Two-dimensional crystallization and preliminary structure analysis of LHC-II from cucumber and spinach

Large and well-ordered two-dimensional (2D) crystals of the light-harvesting chlorophyll a/b protein complexes (LHC-II) from cucumber and spinach chloroplasts were produced by the so-called batch method. The twodimensional structures of these crystals were examined at about 1.5 nm resolution by electron microscopy and image processing. The projection maps showed that there were similar, but not identical, structure features between two different LHC-II complexes. A cmparison between 2D crystal formations of the two different LHC-II complexes was done and some factors affecting 2D crystallization of the membrane proteins were analyzed. The relations of the structures of the LHC-II complexes to their polypeptide components and Chl a/b ratio were also discussed.