Limited Cleavage of Extracellular Matrix Protein BM-40 by Matrix Metalloproteinases Increases Its Affinity for Collagens

doi:10.1074/jbc.272.14.9237

Limited Cleavage of Extracellular Matrix Protein BM-40 by Matrix Metalloproteinases Increases Its Affinity for Collagens*

From the ^‡ Max-Planck-Institut für Biochemie, D-82152 Martinsried, the
^§ Institute of Biochemistry II, Medical Faculty University of Cologne, D-50931 Köln, Federal Republic of Germany, the
^¶ Department of Crystallography, Birkbeck College, University of London, London WC1E 7HX, and the
^∥ Strangeways Research Laboratory, Cambridge CB1 4RN, Great Britain

** To whom correspondence should be addressed:
Max-Planck-Institut für Biochemie, Am Klopferspitz 18A, D-82152 Martinsried, Federal Republic of Germany
. Tel.: 49-089-8578-2440; Fax: 49-089-8578-2422.

Abstract

The 33-kDa matrix protein BM-40 (SPARC, osteonectin) consists of an acidic N-terminal domain I, a central cysteine-rich follistatin-like module, and a C-terminal extracellular calcium-binding (EC) module. Previous studies attributed collagen IV and high affinity calcium binding of BM-40 to its EC module, which was shown by x-ray crystallography to consist of an EF-hand pair surrounded by several α-helical and loop segments. This module was now shown by surface plasmon resonance assay to bind with similar affinities to collagens I, III, and V. Cleavage of recombinant BM-40 and its EC module by collagenase-3, gelatinases A and B, matrilysin, and stromelysin-1 showed similar fragment patterns, whereas collagenase-1 was inactive. Some differences were, however, observed in cleavage rates and the preference of certain cleavage sites. Edman degradation of fragments demonstrated only three to four major cleavage sites in the central region of domain I and a single uniform cleavage in helix C of the EC module. Cleavage is accompanied by a 7-20-fold increase in binding activity for collagens I, IV, and V but revealed only small effects on calcium-dependent α-helical changes in the EC module. The data were interpreted to indicate that helix C cleavage is mainly responsible for enhancing collagen affinity by exposing the underlying helix A of the EC module. A similar activation may also occur in situ as indicated previously for tissue-derived BM-40.

Footnotes

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

FS

follistatin

EC

extracellular calcium-binding

MMP

matrix metalloproteinases
↵²E. Kohfeldt, unpublished observations.
↵³P. Maurer, W. Göhring, R. Nischt, and R. Timpl, unpublished observations.
- Received November 22, 1996.