Biochemical characterization and structural modeling of human cathepsin E variant 2 in comparison to the wild-type protein

Biol Chem. 2012 Mar;393(3):177-86. doi: 10.1515/hsz-2011-0219.


Cathepsin E splice variant 2 appears in a number of gastric carcinomas. Here we report detecting this variant in HeLa cells using polyclonal antibodies and biotinylated inhibitor pepstatin A. An overexpression of GFP fusion proteins of cathepsin E and its splice variant within HEK-293T cells was performed to show their localization. Their distribution under a fluorescence microscope showed that they are colocalized. We also expressed variants 1 and 2 of cathepsins E, with propeptide and without it, in Escherichia coli. After refolding from the inclusion bodies, the enzymatic activity and circular dichroism spectra of the splice variant 2 were compared to those of the wild-type mature active cathepsins E. While full-length cathepsin E variant 1 is activated at acid pH, the splice variant remains inactive. In contrast to the active cathepsin E, the splice variant 2 predominantly assumes β-sheet structure, prone to oligomerization, at least under in vitro conditions, as shown by atomic force microscopy as shallow disk-like particles. A comparative structure model of splice variant 2 was computed based on its alignment to the known structure of cathepsin E intermediate (Protein Data Bank code 1TZS) and used to rationalize its conformational properties and loss of activity.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cathepsin E / chemistry*
  • Cathepsin E / genetics
  • Cathepsin E / metabolism
  • Escherichia coli / genetics
  • Gene Expression
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Microscopy, Atomic Force
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Isoforms / chemistry
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Sequence Alignment


  • Protein Isoforms
  • Recombinant Proteins
  • Cathepsin E