Study of Tau N-Terminal Mutation, R5L, on Tau Interaction with the Microtubule Lattice

Abstract

Understanding the physiological function of the intrinsically disordered microtubule associated protein (MAP) Tau has proven challenging. Tau, primarily expressed in neurons, is known to have a variety of axonal functions, including regulation of microtubule dynamics, modulation of kinesin motor motility, and participation in signaling cascades. Interestingly, research on the microtubule binding behavior of Tau reveals that Tau binds to the microtubule surface in a dynamic equilibrium between static and diffusive states. Although it is understood that the binding state equilibrium plays a role in physiological Tau function, such as modulation of kinesin motility, it is less understood how disease associated mutations affect Tau binding behavior and function. The canonical theory states that mutations in Tau reduce Tau affinity for the microtubule. Here, we investigate the role of an N-terminal disease associated mutation, R5L, in both the 3RS and 4RS Tau isoforms using an in vitro reconstituted system for single molecule Total Internal Reflection Fluorescence (smTIRF) Microscopy. Contrary to the canonical theory, we determined the R5L mutation does not reduce Tau affinity to the microtubule. This was seen across microtubule lattices and Tau isoforms. Currently, we are investigating the single molecule properties of microtubule bound R5L-Tau to better comprehend the consequence of the R5L mutation. Altogether, these results show the canonical theory of disease mechanism does not encompass all Tau mutations and the theory needs to be expanded. This work will inform the mechanisms by which N-terminal disease associated mutations alter Tau function.