Three-dimensional double helical DNA structure directly revealed from its X-ray fiber diffraction pattern by iterative phase retrieval.

Coherent diffraction imaging (CDI) allows the retrieval of an isolated object's structure, such as a macromolecule, from its diffraction pattern. CDI requires the fulfillment of two conditions: the imaging radiation must be coherent and the object must be isolated. We discuss that it is possible to directly retrieve the molecular structure from its diffraction pattern, which was acquired neither with coherent radiation nor from an individual molecule. This is provided that the molecule exhibits periodicity in one direction, as in the case of fiber diffraction. We demonstrate that, when we apply iterative phase retrieval methods to a fiber diffraction pattern, the repeating unit; that is, the molecule structure, can directly be reconstructed without any prior modeling. For example, we recover the the DNA double helix's structure in three-dimensions from its two-dimensional X-ray fiber diffraction pattern, Photograph (Photo) 51, which was acquired in Raymond Gosling and Rosalind Franklin's famous experiment at a resolution of 3.4 Å.