Time-resolved X-ray solution scattering observations of light-induced structural changes in sensory rhodopsin II

Area of Science:

• Biophysics
• Microbiology
• Structural Biology

Background:

• Unicellular organisms sense environmental changes via signaling cascades.
• Sensory rhodopsin II (SRII) is a blue-light receptor in archaea, mediating negative phototaxis.
• Understanding SRII's signal transduction is key to microbial environmental responses.

Purpose of the Study:

• To characterize the mechanism of signal transduction by SRII using time-resolved X-ray solution scattering (TR-XSS).
• To investigate how light-induced structural changes in SRII are affected by its transducer protein, HtrII.

Main Methods:

• Time-resolved X-ray solution scattering (TR-XSS) was employed to capture dynamic structural changes.
• TR-XSS difference data were analyzed to model protein conformational alterations.
• Structural predictions of the SRII:HtrII complex were integrated with experimental data.

Main Results:

• Light induces outward movement of helices E and F in SRII.
• This movement magnitude is consistent whether HtrII is present or absent.
• Modest changes were also observed in helices C and extracellular regions of D and E.

Conclusions:

• TR-XSS reveals SRII's light-induced conformational changes involve specific helix movements.
• The transducer protein HtrII does not significantly alter the primary light-driven helix displacement.
• These findings offer insights into how SRII communicates signals to HtrII for phototaxis.