Share This

CHAMPAIGN, Ill. -- Scientists have developed an extremely accurate imaging technique for looking inside the machinery of a cell and have found that molecules of myosin "walk" in a fashion very much like a human.

Related Articles

"Myosin walks like we walk, but with a 74-nanometer stride that is more than 10 million times smaller than ours," said Paul Selvin, a professor of physics at the University of Illinois at Urbana-Champaign and corresponding author of a paper to appear in the journal Science, as part of the Science Express Web site, on June 5.

Myosin is a tiny molecular motor that converts chemical energy into mechanical motion. While there are more than a dozen types of myosin (including myosin II – the main protein responsible for muscle contractions), Selvin and his collaborators studied myosin V.

"This protein is also responsible for movement," Selvin said, "But not muscular movement. Myosin V is a little cargo transporter in our cells that moves things around by stepping along filaments of actin."

Myosin V is particularly prevalent in nerves. For this reason, mutations in the protein can lead to seizures and other neurological problems. "Like many other biomolecular motors, Myosin V is amazing," Selvin said. "It's tiny, but strong. It can carry more than 1,000 times its own weight."

Myosin V has two "legs" connected to a "body," but exactly how the protein molecule moves its load along helical fibers of actin has been a mystery. "Studies have suggested two main models for movement," Selvin said. "One is the hand-over-hand (or foot-over-foot) 'walking' model in which the two feet alternate in the lead. The other model is the 'inchworm' model in which one foot always leads."

The two models predict significantly different step sizes, Selvin said, but previous imaging techniques have lacked the resolution necessary to measure the step size and determine which model is correct. To measure such minuscule motion, Selvin and his Illinois colleagues -- physics professor Taekjip Ha and graduate students Ahmet Yildiz and Sean McKinney -- developed a single-molecule imaging technique that is capable of locating the position of a fluorescent dye to within 1.5 nanometers. (One nanometer is a billionth of a meter, or about 10,000 times smaller than the width of a human hair). This localization represents a 20-fold improvement over other techniques that use fluorescent dyes.

The researchers also found a way to extend the lifetime of the dye from a few seconds to several minutes. Then they teamed up with physiology professor Yale Goldman and postdoctoral researcher Joseph Forkey, both at the University of Pennsylvania, in applying the technique to measuring myosin movement.

"First, we attach a little fluorescent dye to one of the feet and we take a picture with a digital camera attached to a microscope to find exactly where the dye is," Selvin said. "Then we feed the myosin a little food called adenosine triphosphate, and it takes a step. We take another picture, locate the dye, and accurately measure how far the dye moved."

By looking at the step size, the scientists can tell whether the protein is walking or inchworming along, Selvin said. If it is walking, the rear foot takes twice as big a step than if it were inchworming.

"The long dye lifetime allowed us to measure many consecutive steps, which occurred about once every 3 seconds," Selvin said. "The foot wearing the dye would move forward 74 nanometers, then pause while the unlabeled foot moved forward. The cycle would then repeat itself. The 74-nanometer step size we measured is consistent with a hand-over-hand walking mechanism and inconsistent with an inchworm mechanism."

As an additional check, the researchers also labeled the myosin higher up on the leg, "somewhere in the neighborhood of the thighbone," Selvin said. "The steps alternated in size between long and short, just as you'd expect if it was walking. An inchworm motion, on the other hand, would always yield the same step size, and so we could rule that out."

There are hundreds of different types of biomolecular motors, involved in everything from muscle contraction to moving chromosomes during cell division, to reloading necessary ammunition within nerve cells so they can repeatedly fire. "The cell is a busy place, much like a city where things are constantly moving around," Selvin said. "It will be interesting to see whether all the motors move in the same way."

The work was funded by the National Institutes of Health, the National Science Foundation, the U.S. Department of Energy and the Carver Trust foundation.

University Of Illinois At Urbana-Champaign. "Myosin Molecule Walks Like A Person, Experiment Shows." ScienceDaily. ScienceDaily, 11 June 2003. <www.sciencedaily.com/releases/2003/06/030611082254.htm>.

