Stretching helices help keep muscles together

Muscle protein stretches in novel way

Myomesin stretching to 2.5 times its length. Credit: EMBL/Wilmanns.

In this video, a protein called myomesin does its impression of Mr. Fantastic, the leader of the Fantastic Four of comic book fame, who performed incredible feats by stretching his body. Scientists at the European Molecular Biology Laboratory (EMBL) in Hamburg, Germany, have discovered that the elastic part of this protein can stretch to two and a half times its original length, unfolding in a way that was hitherto unknown.

In muscle, the stretchy tails of two myomesin molecules come together, forming an elastic bridge that keeps a bundle of muscle fibres together. Each tail looks like a set of pearls – called immunoglobulin-like domains (pink, blue) – spaced out along an elastic band of structures known as alpha helices (green). When the protein is pulled, as it is when muscles contract and extend, the helices unfold.

To obtain this unprecedentedly detailed view of myomesin’s three-dimensional structure and discover the secret behind its stretchiness, the scientists combined an array of techniques: X-ray crystallography, small angle X-ray scattering, electron microscopy and atomic force microscopy.

“Next, we would like to determine the structure of the complete myomesin filament,” says Matthias Wilmanns, Head of EMBL Hamburg, who led the work, “and to find out about the protein’s function in living organisms, starting with animal models.”

The work, published today in PLoS Biology, was conducted in collaboration with scientists from the Technical University of Munich, in Germany, and The Institute of Cancer Research, in the UK.

The video is also available on the EMBL YouTube Channel.

For more information on myomesin and muscle elasticity:
PLoS primer – “Making Muscle Elastic: The Structural Basis of Myomesin Stretching”