Cryo-electron tomography of EB1-gold at growing microtubule ends
The structure of microtubule ends and the nucleotide state of tubulin are fundamental to microtubule dynamics. The end-binding protein EB1 tracks growing microtubule ends by recognizing GTP-tubulin dimers forming the terminal GTP-cap of microtubules. Here, we used EB1 conjugated to gold nanoparticles in combination with cryo-electron tomography to investigate the structure of the EB1-binding region of growing microtubule tips. We found that the EB1-binding sites are located on the outer surface of both open-curved and straight regions of tubulin sheets, and extend into closed regions of the microtubule lattice. Microtubules assembled in the presence of either GTP, GTP analogues or in cell extracts display similar, outwardly curved tubulin sheets, suggesting that they are curved independently of the nucleotide state of tubulin. Together, our results visualize the architecture of the GTP-cap at unprecedented resolution, and suggest a model that relates tubulin conformational changes to GTP-hydrolysis during microtubule assembly.