Sungchul Hohng, Ruobo Zhou, Michelle K. Nahas, Jin Yu, Klaus Schulten, David
M. J. Lilley, and Taekjip Ha.
Fluorescence-force spectroscopy maps two-dimensional reaction
landscape of the Holliday junction.
Science, 318:279-283, 2007.
HOHN2007
Despite the recent advances in single molecule manipulation techniques, a biologically important regime of detecting subtle conformational changes under weak forces is still out of reach. We developed a hybrid scheme combining force and fluorescence which allowed us to examine the effect of sub-pN forces on the nanometer scale motion of the Holliday junction (HJ) at 100 Hz bandwidth, a task unachievable for purely mechanical methods. The HJ is an exquisitely sensitive force sensor whose force response is amplified with an increase in its arm lengths. This is a lever-arm effect at the smallest length scale ever demonstrated. Mechanical interrogation of the HJ in three different directions helped elucidate the structures of the transient species populated during its conformational changes. Our work represents a significant advance on the previous state of the art of dynamic force spectroscopy which were limited to higher forces or a single reaction coordinate.
