How molecular transports change gear: Environment determines the motion of motor proteins

Dec 21, 2012
As the molecular load on myosin-V increases, lever-arm swing motion (left) switches to Brownian search-and-catch (right). Credit: 2012 Toshio Yanagida, RIKEN Quantitative Biology Center

The motor protein myosin-V, which hauls molecular cargoes around cells by ratcheting along filaments of actin, switches between two different molecular mechanisms of movement depending on the environment. This finding by a research group led by Toshio Yanagida of the RIKEN Quantitative Biology Center, Osaka, and Osaka University, could form the basis for designing energy-saving artificial nano-motors.

Previous work by other researchers showed that myosin-V typically uses the two mechanisms—lever-arm swing and Brownian search-and-catch—alternately to propel itself along a filament hand-over-hand. Myosin-V possesses two arm-like projections, the heads of which bind to actin. When myosin-V links to the molecule adenosine triphosphate (ATP) the rear head detaches from the actin filament. As ATP releases energy by losing a phosphate, the front head then goes through a lever-arm swing motion pulling forward on the filament like an oar through water, dragging the rear projection with it. The rear head then swings over and forward while buffeted by passing molecules in random . As it nears the filament in front, it catches onto it.

Yanagida and his colleagues, including Keisuke Fujita and Mitsuhiro Iwaki, were able to attach a fluorescent polystyrene bead to the rear projection of myosin-V with a strand of DNA. This allowed them to measure the motions of the motor molecule accurately by tracking the displacement of the bead. They could also measure the force each head exerted by trapping the bead and holding it steady using the laser light mechanism known as under different loads and environmental conditions.

The results showed that for low loads along filaments where there are no obstacles, the bulk of the work of myosin-V's motion is executed by the lever-arm swing mechanism. But at higher loads, and in less predictable environments, the force capable of being exerted by lever-arm swing reaches a maximum and Brownian search-and-catch motion automatically takes over. Cells contain a meshwork of crisscrossing actin filaments and there is always the possibility of colliding with moving molecules and vesicles to hinder the transport of myosin-V's molecular cargoes. Under these circumstances the 'high-stepping' Brownian search-and-catch motion comes into its own.

"We are hopeful that the studies of other biological actuators or simulations will show that our theory for myosin-V movement is universal and therefore adds a much more concrete paradigm to the design of artificial nano-machines," says Yanagida.

Explore further: Scientists unlock secrets of protein produced by disease-causing fungus

More information: Fujita, K., Iwaki, M., Iwane, A.H., Marcucci, L. & Yanagida, T. Switching of myosin-V motion between the lever-arm swing and Brownian search-and-catch. Nature Communications 3, 956 (2012). www.nature.com/ncomms/journal/v3/n7/full/ncomms1934.html

add to favorites email to friend print save as pdf

Related Stories

Biophysics: Order in chaos

May 03, 2012

The process of skeletal muscle contraction is based around protein filaments sliding inside sarcomeres — the structural units of muscle fiber. Inside each sarcomere is a set of filament motors, which ...

Recommended for you

For cells, internal stress leads to unique shapes

1 hour ago

From far away, the top of a leaf looks like one seamless surface; however, up close, that smooth exterior is actually made up of a patchwork of cells in a variety of shapes and sizes. Interested in how these ...

Adventurous bacteria

2 hours ago

To reproduce or to conquer the world? Surprisingly, bacteria also face this problem. Theoretical biophysicists at Ludwig-Maximilians-Universitaet (LMU) in Munich have now shown how these organisms should ...

Revealing camouflaged bacteria

4 hours ago

A research team at the Biozentrum of the University of Basel has discovered an protein family that plays a central role in the fight against the bacterial pathogen Salmonella within the cells. The so cal ...

User comments : 0

More news stories

Chimpanzees prefer firm, stable beds

Chimpanzees may select a certain type of wood, Ugandan Ironwood, over other options for its firm, stable, and resilient properties to make their bed, according to a study published April 16, 2014 in the open-access ...

For cells, internal stress leads to unique shapes

From far away, the top of a leaf looks like one seamless surface; however, up close, that smooth exterior is actually made up of a patchwork of cells in a variety of shapes and sizes. Interested in how these ...

IBM posts lower 1Q earnings amid hardware slump

IBM's first-quarter earnings fell and revenue came in below Wall Street's expectations amid an ongoing decline in its hardware business, one that was exasperated by weaker demand in China and emerging markets.