Alzheimer's β-secretase (BACE1), an aspartic protease, cleaves amyloid precursor protein to produce a neurotoxic peptide, amyloid-β, which plays a role in triggering Alzheimer's disease. We previously found that BACE1 also cleaves a glycosyltransferase, α2,6-sialyltransferase, as a physiological substrate. In the present study, we performed a BLAST homology search, identified two Drosophila aspartic proteases that are homologous to human BACE1, and isolated their cDNAs. The proteins encoded by the cDNAs were designated as DASP1 and DASP2, which exhibited 59% and 50% similarity to human BACE1, respectively. Each protein contained a pair of active site motifs (Asp/Thr or Ser/Gly), which is a common characteristic of aspartic proteases including BACE1. Although DASP1 and DASP2 did not contain an apparent transmenbrane domain, the proteases overexpressed in COS cells were localized in the Golgi area. Some of the DASP1 overexpressed in S2 cells was secreted, but none of the DASP2 was. DASP1 transcripts were expressed in the head of fruitflies, whereas DASP2 transcripts were mainly expressed in the body. When either DASP1 or DASP2 was coexpressed together with a Golgi-resident transferase, Drosophila heparan sulfate 6-O-sulfotransferase, the protease enhanced the secretion of the transferase from the cells, indicating that both DASP1 and DASP2 can induce the secretion of the 6-O-sulfotransferase.
Bibliographical noteFunding Information:
This work was supported in part by Frontier Research System Funds (Y.H.), Strategic Research Funds (Y.H.), and Industrial Collaboration Funds (Y.H.) from the RIKEN Institute, and Leading Project Funds and Grants-in-Aid for Scientific Research, Nos. 15631009 (Y.H.) and 15025273 (Y.H.), from the Ministry of Education, Science, Sports, and Culture of Japan. We wish to thank Dr. Karen J. Colley (University of Illinois, Chicago) for providing the rabbit anti–α2,6-sialyltransferase I polyclonal antibody. The secretarial assistance of Kazuko Hashimoto is also gratefully acknowledged.
- Aspartic protease
- Proteolytic cleavage