ABSTRACT
Breakdown of basement membranes is an important step in the controlled rearrangement of cells during metamorphosis, cell migration, and metastatic spread of tumor cells. One of our two laboratories found a unique collagenous peptide that only appears during metamor-phosis of Drosophila melanogaster. The other laboratory previously reported that during 20-hydroxyecdysone-induced eversion of Drosophila imaginal discs a glyco-protein named gp125 arises (Birr et al., 1990). We show that these two peptides are identical and that they are formed from basement membrane collagen IV. Cleav-age occurs at an imperfection of this homotrimeric col-lagen helix between residues 755/756 in the sequence CALDE/IKMPAK. The peptide is the carboxyl frag-ment, 100,647 Mr, as derived from the amino acid sequence of the collagen 1(IV) chain. The correspond-ing amino fragment was also recovered from a disul-fide-linked aggregate. This specific cleavage supports the concept of highly targeted, controlled breakdown of basement membranes during metamorphosis. Further-more, these cuts occur at strategic sites of the predicted supramolecular network of collagen IV molecules of Drosophila basement membranes.
