Recycling, an important mechanism in cells
Using a bottom-up approach, scientists have highlighted the important role of recycling in the constant renewal of structures of actin, a protein that plays an essential role in eukaryotic cells.
Actin is one of three filamentous proteins that form the cytoskeleton, a structure that helps maintain cell shape and organization and performs other essential functions. Actin plays many roles: it gives the cell its shape, allows it to move, or helps it divide. In cells, actin comes in different forms and actin structures are constantly assembling and disassembling to adapt to their environment.
“We can think of a cell as a smart house, whose shape remains constant but whose bricks are constantly renewed to adapt to storms and heat,” explained Alexandra Colin, a researcher at CEA Grenoble in France, in Manuel Théry and Laurent Blanchoin’s team.
However, how these actin structures in cells can be both stable and renewed with a limited amount of components had been little studied until now. Alexandra and her colleagues, therefore, sought to answer this question using a bottom-up approach. Their results were published in March 2023 in The EMBO Journal.
Reconstitution of a three-step cycle: assembly, disassembly, and recycling
In collaboration with researchers from New York University and the University of Helsinki, they reconstituted a dynamic system of actin in vitro, thus outside a cell, in a closed system with a limited reservoir of components and energy. Through this experiment, they showed that recycling was a key step in enabling multiple assembly/disassembly cycles.
“We performed the experiment with a particular actin structure, actin monomers, and showed that in order to be reused in the cycle, the monomers had to be recycled, i.e. recharged with energy thanks to a protein called CAP.”
The role of energy consumption and component ageing on the lifetime of living systems
But the team made another discovery. By pushing the system to its limit, they discovered the root cause of the assembly and disassembly process stopping.
“Our system lasted five to six hours, which had never been done before. I’m proud that we were able to keep the system dynamic for so long because this allowed us to realize that this stoppage was not due to a lack of energy as one might think, but to the actin monomers which oxidize with time and can no longer be recycled.
“Actin oxidizes in cells, but not as quickly. Our study shows that the mechanisms by which it prevents actin ageing in cells deserve further study.”
What are the next steps?
After studying actin monomers, the team plans to test other actin structures and study how different forms of actins coexist and share resources while being dynamic.
Recycling of the actin monomer pool limits the lifetime of network turnover
Alexandra Colin, Tommi Kotila, Christophe Guérin, Magali Orhant-Prioux, Benoit Vianay, Alex Mogilner, Pekka Lappalainen, Manuel Théry, Laurent Blanchoin
The EMBO Journal (2023) e112717