Biophysics: Order in chaos

May 03, 2012 By Lee Swee Heng
© fsecart

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 appear in different densities in different areas. Scientists previously thought that the motor force would change according to the filament load in the muscle, but recent studies have shown that the motor force actually maintains a constant level during the muscle contraction. Despite such breakthroughs, however, it remains unclear exactly how this constant force is maintained in an otherwise chaotic system.

Bin Chen of the A*STAR Institute of High Performance Computing and Huajian Gao at Brown University, US, have now built a model to illustrate the process of skeletal and show how a constant force can be sustained by the protein motors.

The two key proteins in muscle contraction are actin and myosin. Myosin drives the system, forming a thick filament made up of numerous motors which ‘grab’ onto, bind to and slide past the thinner actin filaments during contraction. This ‘grabbing’ and sliding motion has been shown to be fairly chaotic in nature, with attachment and release happening at random. When the weight of an object exerts a load on the filaments — for example, when you try to lift something up — the muscles must contract, requiring the protein motors to generate a force opposite to the load.

Chen and Gao have created a new fiber model to demonstrate how contraction forces work. “Our model is designed for the sarcomere,” Chen explains. “We consider the thin filament as an elastic rod under a filament force, which is driven by multiple stochastic myosin motors that convert the chemical energy of adenosine-5'-triphosphate (ATP) hydrolysis into stored elastic energy and then function like swinging arms.”

The results show that the unique way in which the myosin motors randomly attach and release from actin, coupled with the elastic properties of the motors, generate a consistent force across the whole sarcomere. When there is a higher filament load, more myosin motors are attached to the actin, but the overall motor force remains constant.

“This regulation mechanism may exist in various biological processes and dramatically induces order within a chaotic system,” explains Chen. “Our modeling framework can also be further adapted to study the behaviors of other actomyosin complex structures, which is part of our plan for future work in this area.”

Explore further: Scientists throw light on the mechanism of plants' ticking clock

More information: Chen, B. et al. Motor force homeostasis in skeletal muscle contraction. Biophysical Journal 101, 396–403 (2011) doi:10.1016/j.bpj.2011.05.061

add to favorites email to friend print save as pdf

Related Stories

Scientists flex their muscles to solve an old problem

Apr 11, 2011

(PhysOrg.com) -- In a famous experiment first performed more than 220 years ago, Italian physician Luigi Galvani discovered that the muscles of a frog's leg twitch when an electric voltage is applied. An international ...

Muscle atrophy through thick but not thin

Jun 08, 2009

During desperate times, such as fasting, or muscle wasting that afflicts cancer or AIDS patients, the body cannibalizes itself, atrophying and breaking down skeletal muscle proteins to liberate amino acids. In a new study ...

Tidy motor protein folds away when the job is done

Oct 03, 2006

A discovery by University of Leeds researchers has revealed how a motor protein shuts itself down and becomes compact when it has no cargo to carry. It then goes in search of more cargo, perhaps carried by other passing proteins.

Recommended for you

Fighting bacteria—with viruses

Jul 24, 2014

Research published today in PLOS Pathogens reveals how viruses called bacteriophages destroy the bacterium Clostridium difficile (C. diff), which is becoming a serious problem in hospitals and healthcare institutes, due to its re ...

Atomic structure of key muscle component revealed

Jul 24, 2014

Actin is the most abundant protein in the body, and when you look more closely at its fundamental role in life, it's easy to see why. It is the basis of most movement in the body, and all cells and components ...

Brand new technology detects probiotic organisms in food

Jul 23, 2014

In the food industr, ity is very important to ensure the quality and safety of products consumed by the population to improve their properties and reduce foodborne illness. Therefore, a team of Mexican researchers ...

Protein evolution follows a modular principle

Jul 23, 2014

Proteins impart shape and stability to cells, drive metabolic processes and transmit signals. To perform these manifold tasks, they fold into complex three-dimensional shapes. Scientists at the Max Planck ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

HannesAlfven
1 / 5 (2) May 03, 2012
The body is not a mechanical system. It is fundamentally electromagnetic. Proteins are covered in alternating charges which are sized to the dimensions of the water molecule. That is no accident. The polywater debates have distracted people from the observational fact that water does indeed behave differently in the presence of proteins. The proteins can structure the water into a quantum coherent state. The cells are behaving as gels, which can transition between phases, based upon the very rapid electrochemical folding of proteins. Gels give us all of the components we need to create an efficient biological cell. Mechanical systems are not efficient, and nature opts for efficiency.
kaasinees
2.3 / 5 (3) May 03, 2012
Water is used by proteins to pump protons.

http://sciencedai...3643.htm