Structure
Volume 6, Issue 1, 15 January 1998, Pages 51-61
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Research Article
Crystal structure of porcine cathepsin H determined at 2.1 å resolution: location of the mini-chain C-terminal carboxyl group defines cathepsin H aminopeptidase function

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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 å 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 substratebinding 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.

Keywords

aminopeptidase
cathepsin H
crystal structure
cysteine protease
papain

Cited by (0)

G Gunčar, M Podobnik, J Pungerčar, B Štrukelj, V Turk and D Turk, Department of Biochemistry and Molecular Biology, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.

E-mail address for G Gunčar (corresponding author): [email protected].