Researchers use the force of a focused laser beam to make precise models of cytoskeletons in living cells.
(Nanowerk News) Networks of protein fibers play important roles in living cells. To understand the dynamical behavior of these networks, model networks are needed to perform in vitro studies. However, fabrication of protein networks similar to those in cells has proved difficult, as current methods could affect the biological function of these proteins – ultimately impacting our understanding of any findings.
Formation of a protein fiber assembly by focused laser irradiation. (Video: Yoshikawa Lab)
The shape of living cells is determined by an internal network of protein fibers called a cytoskeleton. The cytoskeletal structure is dynamic, as the key nodes for cell function shift over time. One such cell function can be witnessed with motor proteins, which convert chemical energy into mechanical work. These proteins walk along cytoskeletal tracks to drive muscle contraction and transport components across the cell.
In vitro models have been constructed to understand the structure–motion relationship of cytoskeletal networks, meaning how the organization of molecules affects its dynamics. Some models have been formed via self-organization, which is the spontaneous arising of structures through interactions between protein fibers.
However, the arrangement and evolution of the network structure cannot be controlled using self-organization alone. To tackle this, ultraviolet or blue light has been employed in research to spark the formation of a protein network at specific locations.
The native biomolecules forming the network need to be chemically modified to respond to light, which could affect their biological functions and, crucially, any resulting conclusions. Light triggers organization effectively, but can cause interference when fluorescence imaging is used for visualization.
To circumvent these problems, the team tested whether the photophysical effects of a focused laser beam could be used to fabricate a fibrous protein network in a non-invasive manner.
“The electric field of the focused laser beam generated an optical force on very small protein molecules,” explains lead author, Hiroshi Yoshikawa. “The optical force caused these molecules to accumulate at the laser focus without bringing them into physical contact. As a result, highly ordered arrangements of protein-fiber networks formed.”
The fabricated networks exhibited various dynamic motions similar to those observed in living cells, such as translational motion and flagella-like rotation.
“Our approach does not require chemical modification of molecules, reducing the likelihood that native biomolecules lose their biological functions”,” reports Hiroshi Yoshikawa. “Additionally, the laser wavelength used is in the near-infrared regime, which does not overlap with the wavelengths of light sources used for fluorescence imaging.”
This technology could be applied in biological fields to determine mechanisms involving the cytoskeleton, such as cell division, migration, and adhesion. Interestingly, the technology could also have applications beyond biology, including creating protein-based actuators (robotic “muscles”).
