HIGH-RESOLUTION ELECTRON CRYSTALLOGRAPHY OF LIGHT-HARVESTING CHLOROPHYLL-A/B-PROTEIN COMPLEX IN 3 DIFFERENT MEDIA

Large two-dimensional crystals of the light-harvesting chlorophyll a b-protein complex (LHC-II) from the photosynthetic membrane of pea chloroplasts were grown by a new method from detergent solution. The structure of these crystals was examined by electron crystallography, using three different media to preserve high-resolution detail: vitrified water, glucose and tannin. The crystals diffracted electrons to at least 3.2 Å resolution in all three media, R-factors between the three data sets of electron diffraction amplitudes ranged from 6.4% to 14.3%. Fourier difference maps were generated and compared to a projection map of the complex at 3.4 Å resolution. No significant differences were found, proving that all three media preserved the native structure of LHC-II at high resolution. The probability of recording high-quality electron diffraction patterns with tannin was 90%. With glucose and water this probability was lower by a factor of 10 to 20, suggesting that tannin may be preferable as a preserving medium for sensitive biological specimens. © 1991.