A toddler running sometimes loses footing because both feet come off the ground at the same time. Kinesin motors that move materials around in cells have the same problem, which limits how fast they can traverse a microtubule in the cell and carry cargo, according to Penn State researchers who have now seen these kinesin motors move using an unusual microscope and tagging method.
"We can now see biological processes at molecular resolution and at sub-millisecond time scales," said William O. Hancock, professor of biomedical engineering and director of the Intercollege Graduate Program in Bioengineering, Penn State.
Kinesin with vesicle is attached with two "feet" to the cell's microtubule. This is a safe and stable time period. The kinesin untethers its back foot and moves it forward. This is a vulnerable time period when the whole complex could lose its grip. Finally the loose foot attaches to the microtubule in front and the system is once again stable.
Credit: Keith Mickolajczyk / Penn State
"To understand how motors work on a nanoscale and millisecond scale we need to see how the motors are walking. We know that neurons require transport for them to grow and survive, and materials need to travel from one end (of the neuron) to the other."
Molecular motors, in this case kinesins, are little machines that use chemical energy to generate mechanical forces sufficient to carry materials through the cell. These molecules have two limbs joined together with attachment devices on the ends that researchers call "heads" but would be better thought of as "feet."
"Diseases like Alzheimer's, ALS and others, have defects in the transport process (in neurons) and it is not understood at the molecular level what defects are and how they affect transport," said Hancock. "We think roadblock proteins bind to the microtubule tracks and impede motor movement. We can measure steps at the roadblock, and hopefully it will help us understand the disease states where transport isn't working."
When a kinesin molecule moves from the center of a microtubule toward the end, it is typically carrying cargo. One "foot" attaches to the tubule and then the other back "foot" detaches, swings over and attaches. The molecules are very stable in the short moment when both "feet" are attached, but less so at the time of detachment. The coordination of attachment and release are critical in the molecule successfully walking down the tubule.
Hancock and Keith J. Mickolajczyk, doctoral candidate in bioengineering, note in a recent issue of Biophysical Journal, that "Despite its fundamental importance to the diversity of tasks that kinesins carry out in cells, no existing quantitative model fully explains how structural differences between kinesins alter kinetic rates ... to produce functional changes in processivity."
Processivity is the average number of steps the molecular motor can take before it detaches from the microtubule and another must take its place.
Mickolajczyk built the high-resolution, single-molecule microscope so that the researchers could directly see the molecular motor move. To do this, they tagged the molecule on one "foot" with a gold nanoparticle. This allowed the researchers to follow the molecule by reflecting various types of light off the gold.
The researchers found they could model the kinesin movement as a race between attachment of the forward "foot" and detachment of the rear "foot." This walking pattern is governed both by the chemical actions of energy release from adenosine triphosphate -- the biological energy storage molecule -- and the mechanical push and pull of tethering and untethering. Altering various properties of the kinesin changes the attachment and detachment rates.
Kinesins usually carry their cargo in vesicles -- balloon-like, water-filled sacs inside cells. More than one kinesin motor can haul a vesicle at a time, and the motors fall off and are replaced by other kinesin motors during the movement along the tubule. The kinesin "feet" have defined locations on the tubules at which to bind.
"Clarifying these stepping kinetics is very satisfying because these questions have been around for 20 years, but only now do we have the technology to answer them," said Hancock.
The National Institutes of Health supported this work.
A'ndrea Elyse Messer | EurekAlert!
Progress in Super-Resolution Microscopy
17.12.2018 | Julius-Maximilians-Universität Würzburg
Communication between neural networks
17.12.2018 | Albert-Ludwigs-Universität Freiburg im Breisgau
Researchers from the University of Basel have reported a new method that allows the physical state of just a few atoms or molecules within a network to be controlled. It is based on the spontaneous self-organization of molecules into extensive networks with pores about one nanometer in size. In the journal ‘small’, the physicists reported on their investigations, which could be of particular importance for the development of new storage devices.
Around the world, researchers are attempting to shrink data storage devices to achieve as large a storage capacity in as small a space as possible. In almost...
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
17.12.2018 | Studies and Analyses
17.12.2018 | Life Sciences
17.12.2018 | Power and Electrical Engineering