When proteins are made inside cells, genetic information (in the form of messenger RNA) must be “translated” into specific sequences of amino acid building blocks. Accurate translation is essential to the health of the cell, and the idea that “one gene gives one protein” emerged very early in the development of the field of molecular biology. Researchers in the Center for the Science and Engineering of Materials (CSEM) at the California Institute of Technology are changing that idea. By expressing carefully designed artificial genes in bacterial cells, CSEM investigators have created artificial proteins that show considerable promise as surgical materials and as matrices for regenerative medicine. Furthermore, by engineering the enzymes that control protein synthesis, they’ve expanded the set of amino acids that can be used to make proteins. They’ve shown, for example, that the natural amino acid phenylalanine (F) can be replaced by para-azidophenylalanine (pAzF), a photosensitive derivative. The inclusion of pAzF renders proteins susceptible to light-induced crosslinking, and because pAzF and phenylalanine compete with one another in the translation step, one can use a single gene to direct the synthesis of not just one protein, but of a whole family of related proteins. The figure shows measurements of the stress-strain behavior of one such family, in which the relative amounts of phenylalanine and pAzF were systematically varied. As the relative amount of pAzF in the protein increases, the proteins crosslink more tightly and give rise to stiffer materials. Thus while a “literal translation” of the messenger RNA would yield just one material, the introduction of pAzF enables the synthesis of many new materials on the same RNA template. The stiffness of the material (and other important properties) can therefore be matched closely to the demands of the intended application.
“Woe to the makers of literal translations, who by rendering every word weaken the meaning.” Voltaire, On Tragedy (1732); quoted in The Columbia World of Quotations (1996).
Normally, well, flaws are bad. But through a newly developed technique of microcontact insertion printing, Penn State researchers can use the flaws in a selfassembled monolayer to place individual isolated molecules in predetermined patterns on a gold substrate. A self-assembled monolayer is a tightly packed wellordered array of molecules covering a surface, all tilted to one side like a cornfield in a windstorm. But the direction of the tilt is different in different parts of the sample. Where two domains of different tilt collide, a defect results, a molecule-sized hole in the monolayer. By judiciously building these defects into the surface, and then filling them selectively by pressing the surface with a patterned stamp, we can place isolated molecules in predesigned nano-scale or micro-scale patterns. Using a series of stamps, each embossed with a different pattern and coated with a different target molecule, we can build up a complex multicomponent pattern. If these isolated target molecules are designed to capture specific analytes, then complex solutions containing biomolecules or environmental contaminants can be separated and analyzed by this nanoscale “smart surface.”
A University of Chicago MRSEC team led by Philippe Guyot-Sionnest and Woowon Kang have been investigating the transport properties of colloidal quantum dots under magnetic field [1].
Myelin figures are long thin cylindrical structures that grow when water is added to the concentrated lamellar phase of certain surfactants such as soap. The Sidney Nagel and Tom Witten groups at the University of Chicago developed a method to produce isolated myelin figures, based on previous investigations of ring stain formation pioneered at the MRSEC. This allowed them to study their growth and stability in detail.
