Date of Award

Fall 2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular Biophysics and Biochemistry

First Advisor

Koleske, Anthony

Abstract

Abl family kinases are believed to serve as central signaling nodes to transduce signals from upstream receptors to downstream signaling and cytoskeletal-associated proteins. Genetic studies in Drosophila indicate that Abl2 interacts functionally with microtubules (MTs), but the underlying mechanism(s) is (are) completely unclear. Here, I report that Abl2 directly binds MTs and tubulin to regulate MT dynamics. Abl2 binds with MTs via the C-terminal half, which is also mediated by the phosphorylation level of the N-terminus. Abl2 recognizes different MT lattice states, with a higher preference for GMPCPP-MTs than GDP-MTs. Abl2 also binds tightly to tubulin dimers, which is mediated by amino acids 688-924 in the C-terminus. As a naturally existing isoform, Abl2Δ688-790 loses its binding ability to tubulin dimers. I found that Abl2 promotes MT assembly and nucleation, as measured by the turbidity change. Interestingly, Abl2-eGFP formed spherical condensates in a concentration- and salt-dependent manner, which can recruit tubulin into Abl2:tubulin co-condensates. Co-condensation of Abl2 and tubulin further facilitates MT nucleation. Single-MT filament TIRF microscopy revealed that Abl2 increases MT elongation rate, which is consistent with the cellular observation that MTs have slower growth rates in Abl2 knockout cells. Lastly, the loss of the Abl2 in cells leads to an abnormally high cell migration speed, which can be partially rescued by the C-terminal half that mediates the MT binding. Collectively, my data suggest the molecular mechanism that Abl2 acts as a MT nucleator and regulator to modulate MT dynamics and coordinate cellular behaviors.

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