Fig. 4: Structure of CAL-II and its interactions with adjacent subunits.

a Overall structure and unsharpened cryo-EM map of CAL-II. The NTD and CTD are indicated. b Cartoon representation of one RsPSII-CAC module. CAL-II, helix C of CAC5, and CP47 are colored in blue, magenta, and salmon, respectively, whereas other subunits are colored in pink. Chls 301 and 302 of CAL-II and Chl a615 of CAC6 are shown in green color and labeled. c Interactions between CAL-II (shown in cartoon mode) and adjacent subunits (shown in surface mode). Subunits involved in the interaction with CAL-II are labeled and colored as in Fig. 1c. Other subunits are shown in white. d–j Hydrogen bond interactions between NTD of CAL-II and PsbH (d), CTD of CAL-II and PsbH (e), CTD of CAL-II and CP47 (f), CTD of CAL-II and D1 (g), CTD of CAL-II and CP43 (h), CTD of CAL-II and PsbT (i) and CTD of CAL-II and PsbM/PsbM’ (j). The PsbM from another PSII-CAC module (PsbM’) is colored in light yellow in (j). Hydrogen bonds are shown in blue dashed lines and the distances (Å) are labeled in the vicinity.