The Membrane-spanning Proteoglycan NG2 Binds to Collagens V and VI through the Central Nonglobular Domain of Its Core Protein*
- From the ‡Burnham Institute, La Jolla Cancer Research Center, La Jolla, California 92037,§Institut de Biologie et Chimie des Proteines, 69367 Lyon Cedex 07 France, and¶Department of Neurosciences, The Cleveland Clinic Foundation, Cleveland, Ohio 44195
Abstract
NG2 is a membrane-spanning proteoglycan with a primary structure unique among cell surface or extracellular matrix proteins. To characterize the interaction between NG2 and extracellular matrix proteins, we have used a eukaryotic expression system to produce and purify several recombinant fragments covering not only the entire ectodomain of NG2 but also distinct subdomains of the molecule. Using a solid phase binding assay with various extracellular matrix proteins, we have identified two main ligands for NG2, namely, collagens V and VI. Consistent with previous models of glycosaminoglycan attachment, roughly 50% of the recombinant NG2 fragments containing the central domain have chondroitin sulfate chains attached to the protein core. These glycosaminoglycan chains are not directly involved in collagen binding, since chondroitinase-treated fragments exhibit an unimpaired ability to bind to both collagens. Using more restricted recombinant fragments of NG2, we mapped the binding site for both collagens to the central domain of NG2. Electron microscopy after rotary shadowing of native NG2 molecules indicates that this extended nonglobular domain provides a flexible connection joining the two N- and C-terminal globular regions of NG2. Rotary shadowing of mixtures of NG2 and collagen V or VI confirms a direct interaction between the molecules and indicates that the collagens align with the central region of NG2, giving the appearance of a rod between the N- and C-terminal globules.
Footnotes
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↵* This work was supported by National Institutes of Health Grant RO1NS21990.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.
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↵‖ To whom correspondence should be addressed: The Burnham Institute, La Jolla Cancer Research Center, 10901 North Torrey Pines Rd., La Jolla, CA 92037. Tel.: 619-455-6480; Fax: 619-646-3197; E-mail:stallcup{at}ljcrf.edu.
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↵1 The abbreviations used are: PCR, polymerase chain reaction; EC, extracellular; PAGE, polyacrylamide gel electrophoresis; P, peak; TBS, Tris-buffered saline; GAG, glycosaminoglycan.
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↵2 W. B. Stallcup, unpublished observations.
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- Received November 18, 1996.
- Revision received February 10, 1997.
