GTPgammaS microtubules mimic the growing microtubule end structure recognized by end-binding proteins (EBs).

Microtubule plus-end-tracking proteins (+TIPs) localize to growing microtubule plus ends to regulate a multitude of essential microtubule functions. End-binding proteins (EBs) form the core of this network by recognizing a distinct structural feature transiently existing in an extended region at growing microtubule ends and by recruiting other +TIPs to this region. The nature of the conformational difference allowing EBs to discriminate between tubulins in this region and other potential tubulin binding sites farther away from the microtubule end is unknown. By combining in vitro reconstitution, multicolor total internal reflection fluorescence microscopy, and electron microscopy, we demonstrate here that a closed microtubule B lattice with incorporated GTPγS, a slowly hydrolyzable GTP analog, can mimic the natural EB protein binding site. Our findings indicate that the guanine nucleotide γ-phosphate binding site is crucial for determining the affinity of EBs for lattice-incorporated tubulin. This defines the molecular mechanism by which EBs recognize growing microtubule ends.