High Resolution cryo-Em Structures of Dynactin'S Shoulder and Pointed End

Abstract

Dynactin is a 1.2 MDa complex that activates the molecular motor, dynein, for ultra-processive transport along microtubules. Dynactin consists of a cargo adaptor-binding filament whose length is defined by its flexible shoulder domain. Due to the lack of high-resolution information it is not known how the shoulder is organized to template dynactin's filament or which residues interact with cargo adaptors at the filament's pointed end. Here we combine multiple cryo-EM datasets and define precise masking strategies for particle signal subtraction and 3D classification. This overcomes domain flexibility and results in high resolution maps into which we can build the atomic structures of the shoulder and pointed end. The unique architecture of the shoulder is required to position the four identical p50 subunits in different conformations to bind dynactin's filament. The pointed end structure reveals, for the first time, the molecular basis for cargo adaptor binding.