The Nucleotide-Binding State of Microtubules Modulates Kinesin Processivity and Tau's Ability to Inhibit Kinesin Mediated Transport

Abstract

Tau's ability to act as a potent inhibitor of kinesin motility in vitro suggests it may actively participate in the regulation of axonal transport in vivo. However, it remains unclear how kinesin based transport could then proceed effectively in neurons, where tau is expressed at high levels. One potential explanation is that tau, a conformationally dynamic protein, has multiple modes of interaction with the microtubule, not all of which are inhibitory for kinesin motility. Thus, if tau can bind microtubules in distinct conformations or at unique binding sites that no longer inhibit kinesin, transport would proceed unhindered along the axon. Previous studies support the hypothesis that tau has at least two modes of interaction with microtubules, but the mechanisms by which tau adopts these different conformations and their functional consequences have not previously been investigated. In the present study we have used single molecule imaging techniques to demonstrate that tau inhibits kinesin motility in an isoform dependent manner on GDP microtubules stabilized with either paclitaxel or glycerol, but not GMPCPP-stabilized microtubules. Furthermore, the order of tau addition to microtubules before or after polymerization has no effect on tau's ability to modulate kinesin motility regardless of the stabilizing agent used. Finally, the processive run length of kinesin is reduced on GMPCPP microtubules relative to GDP-microtubules. These results shed new light on tau's potential role in the regulation of axonal transport, which is more complex than previously recognized.