A newly discovered protein helps clean up cellular trash, Pankiv et al. show. The protein attaches cytoplasmic refuse collectors to cargo-hauling motors.
Autophagy allows cells to dispose of worn-out or damaged proteins and organelles. During the process, a membrane pouch called an autophagosome surrounds a portion of the cell's contents and ferries the material to the lysosome for digestion. Researchers suspect that autophagosomes travel to their destinations along microtubules, but how they move is uncertain. Pankiv et al. report that the previously undescribed protein FYCO1 connects to three key autophagy molecules and appears to couple autophagosomes to molecular motors.
The researchers identified the molecule because it latches onto LC3, a protein embedded in the surface of autophagosomes. But FYCO1 isn't faithful. It also sticks to the phospholipid PI3P, a component of the autophagosome membrane, and to the GTPase Rab7, which helps autophagosomes merge with lysosomes. The researchers surmise that FYCO1 and its partners form a trailer hitch that connects an autophagosome to a molecular motor.
When Pankiv et al. cranked up FYCO1 production in cells, they found that vesicles carrying Rab7 cruised toward the plus ends of microtubules and accumulated at the cell's edges. The direction of movement suggests that FYCO1 links to kinesin molecular motors. A separate connection would attach the autophagosome to dynein motors that tug in the opposite direction, allowing travel toward the other end of a microtubule.