Crystal structure of porcine cathepsin H determined at 2.1 A resolution: location of the mini-chain C-terminal carboxyl group defines cathepsin H aminopeptidase function

Structure. 1998 Jan 15;6(1):51-61. doi: 10.1016/s0969-2126(98)00007-0.

Abstract

Background: Cathepsin H is a lysosomal cysteine protease, involved in intracellular protein degradation. It is the only known mono-aminopeptidase in the papain-like family and is reported to be involved in tumor metastasis. The cathepsin H structure was determined in order to investigate the structural basis for its aminopeptidase activity and thus to provide the basis for structure-based design of synthetic inhibitors.

Results: The crystal structure of native porcine cathepsin H was determined at 2.1 A resolution. The structure has the typical papain-family fold. The so-called mini-chain, the octapeptide EPQNCSAT, is attached via a disulfide bond to the body of the enzyme and bound in a narrowed active-site cleft, in the substrate-binding direction. The mini-chain fills the region that in related enzymes comprises the non-primed substrate-binding sites from S2 backwards.

Conclusions: The crystal structure of cathepsin H reveals that the mini-chain has a definitive role in substrate recognition and that carbohydrate residues attached to the body of the enzyme are involved in positioning the mini-chain in the active-site cleft. Modeling of a substrate into the active-site cleft suggests that the negatively charged carboxyl group of the C terminus of the mini-chain acts as an anchor for the positively charged N-terminal amino group of a substrate. The observed displacements of the residues within the active-site cleft from their equivalent positions in the papain-like endopeptidases suggest that they form the structural basis for the positioning of both the mini-chain and the substrate, resulting in exopeptidase activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Aminopeptidases / chemistry*
  • Animals
  • Binding Sites / physiology
  • Cathepsin B / chemistry
  • Cathepsin H
  • Cathepsins / chemistry*
  • Crystallography, X-Ray
  • Cysteine Endopeptidases / chemistry*
  • Cysteine Proteinase Inhibitors / metabolism
  • Glycosylation
  • Lysosomes / enzymology
  • Models, Molecular
  • Molecular Sequence Data
  • Oligosaccharides / chemistry
  • Protein Precursors / chemistry
  • Protein Processing, Post-Translational / physiology
  • Protein Structure, Secondary
  • Sequence Alignment
  • Swine

Substances

  • Cysteine Proteinase Inhibitors
  • Oligosaccharides
  • Protein Precursors
  • Cathepsins
  • Aminopeptidases
  • Cysteine Endopeptidases
  • Cathepsin B
  • Cathepsin H