TUBULAR CRYSTALS OF A PHOTOSYSTEM-II CORE COMPLEX

An oxygen evolving photosystem II core complex containing all three ex trinsic proteins (33, 23, 17 kDa) was isolated from spinach and recons tituted into tubular two-dimensional crystals of 72.9 nm diameter and 1-2 micrometers length. While the 17 and 23 kDa polypeptides were lost during crystallization, the extrinsic 33 kDa protein was retained. Th e optical spectrum of the crystallized core was characteristic of an i ntact PSII core complex. Immunoelectron microscopy revealed that the l umenal surface of the PSII complex was exposed at the outside of the c ylindrical tubes. The projection of the complex was determined from fl attened tubular crystals by negative stain electron microscopy and ima ge analysis to 2.0 nm resolution. Rhombic unit cells (a = 16.2 nm, b = 13.7 nm; gamma = 142.4 degrees) contained one PSII complex. (C) 1996 Academic Press Limited