Conformational Regulation and Signaling of an Atypical Integrin αvβ8

Author

Guannan SongFollow

Degree

Doctor of Philosophy (PhD)

Department

Biological Science

Document Type

Dissertation

Abstract

Integrins are heterodimeric transmembrane proteins that play important roles in various biological processes. Most integrins serve as adhesion molecules and transmit bidirectional signals through global conformational changes. However, integrin β₈ is distinctive in structure and function. Its cytoplasmic domain lacks the conserved protein-binding sequence, which is important in transmitting inside-out signals, suggesting that integrin β₈ may have a different activation mechanism or lack such signaling. In addition, the ligand-binding or activating metal ion Mn²⁺ does not induce a global conformational change in integrin β₈.

It is unclear how different domains affect integrin α_vβ₈ global conformation, ligand binding ability and signaling on the cell surface. In the first study, we designed cysteine mutations to determine whether the association of the α_v and β₈ lower legs affected its ligand binding. We showed that disulfide bonded mutants bound ligands with similar level as the wild-type protein, suggesting that α_vβ₈ ligand binding did not require lower leg disassociation. We further showed that the N-glycosylation mutant at the interface between the β I and hybrid domains did not affect ligand binding, suggesting that the α_vβ₈ open headpiece was not present on the cell surface. Our study indicates that α_vβ₈ integrin may adopt only one state, and the association of two lower legs might be important for stabilizing integrins in the extended conformation.

Furthermore, we designed experiments to study how different β₈ domains affect its unique conformation and function. We found that the β₈ EGF domains increased integrin ligand binding ability and contributed to its extended conformation. By comparison, the β₈ transmembrane and cytoplasmic domains had little effect on ligand binding or global conformation. The β₈ EGF and transmembrane domains did not affect integrin-mediated cell adhesion, cell spreading, focal adhesion formation or colocalization of integrin with other proteins, but the cytoplasmic domain had a defective effect on outside-in signaling. Our results showed that different domains of β₈ play various roles on its unique conformation, ligand binding and signaling. The extended structure and high ligand-binding affinity of integrin α_vβ₈ make it ideal for encountering and binding ligands expressed on an opposing cell or in the extracellular matrix.

Date

12-7-2020

Recommended Citation

Song, Guannan, "Conformational Regulation and Signaling of an Atypical Integrin αvβ8" (2020). LSU Doctoral Dissertations. 5428.
https://repository.lsu.edu/gradschool_dissertations/5428

Committee Chair

Luo, Bing-Hao

DOI

10.31390/gradschool_dissertations.5428