MARK clears MAP-muddled traffic

Microtubule-associated proteins (MAPs) stabilize the filaments to which they are attached. But they are also a hindrance to microtubule-based motors trying to move themselves and their cargos down the tracks. Now, on page 99, Mandelkow et al. show that some kinases that phosphorylate MAPs in their microtubule-binding domains clear the path for motors. Alterations in the balance of this system may be an early defect in Alzheimer's disease.

Elevated levels of the neuronal MAP tau were previously shown to inhibit axon-directed transport. The group finds microtubule-based traffic is also inhibited by other MAPs, then tests what happens when MAPs are released from microtubules by phosphorylation.

One kinase that regulates this interaction is MARK, which phosphorylates tau, MAP2, and MAP4. Also known as Par-1, MARK is needed for...