The research groups of Janne Ihalainen (University of Jyväskylä) and
Sebastian Westenhoff (University of Gothenburg) have clarified how the
atom structure of bacterial red light photosensors changes when sensing
light. The research reveals structural changes in phytochrome protein
when illuminated.
"The results are a unique demonstration of proteins' ability to
structural changes in different phases of their operation. This helps to
understand how the biological photosensors function. The modelling and
utilisation of protein for other applications becomes much easier when
the protein structures, their changes and the speed of change are
known," says Professor Ihalainen.
The function of few biological photosensors are already utilised in
other fields of science, especially in neurosciences. By utilising
reactions that are controlled by light, it is possible to achieve new
breakthroughs in the cell biological research and, for example, in
medical applications such as in phototherapy and in molecular
diagnostics.
Organisms use photosensor proteins to sense light on different
wavelengths. For example, mammals have rhodopsin proteins in their eyes.
Phytochromes, one of the photosensor proteins of plants, fungi and
bacteria, are sensitive to red light. The function of these photosensors
was known already in 1970s and 1980s, but their molecular-level
operating mechanisms are still unknown.
A pioneering research method
Time-resolved wide-angle X-ray scattering was used to study structural
changes of this rather large protein complex in a solution form. The
technique, TR-WAXS, is relatively new and in this study a successful
combination of the experimental data with the molecular dynamic
simulations enabled to track the detailed structural changes of the
protein.
The crystal structure of bacterial phytochrome changes when illuminated.
"We hope that other groups using TR-WAXS would test similar data-analysis method as well." Ihalainen says.
The light sensitive phytochrome structures were clarified both in a
crystal form and in a solution. From the crystal structures, it is
possible to see that small movement of individual atoms (scale of 0.1 –
0.2 nm) caused by the absorption of light is amplified to large
structural changes (3 nanometres) in the whole protein complex. This
amplification mechanism enables the light induced signal transmission
from one protein to another very quickly and with precise replication
accuracy. In turn, this signal transmission process initiates
cellular-level changes in the organism.
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