Possible Terahertz Signals in Visual Processes

Rhodopsin consisting of an opsin and its ligand (i.e., retinal) is critical to vision formation. When the rhodopsin is stimulated by light, the retinal undergoes a structural isomerization that activates the process of visual signaling. This photoisomerization involves the interaction between the opsin and retinal. Studies have shown that terahertz (THz) spectroscopy is a potential non-invasive means to identify the structure and rotation-vibration of biomolecules. More specifically, the rotational spectra of opsin and retinal in the low frequency THz band might indicate their dynamic conformations. Herein, we calculated the rotational inertia and spectra of the opsin and retinal. We found that both the opsin and retinal exhibit main absorption peaks in the low frequency THz band, which correspond to the collective rotational modes of the molecules. Thus, we suggest that the interactions and structural changes between opsin and retinal can be characterized by low-frequency THz spectra. The study of the rotational spectra of opsin and retinal is important for understanding the function of the visual system, disease mechanisms, and the development of drug therapy. It sheds light on the structure and interactions of these molecules and advances the field of vision science and medicine.