By Jzp706 (Own work) [CC0], via Wikimedia Commons https://commons.wikimedia.org/wiki/File%3AKinesin_walking.gif
Have you ever wondered how tiny motor proteins manage to carry cargo inside cells?
As we know, motor proteins called kinesins transform energy from chemical ATP into mechanical action by attaching themselves to large cargoes like mitochondria and pulling them along cytoskeletal filaments. Each kinesin contains two “head” subunits, and each subunit contains two binding sites – one to grip and walk along microtubules and the other to bind ATP. However, few studies have been conducted on motor proteins’ detailed mechanisms.
Recently, Rice University led a study exploring the little-understood topic of the sensitivity of a motor’s velocity in response to a force and the cooperation between motor proteins. The researchers used computer simulations to provide the first molecular-level details of how kinesins respond to external forces. The models showed that the velocity of kinesins is weakly influenced by small to midrange external force but is steeply reduced by a large force: only under large loading forces would the velocity of kinesin be significantly reduced as the motor head releases ATP at a fast rate. Under small to midrange forces, the velocity barely changes.
What’s interesting to note is that the study also confirmed while motor proteins naturally work in teams, two load-bearing kinesins are not able to equally share the load unless they are within the distance of 48 nanometers from each other! As a consequence of such weak cooperation, the trailing kinesin faces the challenge of catching up to the leading one, while the lead kinesin has to take on the responsibility of carrying more than 90 percent of its cargo load. This is because, according to the researching, “the lead kinesin pays more attention to the pull of the cargo itself, which triggers a ‘switch’ in the neck linker that controls the speed. A trailing kinesin that’s too far away doesn’t sense the force and therefore can’t contribute its muscle.”
The study gives an opportunity for future study of similar mechanisms, such as that of dyneins, larger and more complex proteins that move cargo within cells. It also inspires more scientists to research kinesins as defective or deficient kinesins are implicated in certain kidney diseases and Charcot-Marie-Tooth disease.
By Boumphreyfr (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons