Figure 7.

Schematic Models of PSII in Cyanobacteria and Plants.

The core PSII subunits (D1, D2, CP43, and CP47, shown as green boxes) provide the primary binding sites for the Mn-Ca-Cl cluster (red, blue, and white dots, respectively) and extrinsic proteins (shown in red, blue, or purple). Based on the suggested stoichiometry for plant PSII, there should be one PsbP and PsbQ molecule for every PSII core (top). Cyanobacterial PSII has five extrinsic subunits in the thylakoid lumen, with PsbP ant55d PsbQ anchored to the membrane. PsbP (blue) is substoichiometric, so not every PSII core has an associated PsbP protein.