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. 2020 Mar 17;295(19):6754–6766. doi: 10.1074/jbc.RA120.012950

Figure 4.

Figure 4.

Absorption spectra of Cys variants of ToTCCP indicates an essential role for the TCCP-signature cysteine in forming the B-absorbing 15Z dark-state. Absorption spectra of PCMs of ToTCCP, canonical Cys variants, C257A (A) and C257S (B), and TCCP-signature cysteine variants, C258H (C), C258S (D), C258D (E), C258I (F), C258F (G), and C258Y (H), at pH 8 incorporating PCB are shown for 15Z dark-states (blue) and 15E photoproducts (orange). The loss of the canonical Cys in C257A/C257S variants yields a B-absorbing 15Z species that affords a stable B-absorbing 15E state because of the apparent stability of the C10 linkage. The loss of the TCCP-signature Cys (C258H/C258S/C258D/C258I/C258F/C258Y) yields red-absorbing variants in both 15Z and 15E states due to the loss of the C10 thioether linkage.