Retrograde transport by the microtubule-associated protein MAP 1C

Abstract

Microtubules are involved in several forms of intracellular motility, including mitosis and organelle movement. Fast axonal transport is a highly ordered form of organelle motility that operates in both the anterograde (outwards from the cell body) and retrograde (from the periphery towards the cell body) direction¹. Similar microtubule-associated movement is observed in non-neuronal cells², and might be involved in secretion, endocytosis and the positioning of organelles within the cell^3,4. Kinesin⁵ is a mechanochemical protein that produces force along microtubules in an anterograde direction⁶. We recently found that the brain microtubule-associated protein MAP 1C (ref. 7) is a microtubule-activated ATPase⁸ and, like kinesin, can translocate microtubules in an in vitro assay for microtubule-associated motility⁸. MAP 1C seemed to be related to the ciliary and flagellar ATPase, dynein, which is thought to produce force in a direction opposite to that observed for kinesin⁹. Here we report that MAP 1C, in fact, acts in a direction opposite to kinesin, and has the properties of a retrograde translocator.