Date of Graduation

12-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor/Mentor

Thallapuranam, Suresh

Committee Member

Sakon, Joshua

Second Committee Member

Koeppe, Roger E. II

Third Committee Member

Adams, Paul D.

Fourth Committee Member

Millett, Francis S.

Fifth Committee Member

Chen, Jingyi

Keywords

Enhanced bioactivity; Fibroblast growth factor 1; heparin; heparin binding pocket; Increased stability; site directed mutagenesis

Abstract

Fibroblast growth factors (FGFs) are involved in various cellular processes such as cell growth,proliferation, differentiation, migration, angiogenesis, wound healing and embryonic development. Human acidic fibroblast growth factor (hFGF1) binds non-selectively to all the four FGF-receptors and is therefore considered as a powerful mitogen with broadest specificity. However, pharmacological applications of hFGF1 are restricted due to the low thermal stability of the growth factor. hFGF1 has low thermodynamic stability under physiological temperatures which leads to impairment of cellular signaling process thereby preventing its potential mitogenic properties. hFGF1 has a heparin binding pocket at the C-terminus which comprises of positively charges residues. The interaction between the positively charged amino acids lead to electrostatic repulsions, thereby rendering instability. To overcome this instability, hFGF1 binds to the glycosaminoglycan, heparin which decreases the repulsion (s) between the positively charged residues. However, binding of heparin poses a challenge for the use of hFGF1 in wound healing. Thrombin converts fibrinogen to fibrin and works as first line of defense by blocking the loss of blood. Intriguingly, thrombin also binds to heparin. Studies on wtFGF1 have demonstrated the presence of secondary thrombin cleavage site in hFGF1. Thus, thrombin is known to cleave hFGF1 at Arg 136 and render it biologically inactive. Usually, it is considered that dependency of hFGF1 to heparin increases the plausibility of thrombin-induced degradation of the growth factor. To tackle these downfalls, I have designed and constructed several point mutations in hFGF1 to improve the thermal stability and cell proliferation ability and to subside the heparin binding affinity of the growth factor.

In this dissertation, I studied single, double, triple, quadruple, and penta variants of Q54P, S61L, H107S, K126N, and R136E and examined the thermal stability, bioactivity, and heparin dependency of the protein. These studies indicate that site - directed mutagenesis in hFGF1 can impact the inherent stability of the growth factor and role of heparin in hFGF1-FGFR receptor interaction and activation.

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