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New avenues for research in membrane biology reveals the mobility of protein at work

Curator and Reporter: Dr. Premalata Pati, Ph.D., Postdoc

Membrane proteins (MPs) are proteins that exist in the plasma membrane and conduct a variety of biological functions such as ion transport, substrate transport, and signal transduction. MPs undergo function-related conformational changes on time intervals spanning from nanoseconds to seconds. Many MP structures have been solved thanks to recent developments in structural biology, particularly in single-particle cryo-Electron Microscopy (cryo-EM). Obtaining time-resolved dynamic information on MPs in their membrane surroundings, on the other hand, remains a significant difficulty.

Weill Cornell Medicine (WCM) researchers have found that they can record high-speed protein movements while linking them to function. The accomplishment should allow scientists to examine proteins in more depth than ever before, and in theory, it should allow for the development of drugs that work better by hitting their protein targets much more effectively.

The researchers utilized High-Speed Atomic Force Microscopy (HS-AFM) to record the rapid motions of a channel protein and published in a report in Nature Communications on July 16. Such proteins generally create channel or tube-like structures in cell membranes, which open to allow molecules to flow under particular conditions. The researchers were able to record the channel protein’s rapid openings and closings with the same temporal resolution as single channel recordings, a typical technique for recording the intermittent passage of charged molecules through the channel.

Senior author Simon Scheuring, professor of physiology and biophysics in anesthesiology at WCM, said,

There has been a significant need for a tool like this that achieves such a high bandwidth that it can ‘see’ the structural variations of molecules as they work.

Researchers can now produce incredibly detailed photographs of molecules using techniques like X-ray crystallography and electron microscopy, showing their structures down to the atomic scale. The average or dominant structural positionings, or conformations, of the molecules, are depicted in these “images,” which are often calculated from thousands of individual photos. In that way, they’re similar to the long-exposure still photos from the dawn of photography.

Many molecules, on the other hand, are flexible and always-moving machinery rather than fixed structures. Scientists need to generate videos, not still photos, to reveal how such molecules move as they work, to see how their motion translates to function to catch their critical functional conformations, which may only exist for a brief moment. Current techniques for dynamic structural imaging, on the other hand, have several drawbacks, one of which being the requirement for fluorescent tags to be inserted on the molecules being photographed in many cases.

Scheuring and his lab were early adopters of the tag-free HS-AFM approach for studying molecular dynamics. The technology, which can photograph molecules in a liquid solution similar to a genuine cellular environment, employs an extremely sensitive probe, similar to a record player’s stylus, to feel its way over a molecule and therefore build up a picture of its structure. Standard HS-AFM isn’t quick enough to capture the high-speed dynamics of many proteins, but Scheuring and colleagues have developed a modified version, HS-AFM height spectroscopy (HS-AFM-HS), that works much faster by collecting dynamic changes in only one dimension: height.

The researchers used HS-AFM-HS to record the opening and closing of a relatively simple channel protein, OmpG, found in bacteria and widely studied as a model channel protein in the new study, led by the first author Raghavendar Reddy Sanganna Gari, a postdoctoral research associate in Scheuring’s laboratory. They were able to monitor OmpG gating at an effective rate of roughly 20,000 data points per second, seeing how it transitioned from open to closed states or vice versa as the acidity of the surrounding fluid varied.

More significantly, they were able to correlate structural dynamics with functional dynamics in a membrane protein of this size for the first time in a partnership with Crina Nimigean, professor of physiology and biophysics in anesthesiology, and her group at WCM.

The demonstration opens the door for a wider application of this method in basic biology and drug development.

Sanganna Gari stated,

We’re now in an exciting period of HS-AFM technology, for example using this technique to study how some drugs modulate the structural dynamics of the channel proteins they target.

Main Source

Technique reveals proteins moving as they work. By Jim Schnabel in Cornell Chronicle, August 16, 2021.

https://news.cornell.edu/stories/2021/08/technique-reveals-proteins-moving-they-work

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