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Yoshiyuki Yasuda, Keiko Kohmura, Tomoko Kadowaki, Takayuki Tsukuba, Kenji Yamamoto

A new selective substrate for cathepsin E based on the cleavage site sequence of ?2-macroglobulin

Keywords: aspartic proteinase, ?2-macroglobulin, cathepsin E, selective substrate

Cathepsin E is an intracellular aspartic proteinase of the pepsin family predominantly expressed in cells of the immune system and believed to contribute to homeostasis by participating in host defense mechanisms. Studies on its enzymatic properties, however, have been limited by a lack of sensitive and selective substrates. For a better understanding of the importance of this enzyme in vivo, we designed and synthesized a highly sensitive peptide substrate for cathepsin E based on the sequence of the specific cleavage site of ?2-macroglobulin. The substrate constructed, MOCAc-Gly-Ser-Pro-Ala-Phe-Leu-Ala-Lys(Dnp)-D-Arg-NH₂[where MOCAc is (7-methoxycoumarin-4-yl)acetyl and Dnp is dinitrophenyl], derived from the cleavage site sequence of human ?2-macroglobulin, was the most sensitive and selective for cathepsin E, with k_cat/K_m values of 8–11 ?M^-1 S^-1, whereas it was resistant to hydrolysis by the analogous aspartic proteinases cathepsin D and pepsin, as well as the lysosomal cysteine proteinases cathepsins B, L, and H. The assay allows the detection of a few fmol of cathepsin E, even in the presence of plasma and cell lysate, and gives accurate results over a wide enzyme concentration range. This substrate might represent a useful tool for monitoring and accurately quantifying cathepsin E, even in crude enzyme preparations.

Biological Chemistry, Walter de Gruyter

Print ISSN: 1431-6730
Volume: 386, 03/2005
Pages: 299 - 305

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