Kinesin and MicrotubulesKinesin and Microtubules

Molecular MotorsMolecular Motors

http://www.komsta.net/chemwalls/kinesin1-1280.jpg

http://www.itg.uiuc.edu/exhibits/gallery/pages/image-22.htm

http://mcb.berkeley.edu/labs/cande/motors.html

Microtubule Microtubule Structure and FormationStructure and Formation

Polymer of two small Polymer of two small dimersdimers

Alternating pattern of Alternating pattern of αα- and - and ββ-tubulin-tubulin

Alternation plays Alternation plays important role in important role in Kinesin movementKinesin movement

http://www.daviddarling.info/encyclopedia/M/microtubule.html

http://upload.wikimedia.org/wikipedia/commons/8/80/Microtuble.jpg

Microtubule Microtubule Structure and FormationStructure and Formation

Polymer structure Polymer structure allows for rapid allows for rapid assembly and assembly and disassemblydisassembly

Tubulin can diffuse Tubulin can diffuse rapidly throughout the rapidly throughout the cellcell Smaller tubulin can Smaller tubulin can

move more quickly move more quickly than larger than larger microtubulesmicrotubuleshttp://en.wikipedia.org/wiki/Image:Tubulin.jpg

MicrotubulesMicrotubules

Unique bonding Unique bonding structurestructure Resistant to thermal Resistant to thermal

breakage along the breakage along the strandstrand

Dynamic ends that Dynamic ends that grow and recess grow and recess rapidlyrapidly

Leads to Dynamic Leads to Dynamic InstabilityInstability

Tubulin will not Tubulin will not organize (nucleate) organize (nucleate) on their ownon their own

Require a pre-existing Require a pre-existing microtubule or a microtubule or a catalyzing proteincatalyzing protein The cell takes The cell takes

advantage of this and advantage of this and can specify where the can specify where the microtubules gomicrotubules go

MicrotubulesMicrotubules

This graph of an This graph of an experiment on tubulin experiment on tubulin show the initial lag show the initial lag phase of three to five phase of three to five minutes where the minutes where the tubulin are nucleating tubulin are nucleating into the microtubule into the microtubule basesbases

http://intl.jcb.org/cgi/reprint/101/3/755

Dynamic InstabilityDynamic Instability

GTP-Tubulin Cap

GTP-Tubulin

GDP-Tubulin

Hydrolysis

Dynamic InstabilityDynamic Instability

Hydrolysis goes faster than tubulin addition

GTP-Tubulin

GDP-Tubulin

Dynamic InstabilityDynamic InstabilityGTP-Tubulin

GDP-Tubulin

New GTP Cap

KinesinKinesin

Kinesin has two endsKinesin has two ends One end is the “tail end” One end is the “tail end”

which attaches to whatever which attaches to whatever is being transported such is being transported such as a vesicle or organelle as a vesicle or organelle

The other end has two The other end has two “heads” which attaches to a “heads” which attaches to a microtubule. These two microtubule. These two heads walk in a “hand over heads walk in a “hand over hand” fashion along the hand” fashion along the microtubulemicrotubule

http://en.wikipedia.org/wiki/Kinesin

““Hand-Over-Hand Movement”Hand-Over-Hand Movement”

First head attaches, ADP is changed to ATP First head attaches, ADP is changed to ATP ATP causes the linking region to straighten, ATP causes the linking region to straighten,

placing the second head in frontplacing the second head in front Second head attaches to microtubuleSecond head attaches to microtubule ATP in the first head is hydrolyzed into ADP ATP in the first head is hydrolyzed into ADP

and phosphate, head loses rigidity and and phosphate, head loses rigidity and detaches detaches

ATP is formed in the second head, moving ATP is formed in the second head, moving the first head in front once againthe first head in front once again

http://valelab.ucsf.edu/images/mov-procmotconvhttp://valelab.ucsf.edu/images/mov-procmotconvkinrev5.movkinrev5.mov

Each step is 8 nanometers and the Kinesin Each step is 8 nanometers and the Kinesin travels .02-2 micrometers/secondtravels .02-2 micrometers/second

http://www.fli-leibniz.de/~kboehm/Kinesin.html

http://www7.nationalacademies.org/bpa/reports_bmm-11.gif