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.
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.
Guncar
G
G
Department of Biochemistry and Molecular Biology, Jozef Stefan Institute, Ljubljana, Slovenia. gregor.guncar@ijs.si
Podobnik
M
M
Pungercar
J
J
Strukelj
B
B
Turk
V
V
Turk
D
D
D000595:Amino Acid Sequence; D000626:Aminopeptidases / Q000737:chemistry*; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002401:Cathepsin B / Q000737:chemistry; D056655:Cathepsin H; D002403:Cathepsins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003546:Cysteine Endopeptidases / Q000737:chemistry*; D015853:Cysteine Proteinase Inhibitors / Q000378:metabolism; D006031:Glycosylation; D008247:Lysosomes / Q000201:enzymology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry; D011498:Protein Precursors / Q000737:chemistry; D011499:Protein Processing, Post-Translational / Q000502:physiology; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D013552:Swine
D015853:Cysteine Proteinase Inhibitors; D009844:Oligosaccharides; D011498:Protein Precursors; D002403:Cathepsins; D000626:Aminopeptidases; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; D056655:Cathepsin H