Reconstitution of Organelle Transport Along Microtubules In Vitro

In this chapter, we describe methods for reconstituting and analyzing the transport of isolated endogenous cargoes in vitro. Intracellular cargoes are transported along microtubules by teams of kinesin and dynein motors and their cargo-specific adaptor proteins. Observations from living cells show that organelles and vesicular cargoes exhibit diverse motility characteristics. Yet, our knowledge of the molecular mechanisms by which intracellular transport is regulated is not well understood. Here, we describe step-by-step protocols for the extraction of phagosomes from cells at different stages of maturation, and reconstitution of their motility along microtubules in vitro. Quantitative immunofluorescence and photobleaching techniques are also described to measure the number of motors and adaptor proteins on these isolated cargoes. In addition, we describe techniques for tracking the motility of isolated cargoes along microtubules using TIRF microscopy and quantitative force measurements using an optical trap. These methods enable us to study how the sets of motors and adaptors that drive the transport of endogenous cargoes regulate their trafficking in cells.