Faculty Bibliography

The membrane domain of human erythrocyte Band 3 protein (M(r) 52,000) was reconstituted with lipids into two-dimensional crystals in the form of sheets or tubes. Crystalline sheets were monolayers with six-fold symmetry (layer group p6, a = b = 170 A, gamma = 60 degrees), whereas the symmetry of the tubular crystals was p2 (a = 104 A, b = 63 A, gamma = 104 degrees). Electron image analysis of negatively stained specimens yielded projection maps of the protein at 20 A resolution. Maps derived from both crystal forms show that the membrane domain is a dimer of two monomers related by two-fold symmetry, with each monomer consisting of three subdomains. In the dimer, two subdomains of each monomer form a roughly rectangular core (40 x 50 A in projection), surrounding a central depression. The third subdomain of the monomer measures approximately 15 x 25 A in projection and appears to be connected to the other two by a flexible link. We propose that the central depression may represent the channel for anion transport while the third subdomain appears not to be directly involved in channel formation

The structure of the light-harvesting chlorophyll a/b-protein complex, a membrane protein serving as the major antenna of solar energy in plant photosynthesis, has been determined at 6 A resolution by electron crystallography. Within the complex, three membrane-spanning alpha helices and 15 chlorophyll molecules are resolved. There is an intramolecular diad relating two of the alpha helices and some of the chlorophylls. The spacing of the chlorophylls suggests energy transfer by delocalized exciton coupling and Forster mechanisms

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 A 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 A 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