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First discovered in 2001, the protein PINK1 has been directly linked to Parkinson’s disease. However, until now, scientists had been unable to visualize human PINK1 or understand how it is switched on or attaches to the surface of damaged mitochondria as part of mitochondrial quality control.
In a world-first, researchers from the Walter and Eliza Hall Institute of Medical Research (WEHI) have determined the structure of human PINK1 bound to mitochondria. The findings, published in the journal Science, reveal new ways to “switch on” PINK1 and could pave the way for new drugs to treat Parkinson's disease.
In healthy individuals, PINK1 gathers on mitochondrial membranes and signals when broken mitochondria need to be removed (a process known as mitophagy). The signal is unique to damaged mitochondria and when PINK1 is mutated, the mitophagy process no longer functions correctly and toxins accumulate in the cell, causing cell death.
Brain cells, which require a lot of energy produced by mitochondria – also known as the powerhouse of the cell – are especially sensitive to this damage.
Technology Networks spoke with Dr. Sylvie Callegari, senior research officer at WEHI, to learn more about how the researchers were able to solve this decades-long mystery and what it could mean for future drug discovery efforts.
Blake Forman (BF):
Senior Science Writer
Technology Networks
Blake pens and edits breaking news, articles and features on a broad range of scientific topics with a focus on drug discovery and biopharma. He earned an honors degree in chemistry from the University of Surrey. Blake also holds an MSc in chemistry from the University of Southampton. His research project focused on the synthesis of novel fluorescent dyes often used as chemical/bio-sensors and as photosensitizers in photodynamic therapy.
Can you walk us through the breakthrough discovery your team made and how it helps us understand Parkinson’s disease in a new way?
Senior Research Officer
The Walter and Eliza Hall Institute of Medical Research (WEHI)
Dr. Sylvie Callegari completed her PhD at the University of South Australia before moving to Göttingen, Germany for a postdoctoral position in the lab of Prof. Peter Rehling to study how proteins are imported into mitochondria. In 2019, she returned to Australia to join Prof. David Komander's lab at WEHI (the Walter and Eliza Hall Institute of Medical Research) as a senior research officer, where she has been leading the projects on mitochondrial quality control and Parkinson’s disease. She uses a range of techniques in the lab, including cutting-edge cell biology and structural biology techniques and has made key contributions to understanding what the Parkinson’s disease-linked protein PINK1 looks like and how it is activated.
For nearly 20 years, we have known that mutations in the protein PINK1 cause early-onset Parkinson’s disease. Our big breakthrough is that for the first time, we have been able to see what human PINK1 looks like on the surface of damaged mitochondria. Until now, we’ve had to use insect versions of PINK1 to try to understand how PINK1 works, so we’ve never had the complete picture. Our new images reveal human PINK1 sitting on a composition of pores arranged symmetrically on the surface of the mitochondria. This arrangement is more elaborate than anyone had anticipated and even reveals proteins that work together with PINK1, which we previously didn’t know about. So now, with this more complete picture, we have a better understanding of how PINK1 works in humans, and we can see why mutations in different regions of PINK1 cause Parkinson’s disease. Knowing how different mutations cause Parkinson’s may also help us to tailor therapies for patients with PINK1 mutations in the future.
BF:
Senior Science Writer
Technology Networks
Blake pens and edits breaking news, articles and features on a broad range of scientific topics with a focus on drug discovery and biopharma. He earned an honors degree in chemistry from the University of Surrey. Blake also holds an MSc in chemistry from the University of Southampton. His research project focused on the synthesis of novel fluorescent dyes often used as chemical/bio-sensors and as photosensitizers in photodynamic therapy.
How might these findings influence the development of future Parkinson’s treatments?
SC:
Senior Research Officer
The Walter and Eliza Hall Institute of Medical Research (WEHI)
Dr. Sylvie Callegari completed her PhD at the University of South Australia before moving to Göttingen, Germany for a postdoctoral position in the lab of Prof. Peter Rehling to study how proteins are imported into mitochondria. In 2019, she returned to Australia to join Prof. David Komander's lab at WEHI (the Walter and Eliza Hall Institute of Medical Research) as a senior research officer, where she has been leading the projects on mitochondrial quality control and Parkinson’s disease. She uses a range of techniques in the lab, including cutting-edge cell biology and structural biology techniques and has made key contributions to understanding what the Parkinson’s disease-linked protein PINK1 looks like and how it is activated.
These findings are a big leap forward for Parkinson’s drug discovery efforts, especially for those with early-onset Parkinson’s disease due to PINK1 mutations. Our image of PINK1 serves as a blueprint for developing drugs that boost its activity.
Without the ability to see PINK1, we were effectively trying to fix a broken machine while blindfolded. Our recent discovery has removed that blindfold, and now that we can see PINK1, it will be much easier to fix.
Senior Science Writer
Technology Networks
Blake pens and edits breaking news, articles and features on a broad range of scientific topics with a focus on drug discovery and biopharma. He earned an honors degree in chemistry from the University of Surrey. Blake also holds an MSc in chemistry from the University of Southampton. His research project focused on the synthesis of novel fluorescent dyes often used as chemical/bio-sensors and as photosensitizers in photodynamic therapy.
What challenges did you encounter during this research, and how did you overcome them to reach this key discovery?
