Microtubules are polar cylindrical structures of linear protofilaments consisting of tubulin heterodimers. Microtubule ends undergo continuous assembly and disassembly powered by guanosine triphosphate (GTP) hydrolysis. The rapidly growing microtubule plus ends interact with many proteins, collectively known as plus-end tracking proteins (+TIPs). Among +TIPs, the end-binding (EB) proteins contact the growing microtubule end directly, to mediate further +TIP–microtubule interactions. Despite having been extensively studied, how EBs associate with microtubule ends has remained a long-standing question.

Maurer et al. elucidate the structural basis of the EB–microtubule interaction by employing cryo-electron microscopy, subnanometre single particle reconstruction and fluorescence microscopy (Cell 13, 371–382; 2012). They show that Mal3, the fission yeast EB, binds microtubule protofilaments by contacting four tubulin dimers. Their data indicate that the proximity of EB to the GTP-binding site of tubulin allows it to interact with the growing microtubule end by sensing conformational changes resulting from the microtubule nucleotide state. The authors further demonstrate that EB binding to the microtubule end forms a stabilizing zone that protects microtubules from depolymerization. These findings link EB function to microtubule-end stability and underscore the importance of EBs in forming a structural and functional hub at microtubule ends that supports recruitment of further factors to the microtubule plus end.