RESUMO
Photosystem II from transplastomic plants of Nicotiana tabacum with a hexahistidine tag at the N-terminal end of the PsbE subunit (α-chain of the cytochrome b(559)) was purified according to the protocol of Fey et al. (BBA 12:1501-1509, 2008). The protein sample was then subjected to two additional gel filtration runs in order to increase its homogeneity and to standardize the amount of detergent. Large three dimensional crystals of the core complex were obtained. Crystals of one of its chlorophyll binding subunits (CP43) in isolation grew in very similar conditions that differed only in the concentration of the detergent. Diffraction of Photosystem II and CP43 crystals at various synchrotron beamlines was limited to a resolution of 7 and 14 Å, respectively. In both cases the diffraction quality was insufficient for an unambiguous assignment of the crystallographic lattice or space group.
