Microtubules (MT) are biological nanotubes composed of α-/β- tubulin heterodimers. One of three major components of the cytoskeleton, MTs are essential for cell structure, cell division, and intracellular transport in eukaryotes. While healthy neuronal axons contain long, stable microtubules, the axons of patients diagnosed with Alzheimer’s disease show abnormally depolymerized microtubules. Tau is a MT-associated protein that is abundant in neuronal axons and is crucial for stabilizing microtubules and regulating microtubule-microtubule interactions. Post-translational modifications of tau, such as phosphorylation, can alter its electrostatic properties, leading to changes in Tau-MT and MT-MT interactions. While tau phosphorylation is tightly regulated in healthy cells, its misregulation has been implicated in neurodegenerative diseases. However, it remains poorly understood as to how and why altered electrostatics drive these “tauopathies”.

Our experiments use in vitro MT assemblies to study the underlying physics of tau-mediated MT interactions. Building on previous studies, we are currently focusing on the effects of chemically altered tau. We have spent the summer purifying various tau isoforms with point mutations that convert specific Ser/Thr residues to aspartate. This “pseudo-phosphorylation” helps us study the electrostatic effects of the disease-state phosphorylated tau. In order to study these protein assemblies, we first create plasmids and transform competent E. coli cells. Then we grow large batches of bacteria to overexpress our protein, which we harvest and purify. Future MT polymerization studies in the presence of our pseudo-phosphorylated tau should lay the groundwork for understanding the physical properties governing healthy and diseased axonal MT structures.