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“Nobody has succeeded in this before”

Plants and bacteria adapt to light environment by using various photoreceptor proteins. Phytochromes are a group of photoreceptors that respond to red and far-red light. The function of phytochromes have been studied extensively. Still, their full and biologically relevant structures have remained elusive.

Now, full-length structures of a model bacterial phytochrome, DrBphP, from Deinococcus radiodurans have been revealed in two activity states. “Although many groups have tried, nobody has succeeded to solve a crystal structure of a full-length phytochrome,” explains docent Heikki Takala from the Ģ��ֱ��. “We therefore decided to apply cryo-electron microscopy to this model phytochrome.”

Light-triggered structural changes revealed by cryogenic electron microscopy

An international team, including the groups of Dr. Heikki Takala and Prof. Janne Ihalainen from the Ģ��ֱ��, have now successfully uncovered the structure of DrBphP. By using single particle cryo-electron microscopy (cryo-EM), they found out that the structure of the full-length phytochrome is symmetrical and relatively well-defined dimer in the dark-adapted state. However, when illuminated with red light, its output histidine kinase module becomes asymmetrical and less defined.

Unlike predicted in previous studies, the light-induced structural changes in the photosensory module were small but amplified only at the output module. “These results show that almost non-existent structural changes in the regulatory domains can cause large changes elsewhere, giving valuable information about signal propagation and allostery in sensory proteins“, concludes Prof. Janne Ihalainen, one of the senior scientists in the team.

Reference:

• The paper ‘Structural mechanism of signal transduction in a phytochrome histidine kinase’ can be freely accessed online at .

Contacts:

• Heikki Takala, Docent in Department of Biological and Environmental Science, University of Jyvaskyla, +358 46 923 6211, heikki.p.takala@jyu.fi
• Janne A. Ihalainen, Professor in Department of Biological and Environmental Science, University of Jyvaskyla, +358 40 024 7979, janne.ihalainen@jyu.fi