Date of Graduation

5-2015

Document Type

Thesis

Degree Name

Bachelor of Science

Degree Level

Undergraduate

Department

Chemistry & Biochemistry

Advisor

Koeppe, Roger E.

Reader

Hagstrom, Fran

Second Reader

Sakon, Joshua

Third Reader

Harriss, Edmund

Abstract

The vital role that membrane proteins play in cell mechanisms and the inner workings of disease in our bodies has been universally accepted. Thus, the study of protein-membrane and transmembrane interactions has become increasingly significant in understanding these membrane proteins. Synthetic model peptides, such as GWALP23 (acetyl-GGALW5LALALALALALALW19LAGA-amide)—designed at the University of Arkansas and composed of the amino acid residues of glycine (G), alanine (A), leucine (L) and tryptophan (W) —provide a favorable “host” framework for investigations of the influence of chosen “guest” amino acids. For example, it is of interest to know the consequences of having a third, centrally located, tryptophan (Trp) within the hydrophobic core of a well characterized, anchored, transmembrane helix. It is crucial to note that the orientation and rotation of GWALP23 are sensitive to single-residue replacements, in part because the membrane-spanning helix exhibits only limited dynamic averaging of solid-state NMR observables such as the deuterium (2H) quadrupolar splitting. A single Trp residue was introduced in the 12th or 13th position of GWALP23, and specific deuterated alanine labels (2H-Ala) were included as probes within the core helical sequence. The 2H quadrupolar splittings from solid-state NMR spectra of GWALP23-W12 and GWALP23-W13 show that the peptide remains helical and retains a dominant preferred tilted transmembrane orientation (similar to GWALP23) in lipid bilayer membranes of DLPC, DMPC, and DOPC. Modified Gaussian and semi-static treatments of the peptide dynamics yield similar conclusions. While a central Trp at position 12 or 13 does not alter the characteristics of bilayer-spanning GWALP23, incorporation of the peptide helix into the bilayer membrane becomes more difficult. The properties of Trp4,5 GWALP 23 are also being investigated for comparison with the highly dynamic Tyr4,5 and the less dynamic Phe4,5 peptides. Preliminary results through solid-state 2H NMR reveal Trp4,5 to be more dynamic than Phe4,5 and less dynamic than Tyr4,5. Deuterium labels at Ala3 and Ala21 reveal possible fraying of the ends of selected helices in bilayers comprised of lipids of acyl chains of differing lengths. The partial helix unwinding could help to stabilize the peptide with a central Trp residue.

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