FIGURE 10.

Comparison of dimeric PSII projection maps to visualize differences between C. merolae and T. elongatus at the subunit level. A and C, side and lumenal top view projection maps of the C. merolae PSII dimer particles, respectively. In A, the 1.9 Å structure of PSII from T. vulcanus (1) (Protein Data Bank coordinates 3ARC) was overlaid onto the top view EM projection map of the C. merolae complex. The D1 (PsbA) and D2 (PsbD) subunits are colored in light blue and dark blue, respectively. The CP43 (PsbC) and CP47 (PsbB) subunits are depicted in red and magenta, respectively. The PsbZ subunit is highlighted in black. The extrinsic subunits PsbV, PsbU, and PsbO are shown in orange, green, and yellow, respectively. For clarity, all remaining subunits are shown in gray. The overall size of PSII dimer particles in A is 21.2 × 11 nm. B, a high resolution structure of T. vulcanus PSII seen from aside and truncated at 8 Å resolution (1). D and E, top and side views of T. elongatus PsbZ-less PSII dimers (82); F, top view of T. elongatus PSII containing PsbZ (83). The dotted line correlates the position of an additional density with the CP43 subunit in the side view map (B) and in the top view (D). *, location where PsbQ′ is located in the C. merolae PSII complex and is absent in the T. vulcanus and the T. elongatus complex. Scale bar, 10 nm.