A cryo-EM processing pipeline for microtubules using CryoSPARC.

Microtubules are cytoskeletal filaments that are typically characterized by a discontinuous helical lattice of α/β-tubulin heterodimers. Microtubules can also adopt variable lattice architectures both in vitro and in cellular contexts. Pseudo-helical averaging processing strategies have been developed to generate cryo-EM reconstructions of microtubules with and without decorating protein-binding partners, but these pipelines can be difficult to implement for the average user, especially for undecorated filaments. Here, we describe MiCSPARC, a cryo-EM processing pipeline developed around CryoSPARC [Punjani et al. (2017), Nat. Methods, 14, 290-296], which leverages automated particle picking and fast 3D refinement times in CryoSPARC to determine the structures of both decorated and undecorated microtubules. We generate reconstructions of undecorated GDP microtubules, as well as kinesin-1 motor domain-decorated GMPCPP filaments, at resolutions of up to 2.8 Å, demonstrating the robustness of the pipeline. Based on its convenient implementation and its ability to routinely generate high-resolution, seam-corrected microtubule reconstructions, MiCSPARC should provide a valuable tool for understanding microtubule dynamics, microtubule-associated proteins and microtubule-targeting agents.