Biosynthesis and characterization of novel elastin-based biomaterials and theoretical calculation of proline analogues Open Access

Tian, Ye (2008)

Permanent URL: https://etd.library.emory.edu/concern/etds/9c67wn02m?locale=en
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Abstract


Abstract

Biosynthesis and characterization of fluorinated elastin-mimetic polypeptides and
theoretical calculation of proline analogues

By Ye Tian

Elastin is an important protein that provides connectivity and elasticity in the
extracellular matrix. Elastin-mimetic polypeptides (EMPs) have been widely used as models for
studying the structure and property of native elastin.
In this study, two fluorinated amino acids, 4, 4, 4-trifluorovaline and 3-fluorovaline were
incorporated into the isoleucine and valine codons of an elastin-mimetic polypeptide sequence.
Both the two fluorinated EMPs underwent inverse temperature transitions. Structurally, these two
proteins self-assembled from random coil to type II turn upon temperature increase. In addition,
an EMP sequence comprised of repeating pentapeptide [Val-Pro-Gly-Ala-Gly] was designed to
serve as the sequence for the incorporation of 4, 4-difluoroproline. The gene encoding this
sequence was constructed by recursive directional ligation. Moreover, two plasmin-sensitive
elastin-based triblock copolymers with different size in the mid-block were studied. It was
revealed that these two proteins underwent inverse temperature transition upon a critical
temperature of 19.8 and 20.0 , respectively. This transition was accompanied by a
structure change from random coil to an ordered structure, which was confirmed by the CD
results. Biodegradation of both proteins was demonstrated to be complete within six hours.
Furthermore, two oxidation products of N-acetyl-thioproline-methyl ester were
geometry-optimized by DFT computation. The calculation results revealed that the anti product
preferred a C- exo pucker and a trans amide bond while the syn product preferred a C- endo
pucker and a cis amide bond. It was shown that both the gauche effect between the sulfoxide
bond and the amide nitrogen as well as the n* interaction between the nonbonding oxygen
and the carbonyl group of the ester contributed to the conformational preferences.

Table of Contents



Table of contents


Chapter 1. General Introduction .................................................................................1
Chapter 2. Biosynthesis and characterization of fluorinated elastin-mimetic
polypeptides.................................................................................................9
Chapter 3. Design and construction of elastin-mimetic polypeptide gene suitable
for the study of 4, 4-difluoroproline incorporation ............................26
Chapter 4. Characterization of biodegradable materials based on elastin-mimetic
polypeptide.................................................................................................38
Chapter 5. DFT calculation of the conformational preference of thioproline
derivatives ................................................................................................51
Chapter 6. Conclusions ..............................................................................................69















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