Movement in the smallest of spaces: researching polymers through neutron spin

Proteins are long-chain molecules essential for all biochemical processes in our body. How they move exactly in the densely packed cell interior has yet to be clarified. A Spanish research team has investigated at the MLZ how the dynamics of mimetic model polymer nanoparticles change depending on their environment.

Dr. Stefano Pasini from Forschungszentrum Jülich and his colleagues from Donostia-San Sebastián were able to determine the dynamics of long-chain polymers in dense packing using the J-NSE ‘PHOENIX’ instrument. © Wenzel Schürmann / TUM

Dr. Stefano Pasini from Forschungszentrum Jülich and his colleagues from Donostia-San Sebastián were able to determine the dynamics of long-chain polymers in dense packing using the J-NSE ‘PHOENIX’ instrument. © Wenzel Schürmann / TUM

Imagine standing in a crowded place and trying to navigate the crowd. The proteins in our cells are constantly faced with this problem. They move around inside the cell, densely packed with other cell components, and must find the right partners for biochemical processes.

A model system of proteins
The so-called single-chain nanoparticles (SCNPs) are similar in size and structure to intrinsically disordered proteins and served the researchers at the Materials Physics Centre (MPC) in Donostia – San Sebastián, Spain, as a model system for this study.

Neutron spin as an indicator
To model the impact of macromolecular crowding, e.g. of the cell interior, the researchers observed the dynamics of the SCNPs in a dense solution of molecules of different sizes. They used neutron spin echo spectroscopy (NSE) with the newly upgraded J-NSE “PHOENIX” instrument at the MLZ. NSE makes it possible to determine the change in momentum that neutrons experience during a scattering process on the sample using the neutron spin, a fundamental property of elementary particles.

New superconducting magnetic coils
The measurements carried out for this work were among the first to be performed on the J-NSE instrument with the new superconducting magnetic coils and showed a significant improvement in resolution.

Free movement in dense crowds
“Thanks to the information provided by NSE, the researchers discovered that although the drift speed of SCNPs slows down in densely packed environments, their internal flexibility remains surprisingly unaffected,” says Dr. Stefano Pasini from the Jülich Centre for Neutron Science (JCNS) at the Heinz Maier-Leibnitz Zentrum (MLZ) who had conducted the measurements. “This means that these particles can still twist and turn in confined environments even under crowding.”

An important finding was that the size of the surrounding molecules has no significant influence on the internal movements of the SCNPs. Understanding these dynamics helps us to understand cellular processes such as protein folding and molecule recognition, which are essential for the smooth functioning of the cell.