A. Blocker et al., MICROTUBULE-ASSOCIATED PROTEIN-DEPENDENT BINDING OF PHAGOSOMES TO MICROTUBULES, The Journal of biological chemistry, 271(7), 1996, pp. 3803-3811
In macrophages, phagosome movement is microtubule-dependent. Microtubu
les are a prerequisite for phagosome maturation because they facilitat
e interact-ions between phagosomes and organelles of the endocytic pat
hway. We have established an in vitro assay that measures the binding
of purified phagosomes to microtubules. This binding depends on the pr
esence of membrane proteins, most likely integral to the surface of ph
agosomes, and on macrophage cytosol. The cytosolic binding factor can
interact with microtubules prior to the addition of phagosomes to the
assay, suggesting that it is a microtubule-associated protein (MAP). C
onsistent with this, depletion of MAPs from the cytosol by microtubule
affinity removes all binding activity. Microtubule motor proteins sho
w no binding activity, whereas a crude MAP preparation is sufficient t
o support binding and to restore full binding activity to MAP-depleted
cytosol. We show that the activating MAP factor is a heat-sensitive p
rotein(s) that migrates at around 150 kDa by gel filtration.