Dumping of MVB cargo (green) into the vacuole (red) fails in mutants (right) that cannot oligomerize ESCRT-I.

Anew endosomal protein keeps ESCRT-I too wrapped up in itself to be attracted to anyone else, Chu et al. reveal on page 815. This matchbreaker prevents the premature assembly of the machinery that forms multivesicular bodies (MVBs).

MVBs are endosomes with internal vesicles. The vesicles contain membrane proteins bound for fusion with lysosomes or viral particles hoping to escape from the cell. Vesicles bud internally from the endosomal membrane with help from three ESCRT complexes (I, II, and III) that are sequentially recruited from the cytosol to the endosome. Chu et al. found a new component that helps keep this recruitment in proper order.

The helper is a small protein, which the authors call Mvb12, that binds to ESCRT-I and regulates its associations. With Mvb12, most ESCRT-I...

The Rockefeller University Press
2006
The Rockefeller University Press
2006
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