTP, a Ras-related small GTPase.

The Arp2/3 Complex Nucleates Branched Filament Assembly.

TLS Online TPP Program

#Id: 1384

#Unit 4. Cell Communication and Cell Signaling

Toxins affect the dynamics of actin polymerization; some, 

Latrunculin

Phalloidin

Cytochalasin D

Jasplakinolide

TLS Online TPP Program

#Id: 1385

#Unit 4. Cell Communication and Cell Signaling

There are three classes of myosins, are present in many eukaryotes: 

Myosin I- single head domain

Myosin II- two heads and assembles into bipolar filaments

Myosin V- two heads but does not assemble into filaments

TLS Online TPP Program

#Id: 1386

#Unit 4. Cell Communication and Cell Signaling

The length of the myosin II neck domain determines the rate of movement.