Abstract
Ycf12 is a recently identified low-molecular mass trans-membrane protein of photosystem II (PSII), and its location is unknown in the current crystal structure. We purified PSII dimers from a Ycf12-deletion mutant of Thermosynechococcus elongatus, crystallized, and analyzed the structure of the mutant PSII. Our result showed that Ycf12 is located in the periphery of PSII close to PsbK and PsbZ, and corresponded to an unassigned helix X1 in the 3.0 Å structure reported by the Berlin group. Combining our previous results that X2 is PsbY, it is strongly suggested that the remaining unassigned helix X3 in the 3.0 Å structure corresponds to PsbX. We also purified PSII from a PsbZ deletion mutant, and crystallized PSII from the mutant. The crystals obtained had significantly different unit cell constants than those of wild type, indicating the participation of this subunit in joining the two PSII dimers within the wild type crystals
