Microtubule Structural State Recognition by End Binding Protein 1

Abstract

Microtubules are structural polymers that participate in a wide range of cellular functions and are the site of localization and activity for a host of proteins. End binding protein 1 (EB1) localizes primarily to GTP-bound tubulin subunits at the growing ends of microtubules, where it facilitates interactions with other key cellular proteins. However, reports of sublocalization of EB1 within the GTP-rich region at growing microtubule ends suggest that there may be an additional layer of regulation for EB1 binding to the microtubule. Using both bulk and sub-microtubule correlation TIRF microscopy experiments, we found that, independently of nucleotide state, EB1 exhibits preferential binding for non-lattice structures such as those found at microtubule ends or defects. To predict the mechanism for this preference, we performed 3D molecular diffusion simulations, and found that the unique binding location of EB1 at the pocket-like interface between four adjacent tubulin dimers results in a form of structural state recognition due to a high steric hindrance to binding within the lattice, which is reduced at microtubule ends or lattice defects. Additionally, our experiments and simulations using a tubulin face binding protein resulted in elimination of microtubule structure recognition, suggesting a general principle for protein association to cellular polymers based on the location and conformation of the binding interface.