Differential functionality of microtubule binding motifs in the p150[Glued] subunit of dynactin

Dynactin is a multi-subunit protein complex that is the required cofactor for the cytoplasmic motor protein, dynein. Dynactin is critical for cytoplasmic activities such as vesicle transport, cytoskeletal organization, membrane organization and mitotic progression as it serves to increase processivity of dynein. The main subunit in focus for this study is the sidearm extension p150Glued. On the exposed end (N-terminus) lie two different microtubule binding motifs: CAP-Gly and Basic. CAP-Gly has a high binding affinity for microtubules, while Basic binds the microtubules quite weakly. It is at this location that dynactin is proposed to assist in the processivity of transporting cargo long distances in the cell, by providing additional support for the dynein molecule as it progresses along the microtubule. Analysis of the effects of overexpression of these motifs, alone or in tandem, suggested that there was no disruption of the dynein/dynactin interaction, but its ability to act in a processive manner had been perturbed. Effects on non-dynamic processes, such as Golgi localization and microtubule organization were generally weak, but effects were greater on y-tubulin organization. While this could suggest a defect in centrosome organization, we propose that it instead shows that cargo motility in the affected cells is defective, and that transport of centrosomal proteins to the centrosome is interrupted, suggesting a broader cargo-transport defect may be evident in these cells.