EPR at BPS2023 – A (Magnetic) Field of Opportunity

Austin Gamble Jarvi
Applications Scientist

One of the most personally striking moments at this year’s Biophysical Society Meeting came early in the conference – the first day. I sat in the CryoEM Symposium, where several hundred people were arrayed about the room, leaving few seats empty. The current speaker had asked how many of us among the audience had prepared a CryoEM grid before – and the vast majority of hands in the room went up. It was clear how widespread and ubiquitous the technique has become in recent years, spurred forth by the ‘resolution revolution.’ As an EPR spectroscopist, this is my hope for the future of my field: to cement EPR in the common vernacular of biophysical techniques to the point where every conversation doesn’t need to start with, “Are you familiar with EPR?”

Despite being still an incredibly niche technique, the current state of EPR is something to be excited about. EPR – electron paramagnetic resonance – is a diverse and robust technique that can unlock biophysical information by measuring nanoscale intramolecular distances, determining localized dynamics, and probing paramagnetic binding environments. Every year talented investigators are using this spectroscopy to discover new information and solve old problems. I had the chance to interact with several such groups and see firsthand the new directions the field is heading.

Prof. Indra Sahu (Campbellsville University) applied EPR distance methodologies to the KCNE3 membrane protein within a lipid bilayer. These distance measurements were used in conjunction with an existing NMR solution structure of this system, to provide a better understanding of the protein’s structure in its native physiological environment. These results were complemented by a series of dynamical measurements by CW-EPR (continuous wave EPR) used to further characterize the topology of the protein.

Additionally, Prof. Candice Klug’s group (Wisconsin Medical School) presented a study of CW-EPR dynamics measurements in the activation loop of a transmembrane kinase, IreK. This protein is involved in certain drug resistances in many bacteria, and the activation loop studied here is thought to be involved in regulating IreK’s activity. Such flexible and dynamic structures are difficult to resolve through crystallization, NMR, or CryoEM. Understanding the dynamics of this loop via EPR furthers our understanding of antibiotic resistance mechanisms, a critical consideration in modern pharmacology.

I was also impressed with a bevy of EPR distance constraints used to characterize membrane transport protein ApcT, presented by Prof. Kelli Kazmier (Hillsdale College). These measurements demonstrated pH-dependent conformational shifts, as well as provided insights into the conformations themselves. As membrane proteins are an incredibly important class of biomolecules, responsible for intercellular communication and messaging, ion transport, and are a huge target for drug development, these bodies of work present an excellent example of the power of modern EPR.

Beyond just exciting developments in EPR, this year’s BPS meeting was full of interesting science and rife with opportunities for EPR to step up. Amid many hot topics, intrinsically disordered proteins (IDPs) are a promising category of biomolecules that could benefit from the magnetic touch of EPR. Prof. Jane Dyson (Scripps) and Prof. Elizabeth Komives (UCSD) spoke at length on the relationship between such disorder and its function – specifically on a tumor suppressor and transcription regulator protein, respectively. The characteristic dynamism and flexibility of such biomolecules make them difficult to resolve through traditional means, and therefore they make an enticing target for further complementary EPR study.

In another session, Prof. Ryan Hibbs (UT Southwestern/UCSD) presented on gating mechanisms of an acetylcholine receptor derived from a torpedo ray. Amidst some impressive CryoEM structures, he noted a major bottleneck in this work is that structures have been solved only for the protein’s resting and desensitized state and that the active state structure is unknown. This problem derives from the short lifespan of the activated state of the protein, and the difficulty of catching such a dynamic snapshot by crystallization, CryoEM, or NMR. EPR’s ability to distinguish conformations within an ensemble of states – coupled with careful sample preparation, flash-freezing, and structural modeling – could be used to access structural information on such difficult problems.

BPS2023 was a great way to kick off the conference circuit at High Q this year. There was some excellent work in the field of EPR, but perhaps more importantly, there was a world of problems and applications we believe we can help solve. In thinking back to that first CryoEM session, such a moment may seem mundane in the current scientific landscape but even just a few years ago the answer to ‘who has prepared a CryoEM grid?’ may have been staggeringly different. I can see the opportunity for EPR to make its mark, where the question ‘who has prepared a sample for EPR’ may be met with similar results.

We have an exciting year ahead, and many more great conversations to have to with the scientific community. Our next stop – the Royal Society of Chemistry ESR Meeting. See you in Leeds!