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| THE REFINED 2.15-A X-RAY CRYSTAL-STRUCTURE OF HUMAN LIVER CATHEPSIN-B - THE STRUCTURAL BASIS FOR ITS SPECIFICITY |
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| Author(s): MUSIL D, ZUCIC D, TURK D, ENGH RA, MAYR I, HUBER R, POPOVIC T, TURK V, TOWATARI T, KATUNUMA N, BODE W |
| Source: EMBO JOURNAL Volume: 10 Issue: 9 Pages: 2321-2330 Published: SEP 1991 |
| Times Cited: 354 References: 57 |
| Abstract: From the lysosomal cysteine proteinase cathepsin B, isolated from human liver in its two-chain form, monoclinic crystals were obtained which contain two molecules per asymmetric unit. The molecular structure was solved by a combination of Patterson search and heavy atom replacement methods (simultaneously with rat cathepsin B) and refined to a crystallographic R value of 0.164 using X-ray data to 2.15 angstrom resolution. The overall folding pattern of cathepsin B and the arrangement of the active site residues are similar to the related cysteine proteinases papain, actinidin and calotropin DI. 166 alpha-carbon atoms out of 248 defined cathepsin B residues are topologically equivalent (with an r.m.s. deviation of 1.04 angstrom) with alpha-carbon atoms of papain. However, several large insertion loops are accommodated on the molecular surface and modify its properties. The disulphide connectivities recently determined for bovine cathepsin B by chemical means were shown to be correct. Some of the primed subsites are occluded by a novel insertion loop, which seems to favour binding of peptide substrates with two residues carboxy-terminal to the scissile peptide bond; two histidine residues (His110 and His111) in this 'occluding loop' provide positively charged anchors for the C-terminal carboxylate group of such polypeptide substrates. These structural features explain the well-known dipeptidyl carboxypeptidase activity of cathepsin B. The other subsites adjacent to the reactive site Cys29 are relatively similar to papain; Glu245 in the S2 subsite favours basic P2-side chains. The above mentioned histidine residues, but also the buried Glu171 might represent the group with a pK(a) of approximately 5.5 near the active site, which governs endo- and exopeptidase activity. The 'occluding loop' does not allow cystatin-like protein inhibitors to bind to cathepsin B as they do to papain, consistent with the reduced affinity of these protein inhibitors for cathepsin B compared with the related plant enzymes. |
| Document Type: Article |
| Language: English |
| Reprint Address: MUSIL, D (reprint author), MAX PLANCK INST BIOCHEM, W-8033 MARTINSRIED, GERMANY |
Addresses:
1. JOZEF STEFAN INST, DEPT BIOCHEM, YU-61000 LJUBLJANA, YUGOSLAVIA
2. UNIV TOKUSHIMA, DEPT ENZYME CHEM, TOKUSHIMA 770, JAPAN
3. UNIV TOKUSHIMA, INST ENZYME RES, TOKUSHIMA 770, JAPAN |
| Publisher: OXFORD UNIV PRESS UNITED KINGDOM, WALTON ST JOURNALS DEPT, OXFORD, ENGLAND OX2 6DP |
| Subject Category: Biochemistry & Molecular Biology; Cell Biology |
| IDS Number: GB448 |
| ISSN: 0261-4189 |
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