New research utilized advanced imaging techniques to visualize the 3D structure of the dynein-dynactin complex bound to microtubules in mice for the first time. Within cells, dynein proteins have the job of transporting molecular cargo, such as organelles and cell signaling molecules, on top of microtubules. The findings were published in Nature Structural and Molecular Biology.
Malfunctioning dynein underlies some neurological disorders such as spinal muscular atrophy (SMA) and Charcot-Marie-Tooth (CMT) disease. A deeper understanding of the dynein-dynactin structure may help lead to better therapies for these disorders.
Image: These are the dynein-dynactin complex (multi-color) motors down a microtubule (green). The four motor domains are shown in yellow. Dynactin (blue) provides the scaffold to keep the two dyneins together. Courtesy of Danielle Grotjohn, Lander Lab.
Researchers understood that dynactin is a necessary tool for dynein to move cellular cargo but only had a partial understanding of how the two molecules interacted. The study used cryo-electron tomography (cryo-ET) to reconstruct a 3D image, or tomogram, of the dynein-dynactin complex. The team also developed advanced computational algorithms to improve the image quality and resolution of the components.
"We knew that dynein only becomes active when it binds with a partner called dynactin. The problem was that, historically, it was difficult to solve this structure because it is very flexible and dynamic," explains Danielle Grotjahn, a TSRI graduate student and co-first author of the study. "We needed to visualize these dynein-dynactin complexes to fundamentally understand how it works to transport molecules."
The 3D image revealed unexpectedly that the complex includes two dynein proteins instead of just one dynein molecule. In addition, since each dynein molecule has two motor domains, the complex has four motors in total.
"This discovery was totally unexpected, and will change how this motor complex is represented in cell biology and biochemistry text books," says Saikat Chowdhury, PhD, a TSRI research associate and co-first author of the study.
The image also clarified dynactin’s role in cellular transport. The research demonstrates that dynactin joins the two dynein molecules stabilizing them and promoting forward movement and increased processivity. Dynactin clearly appears to be essential in enabling dynein to successfully transport heavy cargo within a heavily trafficked cellular environment.