Introduction: Life as Movement
Scientists often describe life as a series of chemical reactions. But Pallav Kosuri, Ph.D., describes life as movement. Chemical reactions drive the movement of atoms, proteins, cells, and bodies—without movement, there is no life. 'If you don't know how something moves, you don't know what it does,' says Kosuri. 'And if you want to understand, manipulate and alter the function of molecules, understanding their physical movements is just as important as understanding their chemical reactions. The difference is: We have a comprehensive catalog of the chemical reactions, while the mechanical side is still the Wild West.'
Kosuri's lab at the Salk Institute is setting out to change that. In a new study published in Cell Reports Methods, they introduce ORBIT, a method that uses DNA origami to build fluorescent nanostructures for visualizing molecular movements. This innovative approach overcomes long-standing technical limitations, allowing researchers to track the rotation of a single RNA polymerase molecule as it reads DNA with base-pair resolution over hours—a feat previously impossible.
The Challenge of Measuring Molecular Movement
Fluorescence microscopy is a powerful technology, but its observation times are limited by the photobleaching of fluorescent tags. Over time, these tags inevitably go dark, restricting measurements to mere seconds. This has made it difficult or impossible to study molecular movements over extended periods, particularly processes like transcription that occur over minutes to hours.
To address this, Kosuri and his team developed a 'dye-cycling' strategy for ORBIT. This technique constantly replenishes fluorescent tags, extending the measurement window from seconds to hours. By doing so, they can now observe molecular dynamics in real time with unprecedented precision.
How ORBIT Works
ORBIT leverages DNA origami, a method that uses DNA building blocks to create custom, self-assembling nanostructures. These nanostructures can be designed to attach to specific proteins and amplify their movements. In this case, the researchers built a rotor-like structure with a corkscrew stem that attaches to RNA polymerase, an X-shaped handle, and a fluorescent dye probe. As the polymerase moves along the DNA, the rotor amplifies the motion, making it detectable under a microscope.
The key innovation is the dye-cycling mechanism. Instead of relying on a single fluorescent tag that fades, ORBIT continuously introduces fresh dye molecules, keeping the signal bright for extended periods. This allows the team to track the rotation of RNA polymerase as it transcribes genes, base pair by base pair.
Implications for Understanding Gene Transcription
Gene transcription is a fundamental process in which RNA polymerase reads DNA and produces RNA. While the chemical steps of transcription are well understood, the mechanical aspects—how the polymerase moves, rotates, and interacts with DNA—remain largely unexplored. ORBIT provides a window into these dynamics, offering insights that could lead to new therapeutic strategies.
For example, understanding how transcription machinery moves could help researchers design drugs that target specific steps in the process, potentially treating diseases caused by transcriptional dysregulation. Moreover, the ability to observe molecular movements in real time could be applied to other protein-DNA interactions, opening new avenues in molecular biology.
Broader Applications and Future Directions
Beyond transcription, ORBIT's dye-cycling strategy could be adapted to study a wide range of molecular interactions. The team envisions applications in drug delivery, lab-on-a-chip devices, and foundational biological discovery. By providing a tool to visualize molecular movement, ORBIT could help bridge the gap between chemical and mechanical understanding of life.
Kosuri's lab is already planning to expand ORBIT's capabilities. They aim to increase the resolution and sensitivity of the technique, as well as apply it to other molecular motors and enzymes. The ultimate goal is to create a comprehensive atlas of molecular movements, similar to the catalog of chemical reactions that already exists.
Conclusion
The development of ORBIT marks a significant step forward in the field of molecular biophysics. By enabling long-duration, high-resolution tracking of molecular movements, it offers a new lens through which to view the mechanical underpinnings of life. As Kosuri puts it, understanding movement is key to understanding function. With ORBIT, researchers are now equipped to explore the 'Wild West' of molecular mechanics, potentially unlocking new insights into biology and medicine.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
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