Expanding Barrels, Twisting Tubules

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Science  16 Jun 2000:
Vol. 288, Issue 5473, pp. 1935
DOI: 10.1126/science.288.5473.1935a

Barrel-like protein architectures support a wide range of biological functions, from transport across membranes to catalysis of metabolic reactions. Previously, Baumeister and Matile synthesized tetrameric barrels that self-assemble from solution and that are stable in detergent-free water. The two types of component molecules consist of chains of benzene rings (rigid rods) with complementary tripeptide ligands that adhere to form small _-sheets. These authors have now expanded these structures to form hexameric barrels by replacing half of the leucine residues with bulkier tryptophans. The hexamers have an interior diameter of about 2 nanometers, which may be useful for encapsulating molecules such as biological chromophores.

One strategy for synthesizing nanostructures is to assemble layers of oppositely charged particles. Lvov et al. have imaged subtle charge patterns in microtubules formed from lipids containing diacetylenic groups by attaching charged particles (silica nanospheres) that then can be imaged by transmission electron microscopy. For microtubules containing only a neutral zwitterionic lipid, particles attached to the ends of the tubules. However, adding a small fraction (2%) of anionic lipid allowed the helical twist of the microtubules to be seen readily. This approach could be used to assemble more intricate structures that take advantage of the microtubule helicity.—JU; PDS

Chem. Commun.2000, 913 (2000); Langmuir, in press.

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