Cut protein to boost fibers

In a new analysis of melanosome biogenesis, Berson et al. (page 521) demonstrate that the proteolytic cleavage of a glycoprotein drives the formation of the characteristic fibrous striations seen in these organelles. The work uncovers a general mechanism that may regulate the development of lysosome-related organelles in a variety of cell types, and also shows a striking parallel between the experimentally tractable melanocyte system and the complex pathogenesis of amyloid diseases.Melanosomes, specialized organelles that store melanin pigments, develop intralumenal fibrils superficially similar to those seen in amyloid diseases, but little is known about how these fibrils form. Previous work identified an apparent paradox, suggesting that the melanosome fibrils do not contain membrane, but do contain the integral membrane glycoprotein Pmel17.

The new work resolves...