Synchrotron X-ray radiation damage in protein structure determination: why do we care?

About

Structural biology relies on X-ray crystallography to provide much of the three-dimensional information on macromolecules (proteins, DNA, RNA) that informs biological function. Our research focusses on developing improved methods for macromolecular crystallography (MX) to enable problems not previously accessible to structure solution to be tackled. A notable example of this has been progress in finding protocols to cryocool protein crystals prior to 100 K data collection to reduce the rate of radiation damage (RD) by around a factor of 70 compared to the rate at room temperature. However, the RD observed at modern synchrotron sources during diffraction experiments at 100 K is still a limiting problem, since it can mislead the experimenter when interpreting the biology relevant to the mechanism of action of the protein. Particularly interesting is MX at X-ray Free electron lasers where 'diffraction before destruction' is possible.

In a second research strand, we use proton induced X-ray emission (microPIXE) to unambiguously identify metals in proteins using the known sulphur concentration as an internal standard. Metalloproteins comprise over 30% of proteins, with approximately half of all enzymes requiring metal to function. Accurate identification of these metal atoms and their environment is a prerequisite to understanding biological mechanism, but other than microPIXE there are no routine analysis methods with the sensitivity and quantitative accuracy to do this. I will summarise our recent rather concerning measurements on 102 metalloproteins deposited in the Protein Data Bank (PDB).

A persistent theme of this talk will be the interdisciplinarity of using of nuclear physics techniques to elucidate investigations in structural biology.

Bio: Elspeth Garman is a Professor of Molecular Biophysics Emerita at Oxford University. She started her working life aged 18 as a volunteer secondary school teacher in Swaziland (now Eswatini), Southern Africa. Following a…