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June 02, 2020

The discovery of protein A

By Conor McKechnie and Dodi Axelson

The discovery of protein A

Is it possible to love one protein? Dodi and Conor learn that it is, in the special case of a protein that’s integral in purifying many of today’s biologic drugs.


DODI: Conor, you're a big fan of bacteria. Should we talk about the one that most people know and do not love?

CONOR: Staphylococcus? The famous cause of Staph infections?

DODI: Yes. Why not? Yeah, these bacteria are not to be messed with. But some good things have come from understanding them. Such as, drumroll please...

CONOR: Oh, how exciting.

DODI: The discovery of protein A.

CONOR: Protein A. Finally, an episode on protein A. Discovered in our lifetime and is going to drive just the most incredible things for generations to come. So, is that what matters in today's episode?

DODI: In fact, it is. Let's find out about protein A.

CONOR: Okay, so what do I need to know about protein A?

DODI: Well, we do like a history lesson here on Discovery Matters. So, put the jukebox on, slick back your hair, and imagine that we are back in 1958. We're at the Institute of General Pathology at the University of Copenhagen. And Professor Klaus Jensen is exploring cell walls.

GLEN BOLTON: Jensen’s lab first observed the binding of protein A to serum antibodies. And it's interesting, they speculated the body has natural antibodies against Staphylococci. They demonstrated that 100% of healthy subjects had binding to this antigen A. And they speculated that it was due to passive transmission of antibodies from the mother to children.

CONOR: Okay, there was a whole load of information there.

DODI: Yeah, we are going to break this down together.

CONOR: As we would expect. So, who are we talking to?

GLEN: My name is Glen Bolton. I work at Amgen. I'm located in Cambridge, Massachusetts. I've been in purification development for about 20 years.

CONOR: Okay, so Glen basically said that Klaus Jensen discovers something, but he's not exactly sure about what he's actually discovered.

DODI: That's right. It's just the kind of story we love to retell here on Discovery Matters.

CONOR: Yeah, it sounds very familiar, doesn't it? And Jensen, it sounds very Scandinavian. Is everything that we do coming back to Scandinavia?

DODI: Scandinavians, in fact, do play a big part in this story like many others. A few years later, in 1962, another set of Scandinavian researchers Löfkvist and Sjöquist in Bergen, Norway kind of finish off what Jensen had started. And they confirmed that antigen A was in fact a surface protein on the bacterial wall of certain strains of Staphylococcus aureus bacteria.

JOSEFIN BOLIK: Then two years later, they named it protein A after aureus.

CONOR: I recognize that voice. Let's meet her.

JOSEFIN: My name is Josefin Bolik. And I work as a global product manager at Cytiva. I'm responsible for the next-generation protein A chromatography resins.

DODI: It wasn't until 1978 when somebody decided this could make a good purification product.

JOSEFIN: That's where it all started for how we utilize protein A today.

DODI: So, let's break down everything to do with protein A.

CONOR: Please, let's do.

JONATHAN ROYCE: Protein A's function for Staph aureus is actually to interrupt your immune system.

CONOR: Now that voice sounds familiar as well.

DODI: Yep, that is our former colleague, Jonathan Royce. He loves protein A. I mean, loves it.

JONATHAN: Protein A sits on the surface of these bacteria. And when your body produces antibodies to try to kill the bacteria, protein A binds those antibodies, and flips them upside down, so the important part of your immune response can't reach the wall of the bacteria. I think it's really interesting, because it is one of these maybe not accidental discoveries, but it's something that we have discovered in nature and then found a way to apply in a very industrial setting. And I think it's also really interesting that in the beginning, no one thought this technology would ever be used at the industrial scale. I mean, it was a lab-scale product at the beginning. If you read some of the first product managers' notes, which were on typed paper, they were forecasting that maybe someday we'll sell a liter of protein A. Today, Cytiva and other companies produce tens of thousands of liters of this product. It's a fascinating story from both of those angles, I think.

JOSEFIN: It is a very interesting molecule. As Jonathan said, it has three alpha helixes. With that structure the amino acids are pretty much protected. When you treat with, for example, alkaline solutions, it can actually protect the amino acids a little bit as compared to other protein scaffolds, which perhaps have more beta sheets, like protein G. Those amino acids are more exposed to treatments. So, protein A is a very interesting molecule because it has a good structure that you can engineer to bind to other proteins as well.

JONATHAN: It's also beautiful. It's quite a striking structure when you see these three triple helixes and the way that they're intertwined with one another. It's unique in the way it looks. And it looks really nice when you see the 3D structure in a color image. That's also a reason to love protein A.

CONOR: So, it's like the kind of natural antidote in our immune system.

DODI: Exactly.

CONOR: Okay, so this is a lot of information. Is it then like flipping a pancake and not cooking the other side? It's the casing on a Kinder Egg? I'm looking for a metaphor here, help me out.

GLEN: If you put all your clothes in the washing machine, with a lot of synthetic material and one piece of wool, and you want to grab just that piece of wool, you could put the rough side of a piece of Velcro™ in as well. And the Velcro would only stick to the wool. And that's how protein A works. It only grabs that thing that you want, and it doesn't grab anything else.

