Lysine methylation is an endogenous post-translational modifications of tau protein in human brain and a modulator of aggregation propensity.

Tau protein undergoes a broad range of post-translational modifications in the brain, influencing its structure, solubility, and propensity to aggregate. This chapter presents an integrated methodological framework for characterizing tau methylation and evaluating its impact on tau biology. We describe procedures for isolating soluble and filamentous tau from post-mortem human brain tissue while preserving modifications for proteomic analysis. These approaches support precise mapping of methylation sites alongside other co-occurring modifications. To model methylation under controlled conditions, we outline protocols for recombinant tau expression, purification, and chemical reductive methylation, including radiolabeled assays for determining modification stoichiometry. We then detail biophysical assays used to assess how methylation alters tau conformation and aggregation propensity. This methodological framework supports experimentation seeking insight into mechanisms relevant to Alzheimer's disease and related tauopathies.