A Complete Domain Structure ofDrosophilaTolloid Is Required for Cleavage of Short Gastrulation
Journal of Biological Chemistry
Drosophila tolloid (TLD) is a member of a family of proteinases that play important roles in development and includes mammalian tolloid (mTLD) and bone morphogenetic protein (BMP)-1. TLD accentuates the activity of decapentaplegic (DPP), a transforming growth factor ␤ superfamily growth factor, by cleaving its antagonist Short gastrulation (Sog). Similarly, the activity of BMP-2/4 (vertebrate homologues of DPP) is augmented by cleavage of chordin. However, whereas TLD is an effective Sogase,
... ffective Sogase, mTLD is a poor chordinase and is functionally replaced by its smaller splice variant BMP-1, which lacks the most C-terminal epidermal growth factor (EGF)-like and CUB domains of mTLD. Moreover, the minimal chordinase activity resides in the N-terminal half of BMP-1. This study showed that the proteolytic activity of TLD is considerably enhanced by Ca 2؉ and tested the hypothesis that the Sogase activity of TLD resides in the N-terminal half of the proteinase. Unexpectedly, it was found that TLD lacking the CUB4 and CUB5 domains and/or the EGF-like domains was unable to cleave Sog. Loss of function mutations have been reported in the tld gene that result in amino acid substitutions at E835K (in CUB4), S915L (in CUB5), and N760I (in EGF2) in TLD. The CUB mutants were found to be ineffective Sogases, but the activity of the EGF2 mutant was unchanged. The results show that substrate recognition and cleavage by Drosophila tolloid and mTLD are different despite their identical domain structure and homologous functions in patterning. The result that the N760I mutant has full Sogase activity suggests that novel substrates for TLD exist. . 2 The abbreviations used are: BMP-1, bone morphogenetic protein-1; TLD, Drosophila tolloid; mTLD, mammalian tolloid; EGF, epidermal growth factor; CUB domain, a protein domain first found in the complement components C1r/C1s, the sea urchin protein Uegf, and BMP-1; PSP, porcine sperm adhesion protein; HRP, horseradish peroxidase; Sog, Short gastrulation; DPP, decapentaplegic; Scw, Screw; MES, 4-morpholineethanesulfonic acid; MOPS, 4-morpholinepropanesulfonic acid; HA, epitope from the influenza A virus hemagglutinin.