Oncology & Cancer

Canceling cancer with T cells

What if we could engineer our immune system to make the human body better at fighting cancer? Professor Roy Mariuzza is part of a major research effort aimed at doing just that. An expert in the structural biology of immune ...

Oncology & Cancer

Receptor structure reveals new targets for cancer treatment

A molecule known as anaplastic lymphoma kinase (ALK) is a driver of several cancers, including pediatric neuroblastoma, B-cell lymphomas, and myofibroblast tumors. But for years much about this molecule—its role in the ...

Medical research

Scientists accelerate path to drugs for COVID-19

Scientists at The University of Manchester have developed a more efficient method to produce medicines that are in development for the treatment of COVID-19, cancer and other diseases that affect many of the world's population.

Medical research

Viral 'molecular scissor' is next COVID-19 drug target

American and Polish scientists, reporting Oct. 16 in the journal Science Advances, laid out a novel rationale for COVID-19 drug design—blocking a molecular "scissor" that the virus uses for virus production and to disable ...

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X-ray crystallography

X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and diffracts into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their disorder and various other information.

Since many materials can form crystals — such as salts, metals, minerals, semiconductors, as well as various inorganic, organic and biological molecules — X-ray crystallography has been fundamental in the development of many scientific fields. In its first decades of use, this method determined the size of atoms, the lengths and types of chemical bonds, and the atomic-scale differences among various materials, especially minerals and alloys. The method also revealed the structure and functioning of many biological molecules, including vitamins, drugs, proteins and nucleic acids such as DNA. X-ray crystallography is still the chief method for characterizing the atomic structure of new materials and in discerning materials that appear similar by other experiments. X-ray crystal structures can also account for unusual electronic or elastic properties of a material, shed light on chemical interactions and processes, or serve as the basis for designing pharmaceuticals against diseases.

In an X-ray diffraction measurement, a crystal is mounted on a goniometer and gradually rotated while being bombarded with X-rays, producing a diffraction pattern of regularly spaced spots known as reflections. The two-dimensional images taken at different rotations are converted into a three-dimensional model of the density of electrons within the crystal using the mathematical method of Fourier transforms, combined with chemical data known for the sample. Poor resolution (fuzziness) or even errors may result if the crystals are too small, or not uniform enough in their internal makeup.

X-ray crystallography is related to several other methods for determining atomic structures. Similar diffraction patterns can be produced by scattering electrons or neutrons, which are likewise interpreted as a Fourier transform. If single crystals of sufficient size cannot be obtained, various other X-ray methods can be applied to obtain less detailed information; such methods include fiber diffraction, powder diffraction and small-angle X-ray scattering (SAXS). In all these methods, the scattering is elastic; the scattered X-rays have the same wavelength as the incoming X-ray. By contrast, inelastic X-ray scattering methods are useful in studying excitations of the sample, rather than the distribution of its atoms.

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