2

A simple question to which I am yet to find an answer. I have not found any papers which would go into detail about it, there is some stuff on protein damage in x-ray crystallography but they are looking at the crystallized proteins, I am interested in "natural" proteins...

leb
  • 73
  • How on Earth is that a "simple" question? What is exactly the type of experimental set-up you have in mind? – gatsu Jul 10 '14 at 08:51
  • One of the basic assumptions in protein crystallography is that there is no important difference between 'natural' and crystallized proteins. Chances are that the results on damage in crystals are applicable to 'natural' proteins. – taupunkt Jul 10 '14 at 09:08
  • In protein crystallography, you can tolerate some degree of chain scission since (1) much of the protein will be held in place because of the surrounding crystal matrix (all the other proteins), and (2) the contribution of those proteins that are cut to the total diffraction is some diffuse background and won't impact the interpretation of the diffraction pattern. They do account for that in the analysis. – Jon Custer Jul 10 '14 at 14:06
  • Forgot I asked here. I was able to play around with some BSA and zap various amounts of Gy into it (up to 1000Gy), but we only had some basic varian spectrometers and and FLS 920 http://www.edinburghphotonics.com/spectrometers/fls920-fluorescence-spectrometers/. Saw absolutely no difference between irradiated and control BSA spectra... – leb Nov 04 '14 at 10:31

1 Answers1

1

X-ray and gamma rays do cause damage do the proteins, however it is important to notice that they are different things and the chemical mechanisms for causing damage to proteins are usually different, although both end up causing damage by ionization processes.

About x-rays

The damage of x-rays in proteins is relevant in the context of cristallography:

The majority of 3D structures of macromolecules are currently determined by macromolecular crystallography, which employs the diffraction of X-rays on single crystals. However, during diffraction experiments, the X-rays can damage the protein crystals by ionization processes, especially when powerful X-ray sources at synchrotron facilities are used. This process of radiation damage generates photo-electrons that can get trapped in protein moieties. The 3D structure derived from such experiments can differ remarkably from the structure of the native molecule.[1]

This is a problem because bigger proteins need more powerful X-ray sources for higher resolution of the crystal structure, which however causes more damage to the protein. To alleviate the problem, the samples are kept at cryogenic temperatures, but this does not solve the problem completely. For this reasons it is important to analyse different crystals and use other techniques that can provide redundant information about tertiary structure of proteins for confirmation such as NMR (Nuclear magnetic resonance spectroscopy).

About gamma rays

Gamma rays, on the other hand, usually affect proteins on contexts like radioactive exposure (in space or contact with radioactive sources).

High-energy electrons and gamma rays ionize molecules at random along their trajectories. In each event, chemical bonds are ruptured, releasing radiolytic products that diffuse away. A solution of macromolecules is mostly water whose principal radiation products are H(+) and OH(-). These can diffuse to and react with macromolecules; this indirect action of radiation is responsible for 99.9% of the damage to proteins.[2]

This is not necessarily bad as gamma rays are commonly used for desinfection [3]. However, it is a big concern for astronauts and during radioactive incidents.

[1] Carugo, Oliviero, and Kristina Djinović Carugo. "When X-rays modify the protein structure: radiation damage at work." Trends in biochemical sciences 30.4 (2005): 213-219.

[2] Kempner, E. S. "Effects of high‐energy electrons and gamma rays directly on protein molecules." Journal of pharmaceutical sciences 90.10 (2001): 1637-1646.

[3] Ridenour, Gerald M., and Edward H. Armbruster. "Effect of high-level gamma radiation on disinfection of water and sewage." Journal (American Water Works Association) 48.6 (1956): 671-676.

Odano Naotake
  • 366