During the second summer of research on her Senior Independent Project (SIP), chemistry major Virginia Greenberger (pictured at left) is spending more time in method development than data collection. Here’s the thing about that: “We’ve never done this work before,” says Greenberger. (The other member of “we” is her SIP supervisor, Professor of Chemistry Regina Stevens-Truss; they are trying to develop a method to determine how certain protein pieces—called peptide sequences—kill bacteria.) That “never-having-done-this-work-before” means her SIP research is on the far edge of new discovery, which makes it very cool. But it can also be very frustrating—just one example: the peptide sequences are “sticky” and prone to clump, which makes methods to effectively study them more difficult to develop.
Some back story, which goes back further than last summer. About a decade and a half ago, Stevens-Truss noticed that bacteria she’d altered to produce a certain peptide were being killed by that peptide. Very interesting discovery, on hold for a dozen or so years. Then last summer Stevens-Truss and Greenberger began to study in earnest the protein components responsible for killing the bacteria. These peptide sequences are spiral in shape and carry a positive charge. Shape and charge are matters of chemistry and potential chemical alteration. Summer number one focused on which peptide sequences were the most effective killers of which kinds of bacteria–gram positive (Staph aureus, for example) and gram negative (E-coli, for example). The research team devised a method that uses light to determine the degree to which various peptide sequences inhibit various bacteria. Roughly speaking, “cloudy” or opaque solutions (that block light) mean the bacteria are not much affected by the peptide sequence, but a clear solution indicates significant antibacterial activity. The research could eventually prove very important. Ours is an age of antibiotic resistance. Certain bacteria cause serious infectious diseases, but their reproduction rate (combined with human misuse of antibiotics) selects for resistant strains.
Summer two’s work seeks to repeat (and confirm) the results of last summer and determine how the effective bacterial assassins do their work. How does one determine that? Greenberger is currently working on a method that infuses liposomes with dyes. Liposomes are bag-like structures whose membranes mimic the membranes of cells. A killing mechanism by which the spiral-shaped peptide sequences drill through bacterial cell membranes would be suggested if the lipsome look-alikes suddenly release their dyes. That’s the method on which Greenberger was currently at work at the time of this interview. The working title of her SIP is “Studying Antibiotic Action of Peptide Sequences containing a Cationic Amphipathic Helix Structure.” But that could change, depending on that ever-changing ratio of “cool” to “frustrating.”