News Agency | ILLINOIS

CHAMPAIGN, Ill. – In a first demonstration of “electron videography,” researchers have captured a microscopic moving image of the delicate dance between proteins and lipids found in cell membranes. The technique can be used to study the dynamics of other biomolecules, loosening the limitations that have limited microscopy to still images of solid molecules, say researchers at the University of Illinois Urbana-Champaign and collaborators at the Georgia Institute of Technology.

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“We go beyond taking individual snapshots, which provide structure but not dynamics, and continuously capture the molecules in water, their original state,” says study leader Qian Chen, an Illinois professor of materials science and engineering. “We can really see how proteins change their configuration and, in this case, how the entire self-assembled structure of proteins and lipids fluctuates over time.”

The researchers reported their technique and findings in the journal Science Advances.

Electron microscopy techniques create images at the molecular or atomic scale, yielding detailed images at the nanometer scale. However, they often rely on samples that are frozen or fixed in place, leaving scientists to try to deduce how molecules move and interact – like trying to map out the choreography of a dance sequence from a single frame of film.

“This is the first time we’ve looked at a protein on an individual scale and haven’t frozen or tagged it,” said Georgia Tech professor Aditi Das, a corresponding author on the study. “We usually need to crystallize or freeze a protein, which poses challenges when capturing high-resolution images of flexible proteins. Alternatively, some techniques use a molecular tag that we track, rather than looking at the protein itself. In this study we see the protein as it is, how it behaves in a liquid environment and how lipids and proteins interact with each other.”

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The researchers achieved videography by combining a new water-based transmission electron microscopy method with detailed computational modeling at the atomic level. The water-based technique involves encapsulating nanometer-scale droplets in graphene so that they can withstand the vacuum in which the microscope operates. By comparing the resulting video data with molecular models, which show how things should move based on the laws of physics, the researchers can not only interpret but also validate their experimental data.

“Currently, this is really the only experimental way to film this kind of movement over time,” says John W. Smith, the paper’s first author, who completed the work while still a student in Illinois. “Life is fluid and it is in motion. We try to find out the finest details of that connection in an experimental way.”

For the new study – the first published demonstration of the electron videography technique – the researchers examined nanoscale disks of lipid membranes and how they interacted with proteins normally found on the surface of or embedded in cell membranes.

“Membrane proteins sit at the interface between cells and between the inside and outside of the cell and control what goes in and out,” Smith said. “They are predominantly targets for medicine; they are involved in all kinds of processes, such as how our muscles contract, how our brains work, immune recognition; and they hold cells and tissues together. And the whole complexity of how a membrane protein works comes not just from its own structure, but also from the way it experiences the lipids around it.”

Electron videography allowed the researchers to see not only how the entire lipid-protein assembly moved, but also the dynamics of each component. The researchers found that there were several regions within the nanodisk, and both more fluctuations and more stability than expected.

While it is often assumed that the influence of a membrane protein’s movement is limited to the lipid molecules immediately surrounding it, the researchers saw more dramatic fluctuations over a larger range, Smith said. The fluctuations took the shape of a finger, like slime splattering on a wall. But even after such a dramatic move, the nanodisk would return to its normal configuration.

“The fact that we saw those domains, and we saw them recover from those processes, suggests that interactions between the protein and the membrane actually have a broader reach than is often thought,” Smith said.

The researchers plan to use their electron videography technique to study other types of membrane proteins and other classes of molecules and nanomaterials.

“With this platform, we could study ion channels that open and close to regulate current and cell-to-cell interactions,” Chen said. “Adapting this platform for biological systems entails major risks and requires years of effort. We are extremely grateful for the support of the Air Force Office of Scientific Research Biophysics Program, which has been behind every advancement of the platform. It has been essential to our success.”

Qian Chen is also affiliated with the Department of Chemistry, the Beckman Institute for Advanced Science and Technology, the Carle Illinois College of Medicine, and the Materials Research Laboratory at Illinois.