Peptides are Subject of Matthew Baxter '11 and Jason McGavin '12 Research

Jason McGavin '12 and Matthew Baxter '11.
Jason McGavin '12 and Matthew Baxter '11.
Jason McGavin '12 and Matthew Baxter '11 understand that a peptide's structure can say a lot about how it functions in the body. This summer, they are studying two versions of the peptide Piscidin – Piscidin 1 and Piscidin 3. They will work alongside Associate Professor of Chemistry Myriam Cotten, whose previous work in this field has illustrated that there is a distinct difference between them. 

Piscidin 1 is capable of killing bacteria, but also destroys red blood cells, which are the body's principal means of delivering oxygen to all parts of the body. Piscidin 3, on the other hand, can select the bacteria from the mass of red blood cells. Thus, it tries to avoid harming the red blood cells and seeks out the bacteria instead. The result is a much lower rate of red blood cell loss. The disparity between the peptides' physical properties might be able tell the students why one demonstrates this kind of selective attention while the other doesn't. 

Peptides are made up of amino acids, and the peptide Piscidin happens to have 22 of them. Of these, four are histidine amino acids. But that figure only applies to Piscidin 1. Piscidin 3, by constrast, has only three histidines. Histidine is one of the 20 amino acids that are found in proteins. For infants especially, it is an essential amino acid that aids in nutrition starting at an early age. 

All types of Piscidin contain 20 common amino acids, but the students are keeping a steady eye on histidine in particular. While Baxter investigates one of the amino acids that are found in both samples, McGavin is going to research the particular histidine that Piscidin 3 lacks. If they can pinpoint the properties of this histidine, then they might be able to hypothesize why the two versions are so similar yet very different. 

In amino acid land, opposites don't attract. The two students say that one reason why Piscidin 1 is more likely to kill whatever crosses its path is because it is hydrophobic. Hydrophobic molecules repel water because water is electrically polarized and hydrophobes are not. If you think back to high school introductory chemistry, bonds come in two genres: polar and non-polar. An asymmetric molecule signals a red flag for polarity, and another characteristic of hydrophobic molecules is that they are non-polar and prefer other neutral molecules or non-polar solvents. Water is no such molecule. Baxter and McGavin will also study the hydrophobia of Piscidin 1 and Piscidin 2's contrasting hydrophilic nature. 

Their procedure is long and begins with the isotope Nitrogen-15. Baxter and McGavin will have it protected and sent to the University of Texas, where experts will synthesize it and put it into a protein. After the students receive it, they will travel to Florida with several other Hamilton chemistry students. Florida is a gold mine of NMR (Nuclear Magnetic Resonance) machines that will record the change in pH level in the peptide. As they slowly administer higher and higher pH levels, the students will wait for the moment that the Histidine changes from positive to neutral. This information could tell them how Histidine behaves within the protein and how it would react to different pH levels in the body. 

The findings will be just one segment of a greater project that Cotten has been working on for seven years. The research this summer is merely one variation on a theme – the team hopes to contribute to Cotten's body of knowledge on anti-microbial peptides. Their work is also a continuation of a recently graduated senior's thesis. 

Baxter is interested in going to graduate school after Hamilton, and McGavin thinks that he will take the medical school route. McGavin also noted that their project is really focused on biochemistry, and one of the difficult aspects of majoring in science is sorting through the copious options – a chemistry student might go into research or become a doctor. Or he could switch gears and study biochemistry, like they are doing this summer. And sometimes a student will decide that his calling is science education – a profession on which Hamilton prides itself.
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