Exploring retromer complex interactions

Updated: Aug 25

Q&A with Refeyn Travel Grant winner Kevin Chen

Kevin sitting at a desk, looking at the camera. On the desk there is a stack of printed scientific papers and a laptop. The screen of the laptop shows a digital model of a protein. Behind him there is a shelf full of books.

Dr. Kai-En “Kevin” Chen is one of the winners of this year’s Refeyn Travel Grants. Our travel grants, which are open to all mass photometry users, provide up to £2000 in travel expenses for the recipient(s) to attend a scientific conference of their choice.

Kevin is a postdoctoral researcher in Prof. Bret Collins’s Molecular Trafficking lab, Institute for Molecular Bioscience (IMB), University of Queensland (Brisbane, Australia).

In this Q&A, Kevin chats with Refeyn’s Nico Palanca about the research he will present at his chosen conference and the role of mass photometry in his project. If you find his work interesting and would like to hear about it in more detail, do not miss his upcoming webinar!


Hi Kevin, thanks a lot for giving us a bit of your time! To start, could you please tell us about your line of research?

My project is related to the interactions between the retromer protein complex and other components of the endosomal system such as cargo adaptors or accessory proteins. When a transmembrane receptor binds to its ligand, it is internalized along with it inside a vesicle. These receptors are then transported back to the plasma membrane to be reused. The retromer protein complex plays an important role in in this process of sorting and recycling transmembrane receptors.

Initially, my project was mostly structural research that aimed to determine how retromer interactions happen at the molecular level. However, we had a side project with Dr. Toby Passioura at the University of Sydney involving Random non-standard Peptide Integrated Discovery (RaPID) screening. RaPID screens large libraries of rigid, stable macrocyclic peptides to look for those able to interact with a target molecule.

We sent retromer samples to Toby to screen with RaPID, and we found some peptides that interacted with the complex. This was interesting because the dysfunction of the retromer complex is associated with neurodegenerative diseases, which makes it a relevant therapeutic target. Since then, what was initially a side project has become an important focus of my work.

How did you learn about mass photometry, and what role does it play in your project?

When the IMB got the mass photometer, one of the students in our lab was very excited to give it a try. We were working on characterizing the peptides we discovered with RaPID and used mass photometry to check if the complex maintained its oligomeric state after the peptides were added.

This check was our first experiment with mass photometry, and ever since then it has become very important for our project. We study many protein interactions, so the low sample and time requirements of mass photometry make it valuable to us. We use it mainly to determine the stoichiometry of protein complexes and to check if they are adequately formed before doing structural analysis. It turned out to be a very good machine!

Which conference are you planning to attend with the travel grant, and why did you choose it?

I am going to the ComBio2022, which is taking place at the end of September in Melbourne. It’s a major conference in Australia. I feel excited about it because I’m going to give a talk in the drug discovery section and my work on the retromer complex has made me interested in the translational side of research. This conference will offer great networking opportunities and, as my project is moving towards drug discovery, I hope to get useful feedback for my current research from experts in the field.

What are you going to present at the conference?

My talk is going to be about using the RaPID approach for the study of the retromer complex, both for drug discovery and as a molecular tool for functional studies. As I mentioned before, we did find some macrocyclic peptides that bind to the retromer complex.

In contrast with other drug discovery studies, we were looking for stabilizers for the complex rather than inhibitors, as we are interested in recovering retromer function when it is impaired. We discovered a stabilizing peptide that is a good candidate for drug development, and we are still working on solving its exact structure and interactions with the retromer complex.

But what is also interesting is that we found some inhibitor peptides, all of which interacted with the same part of the retromer complex and shared a binding motif. This made us wonder whether endogenous ligands of the retromer complex also share a similar, evolutionarily conserved binding mechanism. In this case, RaPID gave us a lead for another future line of inquiry, showing that it can be very useful beyond drug discovery.

The next step for my research will be to keep working with the retromer-stabilizing cyclic peptide we discovered. We only know roughly where it binds to the complex, and I am interested in getting a better, atomic resolution of the interaction site. Once we know that, we can take steps towards optimizing the peptide for therapeutic purposes or using it as a base to design a small molecule that behaves similarly.


We want to thank Kevin again for telling us about his work! Remember to check out his webinar if you want to know more about this topic. If you want to learn about mass photometry, you can find more information in this application note. And if you are interested in using mass photometry for assessing protein oligomerization and stoichiometry, check out a good case study in this webinar about quantitation of the calmodulin-dependent protein kinase II (CAMKII).


Further resources:

Application note – Basics of mass photometry

Here you can learn about the basics of mass photometry and the main advantages it offers for the analysis of biomolecules.

Webinar – Using Mass Photometry to Quantitate CaMKII stoichiometries

In this webinar, Dr. Margaret Stratton (UMass Amherst) talks about her work on the role of CaMKII in different tissues. Mass photometry has been used to quantitatively determine the stoichiometry of different variants of this crucial oligomeric enzyme.

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