Microtubule associated protein (Tau) is found predominantly in the central neural system and its major function is to promote assembly and to stabilize neuronal microtubules. Six isoforms of Tau were identified in humans that are differentiated by the exclusion or inclusion of exons 2, 3, and 10. Tau-441 is the longest of Tau isoforms, consisting of 441 amino acids with molecular mass of 45.8 kDa. Under physiological conditions Tau can undergo abnormal phosphorylation, truncation, or other modifications that result in the protein detachment from microtubules. These modified Tau molecules can self-associate and form different types of aggregates including neurofibrillary tangles (NFTs) found in brains of patients with neurodegenerative diseases such as Alzheimer’s disease.
Figure 1. Human Tau-441 on SDS-PAGE. Purified protein was loaded onto 10-20% Tris-HCl gel. CL=unpurified cell lysate, GST-Tau=purified GST-Tau fusion protein, Tau441=purified Tau without GST tag.
Figure 2. Western blot of in vitro phosphorylated Tau-441 protein with human GSK-3β. Purified Tau-441 was incubated with human GSK-3β for 30 min. at 30°C. Phosphorylated Tau-441 (+GSK) and unphosphorylated Tau-441(-GSK) were resolved on 10-20% Tris gel and transferred onto nitrocellulose membrane. Proteins were probed with anti-Tau (393-411) and phosphospecific anti-Tau(pSer400) antibodies at 0.75µg/ml