Charting the native architecture of Chlamydomonas thylakoid membranes with single-molecule precision: https://elifesciences.org/articles/53740

The cell membrane is not only the boundary of the unit of life, it is also a functional compartment that performs many of the cell’s essential processes, including communication with the environment, transport of molecules and directing a variety of metabolic reactions. Cellular membranes also enable photosynthesis, the transformation of sunlight into life. Improving our understanding of photosynthetic membranes may help solve major global problems, including food scarcity and climate change. At the Helmholtz Pioneer Campus, Ben and his group are using cutting-edge imaging technology  to gain new molecular insights into these life-giving membranes.

In your recent paper, published in eLife, you and your team used a new revolutionary approach to study cellular membranes. Can you tell us more about it?
We use a technique called cryo-electron tomography, which gives us three-dimensional views into native cells with molecular resolution. First, we freeze the cells so quickly that ice crystals cannot form. Next, we thin the cells with an instrument called a focused ion beam. Finally, we transfer these thinned cellular sections into a transmission electron microscope to acquire three-dimensional tomographic images. This imaging is so powerful that we can see the tiny structures of protein complexes inside the native cellular environment. In this study, we developed a new analysis method called a “membranogram”, which shows how membrane proteins are organized within the cellular membranes.      

"Improving our understanding of photosynthetic membranes may help solve major global problems, including food scarcity and climate change."

In your study, you use green algae cells. Why?
The little alga Chlamydomonas, nicknamed “Chlamy”, has been the superhero of most of our studies so far. We call Chlamy a “planimal” because it contains parts from both plants and animals. It also allows imaging of its cellular interior with very high clarity, presumably due to low molecular crowding. Because of this, we have used Chlamy to explore a wide variety of fundamental cellular processes. For this study, we focused on Chlamy’s plant side, an organelle called the chloroplast. The chloroplast is full of sheet-like membrane compartments called thylakoids, which act as the cell’s solar panels, harvesting the energy of light and converting it into biological energy. Using cryo-electron tomography and our “membranogram” analysis, we were able to directly observe how the photosynthetic protein complexes are arranged in native thylakoid membranes.

How are the thylakoid membranes that you are studying relevant to climate change?
The energy produced by light harvesting in thylakoid membranes is used by plants and algae to take carbon dioxide (CO₂) out of the atmosphere and fix it into sugar. This carbon fixation drives the global carbon cycle, assimilating approximately 100 gigatons of carbon each year. By replacing atmospheric CO₂ with oxygen, while simultaneously producing energy-rich biomass, photosynthesis sustains most of the life on Earth, including us! We aim to gain a mechanistic understanding of how cellular architecture directs photosynthesis, which we hope will be useful for engineering plants and algae to fix more CO₂, helping feed the world’s growing population while reducing the atmospheric CO₂ that causes climate change.                      

"Engineering plants and algae to fix more CO_² could help feed the world’s growing population while reducing the atmospheric CO_² that causes climate change."

What’s next for your studies on photosynthesis?
One of our major goals is to understand how the cellular mechanisms of both light harvesting and carbon fixation are affected by changing environmental conditions. This will help us predict how plants and algae will respond to climate change. For example, we plan to build on our current study by tracking how the molecular organization of thylakoid membranes is remodeled in response to changing light. We will expand our studies beyond Chlamy and land plants to explore marine algae, including cyanobacteria, diatoms and corals. These amazingly diverse and poorly understood organisms fix half of all global CO₂. Marine algae are vulnerable to warming, acidification and stratification of the Ocean caused by climate change. They are on the front lines of the battle against global warming, and we want to help them in this fight.