Cytoplasmic Dynein Ring Tilting Detected by Combined polTIRF and Sub-Pixel Particle Tracking of Semiconductor Quantum Rods

Abstract

The~1.0 megadalton dynactin complex interacts with cytoplasmic dynein to increase its processivity during minus-end-directed transport of cargo along microtubules (MT). The detailed molecular understanding of how dynactin regulates dynein motility is still elusive due to lack of structural information of the complex. Here we present structure of vertebrate dynactin at 20Å resolution, achieved by negative stain electron microscopy (EM). The reconstruction reveals the overall architecture of dynactin, allowing for delineation of the major known subcomplexes of the molecule. We can clearly discern the individual Arp subunits arranged in actin like helical fashion in the filament, along with the capping density at the barbed-end, and the pointed-end complex. We can also identify the shoulder domain above the filament observing extensive interactions with the Arp subunits. Due to the flexibility of the extended p150Glued coiled-coil arm, whose base interacts with dynein and whose globular tip binds the MT surface, this region was not resolved in the 3D reconstruction. However, focused 2D analysis of the p150Glued arm revealed its attachment point at the shoulder domain, as well as structural details of the globular CAP-Gly domain. This structural study of the dynactin complex establishes a strong foundation for understanding how its architecture is adapted for concerted interaction with dynein, cargo, and MTs during transport processes.