Studying intermolecular protein associations with FIDA - a conversation with Prof. Daniel Otzen

FIDA in the Study of Protein Interactions and Enzymes: A Conversation with Prof. Daniel Otzen

Professor Daniel Otzen from iNANO at Aarhus University leads a lab that works across two distinct areas of protein research: understanding harmful protein aggregation in diseases like Parkinson’s, and developing enzymes that perform useful functions, such as working at low temperatures or breaking down plastic. Despite the differences between these topics, one instrument has become central to both: FIDA.

We spoke with Professor Otzen about how FIDA supports his research, especially in addressing complex questions around protein oligomers, membrane binding, and enzyme behavior. You can also watch the full interview here.

Addressing Oligomer Interactions Under Native Conditions

In studying Parkinson’s disease, one of the key questions in Prof.Otzen’s lab is understanding what makes certain protein aggregates harmful. While large insoluble aggregates may simply accumulate in cells, smaller soluble oligomers are more mobile, and potentially more harmful.

“Aggregates can be insoluble when they accumulate in the cell, and then they're just large and lie around and don't do much. But they can also be small soluble complexes that we call oligomers. They can move around quite quickly and interact with a lot of things.”

These experiments are technically challenging, especially because oligomers are hard to produce in large amounts and are sensitive to experimental conditions.

“The oligomers can be made in the lab, but you can't make a lot of them. So you need to have a technique that can work with small concentrations and small volumes, and the FIDA is second to none there.”

He also emphasized that FIDA allows measurements in solution, without the need for immobilization.

“You also want to work with it under conditions where you don't manipulate these oligomers, you don't bind them to a surface or immobilize them... FIDA is really great here because it allows you to have it in solution and then expose it to other components. (...) It has to be under truly equilibrium conditions and all this is something that FIDA provides.”

Distinguishing Binding from Functional Effects

Prof. Otzen explained that FIDA has been “a game changer” in his field, especially for understanding how oligomers bind to membranes or other components.

''It allows you to measure, correct or robust equilibrium affinity constants for how oligomers can bind to whatever you expose it to.''

He described how FIDA helps distinguish the act of binding from downstream functional effects, such as membrane leakage:

“We know that they can bind to membranes and lead to disruption of them, so that things can leak out. But there is a difference between binding and leakage. And by having the FIDA technique, you can actually directly measure if the oligomer is binding to the membrane or not. That is really useful.”

Understanding Enzyme Assembly and Activity

Prof. Otzen also uses FIDA to study enzymes, which can exist as different oligomeric states (monomers, dimers, tetramers) each with potentially different activity.

“FIDA is really great because, of course, it provides information about the size, and you can really go down in extremely low concentrations to find out how their concentration affects the association of the protein.”

This size information helps the lab model how enzyme behavior changes with concentration, and ultimately how this affects catalytic function.

Specificity in Complex Mixtures

Another major strength Prof.Otzen highlighted is FIDA’s ability to detect interactions in complex biological samples, such as cell lysates:

“You just need to have a fluorescently labeled protein of interest... and then you can expose it to a very complex mixture and see whether it binds to something in that mixture (...) That mixture will be invisible in FIDA because the components are not fluorescently labeled. (...) We've actually done that to show, for example, how the oligomer can bind to different components in a cell lysate, where there can be thousands of different components.”

While FIDA doesn’t identify the binding partner directly, Prof.Otzen noted that this kind of data helps guide further experiments.

“It simply provides readouts under realistic physiological conditions, I'd say.”

Efficient Screening of Biologics

FIDA has also been valuable in larger-scale antibody screening. Prof. Otzen described a recent study where the lab tested interactions between more than 30 monoclonal antibodies and protein oligomers.

“We looked at more than 30 different monoclonal antibodies and how they interact with the oligomer. And we could measure all of their interactions... at no particular cost of either antibodies or oligomer, simply because FIDA is such an economical technique. (...) We can also compare them rigorously with each other under exactly the same conditions. (...) That has also really made a difference for us in our understanding and our ranking of these different antibodies.”

Otzen sees a strong potential for broader adoption of FIDA:

“I believe that FIDA could really become a basically standard technique within the pharmaceutical industry to assay interactions between biologics and their targets.”

What Makes FIDA Unique in Prof. Otzen's Lab?

When asked what he would miss most if FIDA disappeared from the lab, Otzen highlighted the clarity and interpretability of the readout:

“What I really like about FIDA is that you get a very understandable readout. You get the hydrodynamic radius. Many techniques only provide an indirect readout, so FIDA's very straightforward and I think understandable and also testable outcome.”

He also noted the combination of strengths: working under equilibrium conditions, handling low sample volumes, and supporting higher throughput.

“The fact that it's under equilibrium conditions at little cost, and you've got high throughput, or at least medium throughput options... they all help out (...)The fact that you get a truly molecular picture of what's going on is unique for FIDA.”

Looking Ahead: Plastics and Kinetics

One of the next frontiers in Prof. Otzen’s lab is plastic-degrading enzymes. He’s interested in using FIDA to study how enzymes interact with microplastic fragments, by first breaking plastics down to small, suspendable particles and monitoring them as they degrade.

“I'm really keen to see how we can monitor the depolymerization or the sort of increased size reduction of these small plastic pieces by FIDA in a very direct fashion.”

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Professor Otzen’s interview paints a clear picture of how FIDA is used to answer diverse scientific questions across protein aggregation, enzyme function, molecular interactions, and therapeutic screening. The ability to work in solution, under equilibrium, and at low concentrations—while delivering direct, size-based readouts continues to make FIDA a critical tool in his lab.

We highly recommend that you visit our literature base, where you can find publications from prof.Otzen (and our other users') laboratory. Access the literature here.