Date of Graduation

5-2020

Document Type

Thesis

Degree Name

Bachelor of Science

Degree Level

Undergraduate

Department

Chemistry & Biochemistry

Advisor/Mentor

Roger, Koeppe

Committee Member/Reader

Paul, David

Committee Member/Second Reader

Lehmann, Michael

Committee Member/Third Reader

Lessner, David

Abstract

Transmembrane proteins constitute about 30% of the proteins in a mammalian cell and are involved in major biological processes. The dynamic properties of membrane proteins and the ionization states of particular side chains are important for biological function. The biophysical properties of membrane proteins nevertheless can be difficult to decode, particularly for glutamic acid in the lipid environment of cell membranes. To study the ionization of glutamic acid in transmembrane peptides, guest glutamic acid residues were substituted into the well-defined model helix of GWALP23 (acetyl-GGAL4WLALALALALAL16ALWLAGA-amide). These guest residues were placed at position L16 or L4 and specific 2H-labeled alanine residues were incorporated in the central helix to enable detection by solid-state NMR. These chemically synthesized GWALP23 derivatives were placed in lipid membranes with 90% zwitterionic and 10% negatively or positively charged lipids, DMPG or DMTAP, buffered at pH 3.0, 6.1 or 8.0 in deuterium-depleted water. Lipid bilayer alignment was confirmed with 31P NMR. The core alanines of the GWALP23 E16 helix give distinguishable 2H quadrupolar splittings at pH 6.1 with both positive and negatively charged lipids. Samples containing DMTAP had identical splittings from pH 3-8, indicating a lack of titration or lack of helix response. However, the samples with DMPG did not maintain distinguishable quadrupolar splittings above or below pH 6. The findings with DMPG are puzzling yet may reveal changes in helix aggregation or dynamics. Ongoing investigations of GWALP23 with E4 are focused on better understanding of the pH dependence of helix properties. The present results and anticipated future results are important for understanding membrane protein function.

Keywords

Biochemistry, Biophysics, Solid-State NMR, glutamic acid, GWALP23

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