motor proteins

What are motor proteins?

Proteins that use energy from ATP hydrolysis to move along cytoskeletal filaments

What is the main job of motor proteins?

To produce movement and transport substances within cells

What type of transport is movement of materials inside the cell called?

Intracellular transport

What acts as the tracks for motor proteins?

The cytoskeleton

What acts as the fuel for motor proteins?

ATP

What can act as cargo for motor proteins?

Vesicles and organelles and other intracellular substances

What energy conversion occurs in motor proteins?

Chemical energy from ATP is converted into mechanical energy

What does ATP hydrolysis provide to motor proteins?

Energy for movement

What does ATP hydrolysis cause in a motor protein?

A conformational change that produces movement

What is a conformational change?

A change in the shape of a protein

How do motor proteins move along their tracks?

They repeatedly bind and change shape and release and reset and bind again

How does a motor protein move overall?

One step at a time along a cytoskeletal filament

What are examples of organelles transported by motor proteins?

Mitochondria and Golgi and secretory vesicles

What major processes involve motor proteins?

Intracellular transport and muscle contraction and cell division and cell motility

How do motor proteins contribute to cell division?

They help with chromosome separation and cytokinesis

How do motor proteins contribute to cell motility?

They help produce movements such as ciliary and flagellar movement

What three things can distinguish different motor proteins?

Their filament track and direction of movement and cargo

What are the three major motor protein families?

Myosin and kinesin and dynein

What cytoskeletal track does myosin use?

Actin filaments

What is another name for actin filaments?

Microfilaments

What cytoskeletal track does kinesin use?

Microtubules

What cytoskeletal track does dynein use?

Microtubules

What is the usual direction of myosin?

Toward the plus end of actin

What is the usual direction of conventional kinesin?

Toward the plus end of microtubules

What direction does dynein move?

Toward the minus end of microtubules

Which motor protein family moves on actin?

Myosin

Which two motor protein families move on microtubules?

Kinesin and dynein

What does it mean that actin and microtubules are polarized?

They have structurally different plus and minus ends

What are the two ends of a polarized cytoskeletal filament?

Plus end and minus end

What determines the direction a motor protein moves?

The structure of its motor domain and the polarity of its track

What is the motor domain also called?

The head

What does the head of a motor protein bind?

The cytoskeletal filament and ATP

What does the motor protein head determine?

The track and direction of movement

What part of a motor protein links it to cargo?

The tail with associated adaptor proteins

What does the motor protein tail determine?

Cargo specificity

What is an adaptor protein in motor protein transport?

A protein that helps connect the motor to its cargo

What happens if the cargo binding tail is defective?

Cargo transport can fail even if the motor domain still works

What is the easiest way to remember motor protein structure?

Head equals movement and tail equals cargo

What determines the biological role of an individual motor protein?

Its cargo specificity helps determine its biological role

What is the mechanochemical cycle of motor proteins?

Filament binding then shape change then release then relaxation then rebinding

What is the basic relationship between ATP and motor movement?

ATP hydrolysis drives conformational changes that create mechanical movement

What are the main types of myosin in these notes?

Myosin I and Myosin II and Myosin V and Myosin VI

What direction do most myosins move?

Toward the plus end of actin

What is the important directional exception among myosins?

Myosin VI

What direction does Myosin VI move?

Toward the minus end of actin

What is Myosin II best known for?

Muscle contraction

What are the major functions of Myosin II?

Muscle contraction and cytokinesis and cell migration

What is the structure of Myosin II?

Two heavy chains with two copies of each of two light chains and a long coiled coil tail

How many heavy chains does Myosin II have?

Two heavy chains

What forms the globular heads of Myosin II?

The N terminal regions of the heavy chains

What is found in the Myosin II globular head?

The force generating motor machinery

What does the long coiled coil of Myosin II do?

It allows the heavy chains to dimerize

What do Myosin II tails form when they associate with other Myosin II molecules?

Bipolar thick filaments

What is a bipolar thick filament?

A filament with myosin heads oriented in opposite directions at its two ends

What does each Myosin II head do?

It binds and hydrolyzes ATP and moves toward the plus end of actin

Why are Myosin II thick filaments effective at sliding actin filaments?

Their heads are oriented in opposite directions

What is the thick filament in muscle mainly made from?

Myosin II

What is the thin filament in muscle mainly made from?

Actin

What happens to actin and myosin during muscle contraction?

They slide past each other

What happens to the sarcomere during muscle contraction?

It shortens

Do actin filaments themselves shorten during muscle contraction?

No

Do myosin filaments themselves shorten during muscle contraction?

No

If actin and myosin do not shorten then how does the sarcomere shorten?

The filaments slide past each other

What provides the energy for actin myosin sliding?

ATP hydrolysis

What is cytokinesis?

The physical separation of one dividing cell into two daughter cells

Which motor protein is important in cytokinesis?

Myosin II

What structure does Myosin II help form during cytokinesis?

The contractile ring

What does the contractile ring do?

It contracts and helps pinch one cell into two daughter cells

Is Myosin II found only in muscle cells?

No

What does Myosin II do in nonmuscle cells?

It contributes to contraction and cytokinesis and cell migration

How can Myosin II activity be regulated?

By phosphorylation

What does MLCK stand for?

Myosin light chain kinase

What does MLCK phosphorylate?

The regulatory light chain of Myosin II

What effect does MLCK phosphorylation have on Myosin II?

It promotes the active extended form and bipolar filament assembly and contraction

What processes are supported by Myosin II regulatory light chain phosphorylation?

Stress fiber contraction and cytokinesis

What is Myosin I structurally?

A one headed monomeric myosin

How many heavy chains does Myosin I have?

One heavy chain

How is the Myosin I motor domain related to Myosin II?

It has a similar motor domain but a different tail

What special binding ability can the Myosin I tail have?

A second actin binding site or a membrane binding site

What direction does Myosin I move?

Toward the plus end of actin

What are the main functions of Myosin I?

Intracellular organization and membrane actin interactions

What surface process is Myosin I involved in?

Protrusion of actin rich structures at the cell surface

What is Myosin V structurally?

A two headed myosin with a dimeric design similar to Myosin II

What direction does Myosin V move?

Toward the plus end of actin

What is the main function of Myosin V?

Cargo transport

What does Myosin V transport?

Vesicles and organelles

What is an example of cargo transported by Myosin V?

Melanosomes

What is the easiest association for Myosin V?

Myosin V equals vesicle and organelle transport on actin

What is Myosin VI structurally?

A two headed myosin

What is the main function of Myosin VI?

Cargo transport

What makes Myosin VI unusual?

It moves toward the minus end of actin

What is the easiest way to remember Myosin VI?

Myosin VI is the reverse direction myosin

Which myosin is the major exception to the usual plus end direction?

Myosin VI

What is conventional kinesin?

An ATP powered motor protein that moves along microtubules

What direction does conventional kinesin move?

Toward the plus end of microtubules

What is the structure of conventional kinesin?

Two heavy chains and two light chains with two globular heads and a coiled coil region

How many heavy chains does conventional kinesin have?

Two

How many light chains does conventional kinesin have?

Two

How many globular motor heads does conventional kinesin have?

Two

What is the purpose of the kinesin coiled coil?

Heavy chain dimerization