DODI: So, that's protein A. It only grabs the thing you want and leaves everything else alone.

CONOR: Let's backtrack and tell people listening a little bit more about monoclonal antibodies, or mAbs, because that's what we call them in our industry. They're proteins, antibodies made by identical cloned immune cells, which is why they're called monoclonal. These identical clones bind to specific proteins on cells that are involved in disease pathways like cancer and immune diseases. mAbs have really heralded a complete revolution in treatments for all sorts of diseases from cancer to rheumatoid arthritis and so on. Many of today's top selling drugs are mAbs. And protein A, it turns out, is just incredibly important in the manufacturing of these drugs on an industrial scale.

JOSEFIN: Yeah, so, this natural specificity to IgGs, immunoglobulins, is very good because you can get rid of all the animal-derived nutrients in your cell feed, basically. Protein A only binds your targets, your drug in this case, which is your monoclonal antibody. You get rid of everything else, and that has the benefit that you can reduce the number of subsequent steps. So, protein A has a very good advantage because it's very specific, and you get very high purity at the end.

There is a particular constant part that protein A wants to bind to. If you have that on a chromatography resin, for instance, then you bind your drug to the protein A on the resin. Everything else from your cell culture feed—all the proteins, nutrients, everything—flows through, and you get rid of that, which gives very high purity of your drug.

CONOR: What's the future, then? How can something this efficient get any better, or is there a risk of disruption by another technology or another protein?

JOSEFIN: Protein A has been engineered since that first resin came out. We've made it more alkaline stable. With all of those nutrients in the mAb feeds, the protein A purification step is prone to bioburden incidents. Cleaning the resin more harshly can get rid of that problem. So, we have engineered protein A over the years to allow cleaning resins with a higher concentration of sodium hydroxide. Going beyond just utilizing protein A on chromatography beads, it can be attached easily to other new technologies based on membranes or fibers. I think that's what we're going to see going forward.

DODI: So, here's what that means for drug making.

JOSEFIN: With newer technologies you still have that protein A specificity and can reduce complications from bioburden incidents. You can actually improve the productivity of your process even more, you can run even faster. Over the years there has been a lot of focus on making the beads to have better pressure-flow properties, and so on, to run the processes faster and respond to the increased mAb concentrations (titers). Now, customers want to have even more productivity. And that's where we're going to see those new technologies come in place. I think protein A is going to be very useful in those new technologies.

DODI: Protein A columns are the weakest link in downstream purification with respect to the bioburden risk. Josefin is going to explain that.

JOSEFIN: All sorts of bacteria can get into your process and grow to larger numbers in the nutrients used to grow the cells making the mAbs. So that is what we mean with a bioburden incident. And this is very critical to companies. They have to be in control over this and be able to show that they can actually reduce bioburden risk in a very efficient way.

CONOR: So, when Josefin's talking about increasing speed, what are we talking about exactly? Are we talking about like from hours to minutes or months to hours? How much speed?

JOSEFIN: We typically call it grams per hours in terms of productivity, or grams per liter per hour if it's a resin. So, increasing or improving speed means that you can produce more grams per hour, basically.

CONOR: Okay, so we mentioned cancer. When we see how much cell and gene therapy is evolving in the race to cure cancer, how then do monoclonal antibodies compete with them?

JOSEFIN: Well, I think both technologies are here to stay. Data was presented by two companies in late 2019 showing that bispecific antibodies are actually outperforming CAR T treatments. That is a very interesting thing going forward to look out for. So, I think antibodies definitely can still have their space when it comes to cancer treatment.

DODI: For Glen, he says that if you imagined protein A as a car, it's like your old faithful. It's the car that you drive every day, not the Sunday convertible.

GLEN: Yeah, I think that's a good analogy. You want reliable, economical transportation, that you don't have to worry about getting to point A to point B. And then it's sort of a reliable economic transportation for us to get early-stage drugs to the clinic and to commercialization for patients.

DODI: And he carries on saying that it really is a lifesaver.

GLEN: It's something that I value a lot because we have to get these drugs out fast, we have to meet the clinical timelines, we have to get them to patients quickly. I don't have a lot of time to spend developing the conditions I want to get the material through with very little risk. I don't want to lose yield. I don't want to give something that's too impure. So, to me protein A is kind of a lifesaver in that I can very quickly produce these drugs and move them along to the patients with low development effort. And with good confidence, I'm going to get high yield and high purity. For me, that's key. I don't have to worry about whether it's going to work. Am I going to lose all my product? Is my product going to be too impure when we're doing early stages of development and we want to rapidly get material out?

CONOR: So, from something scary and unknown and unexpected, we've found something that's provided enormous benefit to the biotech industry and to patients all around the world.

DODI: Exactly. And it's another discovery in an unexpected place. And it's another story for you to use, Conor, when you talk about your love of bacteria.

CONOR: I love those little guys. Yeah, and my love for ratings for our podcast. So please do that. And thank you for listening.

DODI: Catch us anywhere you listen to podcasts--on Spotify, Apple podcasts. Stitcher, and Himalaya, where our listeners in Asia can find us.

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