molecular motors

what does a motor do?

a motor converts energy into mechanical work or motion

what kind of molecular motors are there in biology + example for each

• linear motors → Myosin, cytoskeleton motor proteins

• rotational motors → F0F1-ATPase

How can energy be transformed into force per 1 nm?

divide energy by 10-9 m

How does ATP hydrolysis lead to motion?

ATP hydrolyse → small conformational change in motor domain → amplified and translated into movement

Why does nature need molecular motors?

transporting vesicles with polymerization of filaments is inefficient

How many filaments would you need to transport a vesicle R = 50 nm, viscousity = 40 pas with a velocity of 1 micrometer/s? Calculation (chemical potential of polymerization ~ 8kT, length per monomer 2.9 nm)

Stoke’s Law

Structure of Myosin II

• 2 heavy chains

  • motor domain with ATP binding site

  • rod-like tail region

• 2 light chains

  • wrapped around neck region

  • similar to calmodium

Steps in mysosin-actin cycle

FRET (definition, and formula for FRET efficiency, Föster radius

• Fluorescence resonance energy transfer

• if donor and acceptor are close together the energy is transfered and the acceptor releases a fluorophore

• the efficiency decreases with the distance r between the acceptor and donor

• the föster radius is the radius at which the efficiency = 0.5

What is another experimental approach to look at the mechanics of actin-myosin?

• in vitro motility assay

• mysoin is bound to substrate (immobilized) → watch how fluorescence labeled actin filaments are displaced

Processive vs non-processive motors

non-processive motor:

→ motor undergoes only one kick before it detatches (released)

processive motor:

→ motor undergoes many consecutive steps along filament

Formula for processive and non-processive motors

what is an important measure for this? Formula

duty ratio r

Example for non-processive motor and processive motor

non-processive: myosin II

processive: Kinesin (speed independent from kinesin density)

How does the F0F1-ATPase work?

• takes 1/3 rotational steps and converts el.mechanical energy into chemical energy (ATP)

• driven by proton gradient

• almost 100% energy efficiency