Fig. 3: Spectroscopic characterics of HeimdallR1 bound to different xanthophylls.
From: Structural insights into light harvesting by antenna-containing rhodopsins in marine Asgard archaea
a, Fluorescence excitation spectra of HeimdallR1 upon incubation with (orange) or without (purple) lutein (top), diatoxanthin (middle) or fucoxanthin (bottom); emission was recorded at 720 nm. b, The ratios of transient absorption (TA) change in HeimdallR1 with and without lutein (top) and with and without fucoxanthin (bottom) at different excitation wavelengths (425, 450, 465, 480, 545 and 590 nm for lutein and 440, 465, 580, 490, 530, 540, 550 and 600 nm for fucoxanthin) (bars coloured according to the colour of excitation light). The absorption spectra of HeimdallR1 without (purple line) and with (orange line for lutein and coral for fucoxanthin) xanthophylls are overlaid. The red dashed lines indicate no difference between with and without xanthophyll. Tables with the quantum yield (QY) percentages and the pictures of the purified proteins are shown next to the corresponding results. c, Light-minus-dark difference FTIR spectra at 77 K upon illumination of HeimdallR1 with (red) or without (black) fucoxanthin, HeimdallR1 with (red) or without (black) lutein, HeimdallR1 with lutein in H2O (red) or D2O (blue), and Kin4B8-xanthorhodopsin with (green) or without (black) lutein. Hydrated films of lipid-reconstituted protein with H2O are illuminated at 540 nm light (solid lines), which forms the red-shifted K intermediate. Each peak originates from a hydrogen out-of-plane (HOOP) vibration of the retinal chromophore, which shifts upon xanthophyll binding to HeimdallR1, but not to Kin4B8-xanthorhodopsin. One division of the y axis corresponds to 0.0006 absorbance units. LUT, lutein; DIATO, diatoxanthin; FUCO, fucoxanthin.
