Date on Master's Thesis/Doctoral Dissertation

12-2020

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Degree Program

Chemistry, PhD

Committee Chair

Wittebort, Richard

Committee Co-Chair (if applicable)

Lee, Donghan

Committee Member

Lee, Donghan

Committee Member

Maurer, Muriel

Committee Member

Mueller, Eugene

Committee Member

Zhang, Xiang

Author's Keywords

elastin; NMR; disorder; compaction

Abstract

Minielastins are elastin-based proteins with alternating hydrophobic and cross-link modules similar to tropoelastin. Tropoelastin is the ~70 kDa soluble monomeric precursor of elastin. The extracellular matrix protein, elastin provides elasticity to tissues and organs such as lungs, arteries and ligaments. The elastic properties of natural elastin are believed to be entropic in origin. In vivo, the elastin matrix is approximately 50% water by weight. Without water, elastin is brittle and hard. Minielastins, like tropoelastin, undergo a liquid-liquid phase transition upon an increase in temperature. Factors such as hydrophobicity, chain length and concentration affect the coacervation temperature, Tc. The coacervation temperature were modulated by changing the number of hydrophobic repeats and the length of cross-link modules. Each hydrophobic repeat, VPGVGG and APGVGV, decreases Tc by 1.7 and 1.5 °C, respectively. Also, increasing the temperature and pressure causes the hydrodynamic radii of minielastins to shrink, similar to other disordered proteins. Elastin-like biomaterials exhibit a great potential in tissue engineering and drug delivery. Therefore, it is important, for a wide array of applications, to understand the relationship between protein sequence, structure and mechanical properties of elastin biomaterials. To obtain residue specific information using nuclear magnetic resonance (NMR) spectroscopy, simplified hydrophobic and cross-link modules were designed based on the predominant 6-residue repeats found in tropoelastin exon 20 (VPGVGG) and 24 (APGVGV) hydrophobic modules and the consensus cross-link motif, A4/5KA2/3K, found in the natural elastin. In this study, the hydrophobic modules, responsible for the self-assembly of elastin-like proteins, were found to be highly disordered. Also, the cross-link modules are disordered, but when flanked by hydrophobic modules they are weakly a-helical. These conclusions are supported by analysis of complete assignment of backbone 1H, 13C and 15N chemical shifts and 15N spin relaxation measurements (R1, R2 and NOE) with spectral density modeling. These results show that the amplitude of dynamics in the hydrophobic modules approach that of a flexible polymer chain with chain dynamics on two timescales, ~1­ – 2 ns and ~30 – 80 ps. Well-ordered regions were not found. Finally, the ability of minielastins to form insoluble cross-linked products have proved its potential as an elastic biomaterial.

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