Macromolecular structural dynamics visualized by pulsed dose control in 4D electron microscopy
Macromolecular conformation dynamics, which span a wide range of time scales, are fundamental to the understanding of properties and functions of their structures. Here, we report direct imaging of structural dynamics of helical macromolecules over the time scales of conformational dynamics (ns to subsecond) by means of four-dimensional (4D) electron microscopy in the single-pulse and stroboscopic modes. With temporally controlled electron dosage, both diffraction and real-space images are obtained without irreversible radiation damage. In this way, the order-disorder transition is revealed for the organic chain polymer. Through a series of equilibrium-temperature and temperature-jump dependencies, it is shown that the metastable structures and entropy of conformations can be mapped in the nonequilibrium region of a "funnel-like" free-energy landscape. The T-jump is introduced through a substrate (a "hot plate" type arrangement) because only the substrate is made to absorb the pulsed energy. These results illustrate the promise of ultrafast 4D imaging for other applications in the study of polymer physics as well as in the visualization of biological phenomena.
Additional Information© 2011 National Academy of Sciences. Freely available online through the PNAS open access option. Contributed by Ahmed H. Zewail, March 1, 2011 (sent for review February 4, 2011). Published online before print March 28, 2011. We thank Dr. J. S. Baskin for the fruitful comments and reading of the manuscript. We gratefully acknowledge very helpful and thorough reports by Professors Edwin L. Thomas and M. Muthukumar. A.H.Z. thanks Professor David Tirrell for his insightful remarks. This work was supported by National Science Foundation Grant DMR-0964886 and Air Force Office of Scientific Research Grant FA9550-07-1-0484 in the Physical Biology Center for Ultrafast Science and Technology at Caltech supported by the Gordon and Betty Moore Foundation. Author contributions: O.-H.K., V.O., and A.H.Z. designed research, performed research, contributed new reagents/analytic tools, analyzed data, and wrote the paper. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1103109108/-/DCSupplemental.
Published - Kwon2011p13712P_Natl_Acad_Sci_Usa.pdf
Supplemental Material - pnas.1103109108_SI.pdf