Extended Data Fig. 6: Absorption spectra of purified HeimdallR1 with and without lutein or fucoxanthin and pH dependence of the absorption.
From: Structural insights into light harvesting by antenna-containing rhodopsins in marine Asgard archaea
a, UV–vis absorption spectra: HeimdallR1 alone (left, purple), HeimdallR1 complexed with lutein (middle, yellow), and HeimdallR1 complexed with fucoxanthin (right, red). To estimate the λamax of the retinal in HeimdallR1, the absorption spectra of pure xanthophylls (blue) were subtracted from those of HeimdallR1 complexed with each xanthophyll (green). Since the peak positions of pure xanthophylls slightly differ from those complexed with HeimdallR1, the spectra of pure xanthophylls were manually shifted so that the peak positions coincides between the spectra of pure xanthophylls and HeimdalR1-xanthophyll complexes. Pictures of purified proteins are shown next to the corresponding results. b, Absorption spectra (top) and the different absorption spectra (bottom), and c, pH titration curves for the calculation of pKa were measured depending on acidic (left) and alkaline (right) pH changes. The red-shifted (red arrow) and blue-shifted (blue arrow) absorption spectra at each pH are indicated by arrows. The pH titration curves were analyzed using the Henderson–Hasselbalch equation86. d, Color protein changes upon acid-basic titration.