SC:
Senior Research Officer
The Walter and Eliza Hall Institute of Medical Research (WEHI)
Dr. Sylvie Callegari completed her PhD at the University of South Australia before moving to Göttingen, Germany for a postdoctoral position in the lab of Prof. Peter Rehling to study how proteins are imported into mitochondria. In 2019, she returned to Australia to join Prof. David Komander's lab at WEHI (the Walter and Eliza Hall Institute of Medical Research) as a senior research officer, where she has been leading the projects on mitochondrial quality control and Parkinson’s disease. She uses a range of techniques in the lab, including cutting-edge cell biology and structural biology techniques and has made key contributions to understanding what the Parkinson’s disease-linked protein PINK1 looks like and how it is activated.
To be able to see PINK1, we needed “pieces” of the mitochondrial surface that had PINK1 on them, and we needed a lot of them. Finding a way to get enough human PINK1 has been a problem for decades. To overcome this problem, we used very large amounts of cells (nearly 10 liters of cell culture) from which we would extract damaged mitochondria with PINK1, break up the mitochondria and then collect all the mitochondrial pieces with PINK1 on them. To get enough, this process had to be as efficient as possible. I was lucky in that I had a lot of prior experience in isolating complexes from the surface of mitochondria from my previous training in a mitochondrial lab in Germany, so I already had a head start in coming up with an efficient strategy that allowed us to get enough PINK1 that we could visualize using cryo electron microscopy.
Another problem is that the PINK1 complex that we pull out of cells needs to be stable (it’s hard to take a high-resolution picture of something that moves or falls apart), and so we needed to catch PINK1 at the right point where it is most stable. Experimental strategy was key, and I tried a lot of different experimental conditions to arrive at our final optimized process that resulted in the stable isolation of human PINK1.
Senior Science Writer
Technology Networks
Blake pens and edits breaking news, articles and features on a broad range of scientific topics with a focus on drug discovery and biopharma. He earned an honors degree in chemistry from the University of Surrey. Blake also holds an MSc in chemistry from the University of Southampton. His research project focused on the synthesis of novel fluorescent dyes often used as chemical/bio-sensors and as photosensitizers in photodynamic therapy.
PINK1 has been notoriously difficult to image in the past. What advancements in technology or innovative approaches allowed your team to capture it in such detail?
SC:
Senior Research Officer
The Walter and Eliza Hall Institute of Medical Research (WEHI)
Dr. Sylvie Callegari completed her PhD at the University of South Australia before moving to Göttingen, Germany for a postdoctoral position in the lab of Prof. Peter Rehling to study how proteins are imported into mitochondria. In 2019, she returned to Australia to join Prof. David Komander's lab at WEHI (the Walter and Eliza Hall Institute of Medical Research) as a senior research officer, where she has been leading the projects on mitochondrial quality control and Parkinson’s disease. She uses a range of techniques in the lab, including cutting-edge cell biology and structural biology techniques and has made key contributions to understanding what the Parkinson’s disease-linked protein PINK1 looks like and how it is activated.
The structure of human PINK1 had evaded researchers around the world for decades. Cryo electron microscopy has been revolutionary in solving the structure of protein complexes, in particular membrane complexes like this one, but the main challenge, as described above, was obtaining enough stable PINK1. In recent years, advancements in mammalian protein expression systems, which can be grown at high density and in liter batches, have been a game-changer for producing large amounts of protein in mammalian cells. We used the commercially available Expi293 expression system (Thermo Fisher Scientific) and establishing this system in the lab was my first mission upon embarking on this project. Having an efficient way to grow lots of cells that produce as much PINK1 as possible was the essential first step in our PINK1 isolation protocol.
BF:
Senior Science Writer
Technology Networks
Blake pens and edits breaking news, articles and features on a broad range of scientific topics with a focus on drug discovery and biopharma. He earned an honors degree in chemistry from the University of Surrey. Blake also holds an MSc in chemistry from the University of Southampton. His research project focused on the synthesis of novel fluorescent dyes often used as chemical/bio-sensors and as photosensitizers in photodynamic therapy.
What are the next steps following this discovery? How do you envision the future of Parkinson’s disease therapies evolving?
SC:
Senior Research Officer
The Walter and Eliza Hall Institute of Medical Research (WEHI)
Dr. Sylvie Callegari completed her PhD at the University of South Australia before moving to Göttingen, Germany for a postdoctoral position in the lab of Prof. Peter Rehling to study how proteins are imported into mitochondria. In 2019, she returned to Australia to join Prof. David Komander's lab at WEHI (the Walter and Eliza Hall Institute of Medical Research) as a senior research officer, where she has been leading the projects on mitochondrial quality control and Parkinson’s disease. She uses a range of techniques in the lab, including cutting-edge cell biology and structural biology techniques and has made key contributions to understanding what the Parkinson’s disease-linked protein PINK1 looks like and how it is activated.
There are currently drugs in the clinical pipeline that are believed to increase the activity of PINK1, but without ever seeing where or how these drugs interact with PINK1, we don’t have a complete understanding of how they work. We plan to use our PINK1 isolation method to view these drugs in association with PINK1 to understand how they work. Furthermore, we will also use our PINK1 model to design new drugs that boost PINK1 activity. By boosting PINK1 activity, we help to get rid of toxic, damaged mitochondria in the cell, which would otherwise kill brain cells. This is ultimately what causes Parkinson’s disease, so we need to keep our brain cells alive and well.
