Structural and functional studies on Ycf12 (Psb30) and PsbZ-deletion mutants from a thermophilic cyanobacterium.

Ycf12 (Psb30) and PsbZ are two low molecular weight subunits of photosystem II (PSII), with one and two trans-membrane helices, respectively. In order to study the functions of these two subunits from a structural point of view, we constructed deletion mutants lacking either Ycf12 or PsbZ from Thermosynechococcus elongatus, and purified, crystallized and analyzed the structure of PSII dimer from the two mutants. Our results showed that Ycf12 is located in the periphery of PSII, close to PsbK, PsbZ and PsbJ, and corresponded to the unassigned helix X1 reported previously, in agreement with the recent structure at 2.