Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8648286 | Journal of Structural Biology | 2017 | 10 Pages |
Abstract
Hydration forces between DNA molecules in the A- and B-Form were studied using a newly developed technique enabling simultaneous in situ control of temperature and relative humidity. X-ray diffraction data were collected from oriented calf-thymus DNA fibers in the relative humidity range of 98%-70%, during which DNA undergoes the B- to A-form transition. Coexistence of both forms was observed over a finite humidity range at the transition. The change in DNA separation in response to variation in humidity, i.e. change of chemical potential, led to the derivation of a force-distance curve with a characteristic exponential decay constant of â¼Â 2 Ã
for both A- and B-DNA. While previous osmotic stress measurements had yielded similar force-decay constants, they were limited to B-DNA with a surface separation (wall-to-wall distance) typically > 5 Ã
. The current investigation confirms that the hydration force remains dominant even in the dry A-DNA state and at surface separation down to â¼Â 1.5 Ã
, within the first hydration shell. It is shown that the observed chemical potential difference between the A and B states could be attributed to the water layer inside the major and minor grooves of the A-DNA double helices, which can partially interpenetrate each other in the tightly packed A phase. The humidity-controlled X-ray diffraction method described here can be employed to perform direct force measurements on a broad range of biological structures such as membranes and filamentous protein networks.
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Authors
Ryan Case, Hauke Schollmeyer, Phillip Kohl, Eric B. Sirota, Roger Pynn, Kai E. Ewert, Cyrus R. Safinya, Youli Li,