‘Comet water’ ions found in bacterial protein
30 Jan 2013
Novel sample preparation processes and diffractometers have uncovered hydronium ions in rubredoxin.
Rubredoxin is a light weight iron-sulphur protein found in some of the earliest, most basic forms of life- notably bacteria and archaea.
These ions, commonly found in comet tails or interstellar space clouds, have been found to be involved in crucial interactions with the protein.
The results combine the use of one of the world’s most sophisticated diffractometers with a novel sample preparation process whereby the protein’s hydrogen atoms are replaced with the heavier isotope, deuterium, greatly enhancing the visualisation of hydronium ions.
Neutrons are particularly good in studying biological materials since they are highly sensitive to lighter atoms such as hydrogen - strongly complementing the capabilities of synchrotron X-rays which are more sensitive to heavier elements.
However in the past neutron scientists have run into difficulties when studying proteins due to excessive levels of background noise in the measured data, drastically limiting the scope of analysis work.
The curved ’banana’ shape covers a wide angle around the sample allowing the acquisition of remarkably high-quality data
This problem can be avoided by replacing the hydrogen atoms in the protein by deuterium.
In response, a team of scientists at Keele University in the UK and at the Institut Laue-Langevin (ILL) have developed a unique Deuteration Laboratory that allows biological macromolecules to be deuterated in a way that optimises the quality of the data collection and of the final results.
Deuterated rubredoxin was produced and the scattering (diffraction) experiments carried out on the ILL’s world leading monochromatic neutron beamline.
Uniquely amongst neutron diffraction instruments, the detector on D19 has a curved ’banana’ shape that covers a wide angle around the sample allowing the acquisition of remarkably high-quality data.
The team characterised both the reduced and oxidised forms of the protein at near-atomic resolution. Surprisingly, the results showed the presence of numerous hydronium (H3O+) ions within the protein.
Whilst H3O+ ions have been identified in chemical systems and in one protein, this is the first time they have been found in a redox protein where they are likely to be deeply implicated in charge transfer.
