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Surface Density-Dependent Interactions between Photoactivated Sensory Rhodopsin 2 and Its Transducer
Tatsuya Sakamoto1, Jingyi Tang1, Soichiro Kato1
1Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.
ACS Omega
|February 23, 2026
Summary
Sensory rhodopsin 2 (pSRII) and its transducer (pHtrII) initiate signal transduction via membrane conformational changes, not HAMP domain interactions. This study reveals the primary mechanism of light signal transfer in this microbial photosensor system.
Area of Science:
- Microbiology
- Biophysics
- Structural Biology
Background:
- Sensory rhodopsin 2 (pSRII) and its transducer (pHtrII) form a complex to regulate microbial flagellar rotation in response to light.
- Previous studies suggest conformational changes in pSRII's F helix trigger pHtrII helix rotation, but the role of the HAMP domain in signal transduction remains unclear due to its flexibility.
Purpose of the Study:
- To investigate the role of the HAMP domain in the protein-protein interactions and signal transduction between pSRII and pHtrII.
- To elucidate the structural changes occurring in the pSRII-pHtrII complex under physiological membrane conditions.
Main Methods:
- Surface-enhanced infrared spectroscopy (SEIR) was used to analyze structural changes in pSRII and pSRII fused with different domains of pHtrII (including or excluding the HAMP domain).
- Experiments were conducted under physiological membrane orientation to mimic in vivo conditions.
Main Results:
- The light-induced spectral changes in the amide I region of pSRII-pHtrII complexes were attenuated in a surface-density-dependent manner.
- This attenuation was similar whether the HAMP domain was present or absent, indicating it does not significantly influence the conformational changes in the membrane region.
Conclusions:
- The primary signal transduction from pSRII to pHtrII occurs through conformational changes within the membrane-bound regions of the complex.
- The HAMP domain is not essential for the initial light-induced conformational changes mediating signal transfer between pSRII and pHtrII.
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