Several months ago, Justin P. Gallivan gave quite an entertaining seminar for the chemical biology department. While I'm officially a member of the organic division, I really enjoy the biological side of things, so I try to attend these seminars as often as possible (or sometimes I attend them when my boss sends out an email "please attend," which really means "required seminar"). If I remember correctly, Prof. Gallivan did a little "bacteria dance," and if a speaker goes that far to get our attention, he has my respect :o) His lab actually has done some extremely interesting work, and I've been waiting for a publication to come out ever since that seminar.
Last week, the article "Guiding Bacteria with Small Molecules and RNA" finally appeared in JACS. E. coli have 5 chemoreceptor proteins and thus can maneuver their way through complex chemical environments. While they naturally perform chemotaxis toward 30+ compounds, it would be useful in terms of bio-nanotechnology to reprogram these bacteria to respond to new and unique chemical signals. The pathway responsible for converting chemical ligand binding into a change in direction of the bacteria consists of 6 chemotaxis proteins, with the protein known as CheZ ultimately responsible for bacterial motility. With this in mind, Shana Topp from the Gallivan group created a theophylline-sensitive synthetic riboswitch to control translation of CheZ; without theophylline, the conformation of mRNA prevents translation of CheZ, forcing the bacteria to tumble in place. Once theophylline is added to the mixture, the mRNA adapts a different conformation in which the ribosome binding site is open, which allows for expression of CheZ and forward movement of the bacterial cells. Caffeine, which has a structure similar to that of theophylline, did not elicit a response from bacteria, indicating that the observed changes in bacterial motiliy are dependent on the riboswitch. As Topp and Gallivan jokingly state, "E. coli pick decaf!"