Video reveals new elastic protein capable of stretching to 2.5 times its length

Scientists from the ICR and collaborators in Germany have used the latest imaging technologies to reveal a new component of muscle, an elastic protein, that is capable of stretching up to two-and-a-half times its own length using a never-before-seen property.

The team have published detailed images of the protein – called myomesin, which links muscle filaments - in the latest edition of the journal PLoS Biology, and have released an animated video showing the way the protein can stretch.

Muscles generate substantial mechanical forces as they contract and relax, so their molecular structures must be elastic and yet extraordinarily stable.

The team – led by scientists at the European Molecular Biology Laboratory (EMBL) in Hamburg and involving the Technical University of Munich - set out to investigate the structure of the protein in order to reveal the mechanism behinds its ability to stretch.

The research team used a range of new technologies to piece together the precise 3D structure of myomesin – including electron microscopy, protein crystallography, solution X-ray scattering and atomic force microscopy.

Their first step was to divide the myomesin molecule into smaller segments, which allowed a method called protein crystallography to be used to precisely determine the structure of each individual component.

The next step involved using an electron microscope, a scientific instrument that uses a beam of electrons to magnify an image into far more detail than is possible using a conventional microscope.

The ICR is home to a world-leading team which specialises in using electron microscopy to analyse protein molecules. Normally, the team uses these techniques to reveal the 3D structure of protein complexes that are involved in cancer development. Knowledge of protein structure is frequently a key factor in cancer drug discovery.

In this project, Dr Edward Morris and colleagues used electron microscopy, which along with solution X-ray scattering experiments conducted by their collaborators, was used to work out how the segments of myomesin fit together.

Finally, the research team used atomic force microscopy to measure the elasticity of the molecule. By combining these technologies, they revealed that the protein was able to unfold in a way that was previously unknown. The stretchy part of myomesin is like a string of pearls, with immunoglobulin (Ig) domains spaced by links known as α-helices. When the protein is pulled, the α-helices unfold, whereas the Ig domains do not – a finding that could help to solve an ongoing debate in the field about the potential elasticity of proteins formed from multiple Ig domains.

Dr Morris, a co-author and Team Leader at the ICR, said: “Myomesin is remarkable in its ability to extend to nearly two-and-a-half-times its original length. Our study explains how myomesin can be both elastic and yet maintain the overall stable structures required in muscle. It’s likely that the new mechanism we discovered is found in many other elastic proteins, so our findings have shed light on what until now has been a mystery of the human body.

"The study may ultimately also have implications for our understanding of the way cancer develops. Changes to the elasticity of cells and tissues are observed in cancer patients, and we know that elasticity is extremely important in the process of metastasis, which is the spread of cancer around the body from its original location. The more we can understand about this process, the better chance we have to stop it occurring."

Superhelical Architecture of the Myosin Filament-Linking Protein Myomesin with Unusual Elastic Properties published in PloS Biology on February 14, 2012