Calcium modulates endopeptidase 24.15 (EC membrane association, secondary structure and substrate specificity

Vitor Oliveira, Paula A.G. Garrido, Claudia C. Rodrigues, Alison Colquhoun, Leandro M. Castro, Paulo C. Almeida, Claudio S. Shida, Maria A. Juliano, Luiz Juliano, Antonio C.M. Camargo, Stephen Hyslop, James L. Roberts, Valerie Grum-Tokars, Marc J. Glucksman, Emer S. Ferro

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


The metalloendopeptidase 24.15 (EP24.15) is ubiquitously present in the extracellular environment as a secreted protein. Outside the cell, this enzyme degrades several neuropeptides containing from 5 to 17 amino acids (e.g. gonadotropin releasing hormone, bradykinin, opioids and neurotensin). The constitutive secretion of EP24.15 from glioma C6 cells was demonstrated to be stimulated linearly by reduced concentrations of extracellular calcium. In the present report we demonstrate that extracellular calcium concentration has no effect on the total amount of the extracellular (cell associated + medium) enzyme. Indeed, immuno-cytochemical analyses by confocal and electron microscopy suggested that the absence of calcium favors the enzyme shedding from the plasma membrane into the medium. Two putative calcium-binding sites on EP24.15 (D93 and D159) were altered by site-directed mutagenesis to investigate their possible contribution to binding of the enzyme at the cell surface. These mutated recombinant proteins behave similarly to the wild-type enzyme regarding enzymatic activity, secondary structure, calcium sensitivity and immunoreactivity. However, immunocytochemical analyses by confocal microscopy consistently show a reduced ability of the D93A mutant to associate with the plasma membrane of glioma C6 cells when compared with the wild-type enzyme. These data and the model of the enzyme's structure as determined by X-ray diffraction suggest that D93 is located at the enzyme surface and is consistent with membrane association of EP24.15. Moreover, calcium was also observed to induce a major change in the EP24.15 cleavage site on distinctive fluorogenic substrates. These data suggest that calcium may be an important modulator of ep24.15 cell function.

Original languageEnglish (US)
Pages (from-to)2978-2992
Number of pages15
JournalFEBS Journal
Issue number12
StatePublished - Jun 2005


  • Calcium
  • Membrane binding
  • Peptide metabolism
  • Protease
  • Thimet oligopeptidase

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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