Date of Graduation

5-2020

Document Type

Thesis

Degree Name

Bachelor of Science

Degree Level

Undergraduate

Department

Chemistry & Biochemistry

Advisor/Mentor

Koeppe, Roger

Committee Member/Reader

Thallapuranam, Suresh

Committee Member/Second Reader

Ivey, Mack

Committee Member/Third Reader

Paul, David

Abstract

Transmembrane proteins make up critical components of living cells. Protein function can be greatly impacted by the charged state of its respective components, the side chains of amino acid residues. Thus far, in the lipid membrane, little is known about the properties of residues such as glutamic acid. To explore these properties, I have included glutamic acid in a suitable model peptide-lipid system for fundamental biophysical experiments. Within the system, I have placed a glutamic acid residue instead of leucine in the L14 position of the helical hydrophobic peptide GWALP23 (acetyl-GGALWLALALALAL14ALALWLAGA-amide). Substitutions of glutamine and aspartic acid serve as controls for the properties of the peptide helix in lipid bilayer membranes. The GWALP23 peptide derivatives are placed in various lipid bilayer environments.

Specifically, I investigated the impact of glutamic acid (position E14) when differently charged lipids are present in the bilayer. The underlying importance is to understand the charged or neutral state behavior of glutamic acid under conditions where it is important for the functioning of several types of membrane proteins, such as ion channels, drug transporters and others. For the experimental plan, core alanine resides of GWALP23 were labeled with deuterium to enable detection of helix characteristics by solid-state 2H NMR spectroscopy. The peptide-lipid samples included primarily the neutral lipid DMPC, 1,2-dimyristoylphosphatidylcholine, (with 14-carbon acyl chains), along with 10% of a charged lipid. For each membrane system, I confirmed lipid bilayer formation for the particular peptide-lipid mixture by solid-state 31P NMR. The charged lipids consisted of the negatively charged lipid DMPG, 1,2-dimyristoylphosphatidylglycerol, and the positively charged lipid DMTAP, 1,2-dimyristoyl-3-trimethylammonium-propane. These charged lipids were found to influence the properties of the GWALP23 helix when E14 was present. DMTAP, in particular, improves the 2H NMR spectra and the prospects for characterizing helix dynamics when a glutamic acid residue is present. While some experiments were cut short due to a global emergency, the results show promise for characterizing glutamic acid in model helices and actual membrane proteins.

Keywords

GWALP23, NMR Spectroscopy, Lipid Bilayer, Computational Chemistry

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