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Natural Pore-Forming Proteins

Reconstructed electron density maps
Paul A. Heiney and Virgil Percec

Natural pore-forming proteins and their remodeled structures exhibit a diversity of biological and biologically inspired functions such as transmembrane channels, viral helical coats, reversible encapsulation, stochastic sensing, and pathogenic and antibiotic activity. Attempts to study synthetic porous protein mimics have been limited by the difficulty of forming periodically ordered structures amenable to diffraction analysis. We have studied new synthetic pore-forming dendritic dipetides [(4-3,4-3,5-4)12G2-CH2-Boc-L-Tyr-L-Ala-OMe and (4-3,4-3,5-4)12G2-CH2-Boc-D-Tyr-D-Ala-Ome]. These dendrons self-assemble into asymmetric elliptical and symmetric circular columns which in turn selforganize into rectangular or hexagonal columnar periodic arrays. The transition from symmetric to asymmetric columns is mediated by the thermal history of the sample, thus providing a means to control pore size and shape. We developed a method to determine the dimensions of these columns by the reconstruction of the small-angle powder X-ray diffractograms.

Figure: Reconstructed electron density maps for (4-3,4-3,5-4)12G2CH2Boc-L-Tyr-L-Ala-OMe centered rectangular phase using measured diffraction amplitudes (a) and amplitudes calculated from shell model (b).