CHAMPAIGN, Ill. A hybrid device combining force and fluorescence developed by researchers at the University of Illinois has made possible the accurate detection of nanometer-scale motion of biomolecules caused by pico-newton forces.
By combining single-molecule fluorescence resonance energy transfer and an optical trap, we now have a technique that can detect subtle conformational changes of a biomolecule at an extremely low applied force, said U. of I. physics professor Taekjip Ha, the corresponding author of a paper to appear in the Oct. 12 issue of the journal Science.
The hybrid technique, demonstrated in the Science paper on the dynamics of Holliday junctions, is also applicable to other nucleic acid systems and their interaction with proteins and enzymes.
The Holliday junction is a four-stranded DNA structure that forms during homologous recombination for example, when damaged DNA is repaired. The junction is named after geneticist Robin Holliday, who proposed the model of DNA-strand exchange in 1964.
To better understand the mechanisms and functions of proteins that interact with the Holliday junction, researchers must first understand the structural and dynamic properties of the junction itself.
But purely mechanical measurement techniques can not detect the tiny changes that occur in biomolecules in the regime of weak forces. Ha and colleagues have solved this problem by combining the exquisite force control of an optical trap and the precise measurement capabilities of single-molecule fluorescence resonance energy transfer.
To use single-molecule fluorescence resonance energy transfer, researchers first attach two dye molecules one green and one red to the molecule they want to study. Next, they excite the green dye with a laser. Some of the energy moves from the green dye to the red dye, depending upon the distance between them. The changing ratio of the two intensities indicates the relative movement of the two dyes
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University of Illinois at Urbana-Champaign