Human Cathepsin O2, a Matrix Protein-degrading Cysteine Protease Expressed in Osteoclasts

doi:10.1074/jbc.271.4.2126

Human Cathepsin O2, a Matrix Protein-degrading Cysteine Protease Expressed in Osteoclasts

FUNCTIONAL EXPRESSION OF HUMAN CATHEPSIN O2 IN SPODOPTERA FRUGIPERDA AND CHARACTERIZATION OF THE ENZYME (*)

From the From Khepri Pharmaceuticals, Inc., South San Francisco, California 94080

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Abstract

Cathepsin O2, a human cysteine protease predominantly present in osteoclasts, has been functionally expressed in Spodoptera frugiperda Sf9 cells using the Autographa californica nuclear polyhedrosis virus. Following in vitro activation at pH 4.0 with pepsin, active enzyme with an apparent molecular weight of 29,000 was obtained. N-terminal sequencing revealed the typical processing site for cysteine proteases of the papain family with a proline in the position adjacent to the N-terminal alanine residue. The SP subsite specificity of human cathepsin O2 is similar to cathepsin S but distinguished from cathepsins L and B. Similar to cathepsin S, cathepsin O2 is characterized by a bell-shaped pH activity profile and is stable at pH 6.5 for 30 min at 37°C. Cathepsin O2 is further distinguished by its potent collagenolytic activity against Type I collagen between pH 5 and 6, and elastinolytic activity against insoluble elastin at pH 7.0.

Its capacity to efficiently degrade Type I collagen and its high expression in osteoclasts suggest that cathepsin O2 may play a major role in human osteoclastic bone resorption.

Footnotes

↵*The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

Z-

benzyloxycarbonyl

-MCA

4-methyl-7-coumarylamide

E-64

L-3-carboxy-trans-2,3-epoxypropionyl-leucylamido-(4-guanidino)butane

CHN

diazomethane.
↵²D. Brömme and M. McGrath, unpublished results.
↵³D. Brömme, unpublished results.
↵⁴A. Rinne and D. Brömme, unpublished data.
- Received July 27, 1995.
- Revision received November 2, 1995.