Dynein and dynactin leverage their bivalent character to form a high-affinity interaction

Dynein and dynactin are essential for retrograde transport and cell division, yet the specific interface and regulation of their interaction remain unclear. Prior research has identified the dynein intermediate chain (IC) and dynactin p150(Glued) as key players. However, the exact residues or mechanisms involved in their binding have not been fully characterized. This gap motivated investigations into the structural and functional details of the dynein-dynactin interface. No prior work had resolved the minimal binding regions or the conformational changes involved in their interaction. Existing models lacked clarity on how the interaction is modulated by environmental factors like salt or pH. This uncertainty drove the need for experimental validation of binding regions and the nature of the complex formed. The absence of structural data on the interface hindered progress in understanding how dynein and dynactin coordinate their functions. This study aimed to address these limitations through a combination of biochemical and biophysical methods.

This study aimed to identify the specific regions of dynein and dynactin that mediate their interaction. The researchers focused on the N-terminal region of the dynein intermediate chain (IC) and a segment of p150(Glued) from dynactin. Their goal was to determine if these regions are sufficient for binding and to characterize the nature of the interaction. The motivation stemmed from the lack of clarity about the interface and regulation of dynein-dynactin binding. By using monoclonal antibodies and alanine mutations, the team sought to validate the functional importance of these regions. The study also aimed to assess whether the interaction forms a stable complex and how it is influenced by environmental factors. The researchers proposed that the interaction involves a disorder-to-order transition. This approach allowed them to explore the structural and dynamic properties of the dynein-dynactin interface.

The researchers used multiple approaches to analyze the dynein-dynactin interaction. They mapped the binding region of the dynein intermediate chain to residues 10-44 using monoclonal antibodies. Yeast homologs were studied through double and triple alanine mutations in residues 6-19 of Pac11. Sedimentation equilibrium experiments were employed to determine the oligomeric state of the interaction. Circular dichroism (CD) experiments were used to assess the structural changes in the IC upon binding to p150(Glued). The binding affinity and stoichiometry of the complex were evaluated using sedimentation and CD techniques. The effect of salt, temperature, and pH on the interaction was tested to understand its stability. These methods provided insights into the structural and functional aspects of the dynein-dynactin interface.

The N-terminus of the mammalian dynein intermediate chain (residues 10-44) was shown to be sufficient for binding p150(Glued). Monoclonal antibodies that inhibit the dynein-dynactin interaction bind to this region of the IC. In yeast, mutations in residues 6-19 of the homolog Pac11 caused significant spindle positioning defects. A minimal fragment of p150(Glued), residues 381-530, was found to bind to the dynein IC. Sedimentation equilibrium experiments revealed that the IC and p150(Glued) fragments form a 2:2 complex. This tetrameric complex is sensitive to salt, temperature, and pH, indicating electrostatic interactions dominate the binding. Circular dichroism experiments showed that the N-terminus of the IC is disordered and becomes ordered upon binding p150(Glued). These findings suggest the dynein-dynactin interaction involves a disorder-to-order transition.

The data suggest that the dynein-dynactin interaction involves a disorder-to-order transition at the interface. The interaction is mediated by the N-terminus of the dynein intermediate chain and a segment of p150(Glued). The binding is sensitive to environmental factors like salt, temperature, and pH. The formation of a 2:2 complex indicates a stable but reversible interaction. The structural changes observed in the IC upon binding suggest a dynamic interface. The use of monoclonal antibodies and alanine mutations validated the functional importance of the identified regions. These findings provide insights into the mechanism of dynein-dynactin binding. The results support the idea that the interaction leverages a bivalent-bivalent character for high-affinity binding.