Capturing protein motion at FemtoMAX

Greger Hammarin talks about using electric fields to induce protein motion and capturing it with the short X-ray pulses at FemtoMAX.

Your body contains a large variety of different proteins. They are big, complex molecules with diverse functions, from transporting oxygen in your blood to making your muscles contract. Many proteins change their shape and move as they perform their task. A research team from the University of Gothenburg recently visited the beamline FemtoMAX to develop a method for studying moving proteins. They use electric fields to stimulate motion of the proteins in a sample while imaging them with the X-ray beam.

To study how proteins move, we need something to nudge them and then image them after they have changed position. Certain proteins are activated by light and in that case, the researchers can hit them with a laser pulse to provoke the motion. However, that is far from always the case. In the method being developed by the Gothenburg team, the proteins are instead subjected to an electric field that make them move.

The field is synchronized to the short, femtosecond scale (10-15 s) X-ray pulses delivered at beamline FemtoMAX. Each X-ray pulse hitting the sample is like taking a photograph using extremely short shutter speed, just like trying to get sharp images of players on a football field. The X-ray pulses at FemtoMAX are short enough to let the researchers capture the instantaneous position of the protein. By varying the time between the electric field and the X-ray pulse they can see different stages of the movement and even put the frames together as a movie of the protein motion.

The research team used the method to study tubulin, a protein which is the building block of tiny strings called microtubules inside the cells. Microtubules have important functions pulling the cells apart in cell division as well as holding the cell up as a type of skeleton or working as transport lines for substances within the cell.

Microtubules are very dynamic in the cell, they grow and shrink and reorganize all the time. We have seen with other methods that electric fields will affect the equilibrium and speed of this dynamics, says Greger Hammarin, one of the researchers in the Gothenburg team.

It was the first visit by the researchers at the FemtoMAX beamline, and the plan is to come back with more samples of tubulin and other moving proteins.

It’s the connection between structure and function that interests us. We have applied for more beamtime this autumn and hope to get the opportunity to do further studies after this proof-of-concept experiment now that we know it can be done at FemtoMAX, Hammarin concludes.