Spontaneous activation of visual pigments in relation to openness/closedness of chromophore-binding pocket
Wendy Wing Sze Yue,
Rikard Frederiksen,
Xiaozhi Ren,
Dong-Gen Luo,
Takahiro Yamashita,
Yoshinori Shichida,
M Carter Cornwall,
King-Wai Yau
Affiliations
Wendy Wing Sze Yue
Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, United States; Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, United States; Biochemistry, Cellular and Molecular Biology Graduate Program, Johns Hopkins University School of Medicine, Baltimore, United States
Rikard Frederiksen
Department of Physiology and Biophysics, Boston University School of Medicine, Boston, United States
Xiaozhi Ren
Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, United States; Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, United States
Dong-Gen Luo
State Key Laboratory of Membrane Biology, Peking University, Beijing, China; McGovern Institute for Brain Research, Peking University, Beijing, China; Center for Quantitative Biology, Peking University, Beijing, China; Peking-Tsinghua Center for Life Sciences, Beijing, China; College of Life Sciences, Peking University, Beijing, China
Takahiro Yamashita
Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
Yoshinori Shichida
Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
M Carter Cornwall
Department of Physiology and Biophysics, Boston University School of Medicine, Boston, United States
Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, United States; Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, United States; Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, United States
Visual pigments can be spontaneously activated by internal thermal energy, generating noise that interferes with real-light detection. Recently, we developed a physicochemical theory that successfully predicts the rate of spontaneous activity of representative rod and cone pigments from their peak-absorption wavelength (λmax), with pigments having longer λmax being noisier. Interestingly, cone pigments may generally be ~25 fold noisier than rod pigments of the same λmax, possibly ascribed to an ‘open’ chromophore-binding pocket in cone pigments defined by the capability of chromophore-exchange in darkness. Here, we show in mice that the λmax-dependence of pigment noise could be extended even to a mutant pigment, E122Q-rhodopsin. Moreover, although E122Q-rhodopsin shows some cone-pigment-like characteristics, its noise remained quantitatively predictable by the ‘non-open’ nature of its chromophore-binding pocket as in wild-type rhodopsin. The openness/closedness of the chromophore-binding pocket is potentially a useful indicator of whether a pigment is intended for detecting dim or bright light.
