Breakdown of basement membranes is an important step in the controlled
rearrangement of cells during metamorphosis, cell migration, and meta
static spread of tumor cells. One of our two laboratories found a uniq
ue collagenous peptide that only appears during metamorphosis of Droso
phila melanogaster. The other laboratory previously reported that duri
ng 20-hydroxyecdysone-induced eversion of Drosophila imaginal discs a
glycoprotein named gp125 arises (Birr et al., 1990). We show that thes
e two peptides are identical and that they are formed from basement me
mbrane collagen IV. Cleavage occurs at an imperfection of this homotri
meric collagen helix between residues 755/756 in the sequence CALDE/IK
MPAK. The peptide is the carboxyl fragment, 100,647 M(r), as derived f
rom the amino acid sequence of the collagen alpha1(IV) chain. The corr
esponding amino fragment was also recovered from a disulfide-linked ag
gregate. This specific cleavage supports the concept of highly targete
d, controlled breakdown of basement membranes during metamorphosis. Fu
rthermore, these cuts occur at strategic sites of the predicted supram
olecular network of collagen IV molecules of Drosophila basement membr
anes.