University Of Illinois At Urbana-Champaign. (2003, June 11). Myosin Molecule Walks Like A Person, Experiment Shows. ScienceDaily. Retrieved March 31, 2015 from www.sciencedaily.com/releases/2003/06/030611082254.htm

University Of Illinois At Urbana-Champaign. "Myosin Molecule Walks Like A Person, Experiment Shows." ScienceDaily. www.sciencedaily.com/releases/2003/06/030611082254.htm (accessed March 31, 2015).

Mar. 31, 2015  Increasing state alcohol taxes could prevent thousands of deaths a year from car crashes, say researchers, who found alcohol-related motor vehicle crashes decreased after taxes on beer, wine and ... full story

Mar. 31, 2015  Alcoholism takes a toll on every aspect of a person's life, including skin problems. Now, a new research report helps explain why this happens and what might be done to address it. "The clinical ... full story

Mar. 31, 2015  A new population of 'memory' immune cells has been discovered by scientists, throwing light on what the body does when it sees a microbe for the second time. This insight, and others like it, will ... full story

Mar. 31, 2015  Coronary heart disease and stroke, two of the leading causes of death in the United States, are diseases associated with heightened platelet reactivity. A new study in humans suggests an underlying ... full story

Mar. 31, 2015  A new study had researchers seeking answers to why the therapeutic benefit afforded by SSRIs was so limited in children and teenagers. If researchers can uncover the biological mechanisms preventing ... full story

Mar. 31, 2015  A drug being developed to treat osteoporosis may also be useful for treating osteogenesis imperfecta or brittle bone disease, a rare but potentially debilitating bone disorder that that is present ... full story

Mar. 31, 2015  It is possible to quantify and classify the effects of different diseases on the activity of intestinal bacteria, new research demonstrates for the first time. Human intestinal flora, known as ... full story

Mar. 31, 2015  During prenatal development, the brains of most animals, including humans, develop specifically male or female characteristics. But scientists have known little about the details of how this ... full story

Mar. 31, 2015  A history of depression may put women at risk for developing diabetes during pregnancy, according to research. This study also pointed to how common depression is during pregnancy and the need for ... full story

Featured Videos

Solitair Device Aims to Takes Guesswork out of Sun Safety

Reuters - Innovations Video Online (Mar. 31, 2015)  The Solitair device aims to take the confusion out of how much sunlight we should expose our skin to. Small enough to be worn as a tie or hair clip, it monitors the user&apos;s sun exposure by taking into account their skin pigment, location and schedule. Matthew Stock reports.
Video provided by Reuters

Soda, Salt and Sugar: The Next Generation of Taxes

Washington Post (Mar. 30, 2015)  Denisa Livingston, a health advocate for the Dinι Community Advocacy Alliance, and the Post&apos;s Abby Phillip discuss efforts around the country to make unhealthy food choices hurt your wallet as much as your waistline.
Video provided by Washington Post

S. Leone in New Anti-Ebola Lockdown

AFP (Mar. 28, 2015)  Sierra Leone imposed a three-day nationwide lockdown Friday for the second time in six months in a bid to prevent a resurgence of the deadly Ebola virus. Duration: 01:17
Video provided by AFP

Related Stories

July 19, 2012  Scientists are bringing the basis of muscle movement into sharper focus. Muscle contraction and many other movement processes are controlled by the interplay between myosin and actin filaments. Two ... full story

Apr. 19, 2011  New insight into the physiology of cardiac muscle may lead to the development of therapeutic strategies that exploit an inherent protective state of the heart. The research discovers a state of ... full story

Apr. 11, 2011  More than 200 years ago, Luigi Galvani discovered that the muscles of a frog's leg twitch when a voltage is applied. Scientists from Italy, the UK and France have brought this textbook classic ... full story

Aug. 25, 2010  Scientists have discovered a mechanism that plays a critical role in the formation of long-term memory. The findings shed substantial new light on aspects of how memory is formed, and could lead to ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.