Physicists from the University of Illinois at Urbana-Champaign have developed a technique that can measure nano-scale motion considerably more precisely than any other method.
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 [Taekjip Ha, U. of Illinois professor of physics –ed.] 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. Therefore, by monitoring the brightness of the two dyes, the researchers can determine the motion of the molecule.
The optical trap, on the other hand, functions somewhat like the fictional tractor beam in Star Trek. In this case, a focused laser beam locks onto a microsphere attached to one end of the molecule to be studied. The optical trap can then pull on the molecule like a pair of tweezers.