FIGURE 3.

Schematic representation of FtsH-mediated D1 degradation. Upon inactivation, PSII undergo partial disassembly, resulting in transient complex RC47 (PDB:4V62) containing inactivated D1 (pink and purple), D2 (orange), CP47 (green), and small chlorophyll-binding subunits (white). The N-terminal loop of D1 (purple cylinder) is exposed for degradation. The thylakoid FtsH complex (adapted using crystal structure of the whole cytosolic domains of FtsH from T. thermophilus, PDB:2DHR) participates in D1 removal. In the current model, the N-terminal D1 loop feeds through the FtsH linker region (gray dotted lines) and is pulled by the ATPase domains (cyan) down the central pore, and translocated to the protease domain (red). Both RC47 and FtsH complexes are plotted to scale using the lipid membrane as size reference. The missing transmembrane region of FtsH is illustrated as a cartoon: transmembrane helices (gold cylinders) and lumenal region (blue cylinders). The yellow reference rulers represent the dimension (unit: Å) of the Inertia Axis Aligned Bounding Box (IAAB) for the respective protein, which are calculated by Guardado-Calvo’s Python scripts for pymol (https://pymolwiki.org/index.php/Draw_Protein_Dimensions).