Solution Structure of a Syndecan-4 Cytoplasmic Domain and Its Interaction with Phosphatidylinositol 4,5-Bisphosphate*
- From the ‡Department of Biochemistry, College of Science, Yonsei University, Seoul 120-740, Korea and the§Department of Cell Biology and the Cell Adhesion & Matrix Research Center, University of Alabama at Birmingham, Birmingham, Alabama 35294
Abstract
Syndecan-4, a transmembrane heparan sulfate proteoglycan, is a coreceptor with integrins in cell adhesion. It has been suggested to form a ternary signaling complex with protein kinase Cα and phosphatidylinositol 4,5-bisphosphate (PIP2). Syndecans each have a unique, central, and variable (V) region in their cytoplasmic domains, and that of syndecan-4 is critical to its interaction with protein kinase C and PIP2. Two oligopeptides corresponding to the variable region (4V) and whole domain (4L) of syndecan-4 cytoplasmic domain were synthesized for nuclear magnetic resonance (NMR) studies. Data from NMR and circular dichroism indicate that the cytoplasmic domain undergoes a conformational transition and forms a symmetric dimer in the presence of phospholipid activator PIP2. The solution conformations of both free and PIP2-complexed 4V have been determined by two-dimensional NMR spectroscopy and dynamical simulated annealing calculations. The 4V peptide in the presence of PIP2 formed a compact dimer with two twisted strands packed parallel to each other and the exposed surface of the dimer consisted of highly charged and polar residues. The overall three-dimensional structure in solution exhibits a twisted clamp shape having a cavity in the center of dimeric interface. In addition, it has been observed that the syndecan-4V strongly interacts not only with fatty acyl groups but also the anionic head group of PIP2. These findings reveal that PIP2 promotes oligomerization of syndecan-4 cytoplasmic domain for transmembrane signaling and cell-matrix adhesion.
Footnotes
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↵* This work was supported by a grant from Yonsei University Research Fund of 1997 (to W. T. L.) and by National Institutes of Health Grant GM50194 (to J. R. C.).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: Dept. of Biochemistry, College of Science, Yonsei University, Seodaemoon-Gu, Shinchon-dong, Seoul 120-740, Korea. Tel: 82-2-361-2706; Fax: 82-2-362-9897; E-mail: wlee{at}nestis.yonsei.ac.kr.
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↵1 The abbreviations used are: V, variable; C, constant; PIP2, phosphatidylinositol 4,5-bisphosphate; PKC, protein kinase C; NOESY, nuclear Overhauser effect spectroscopy; NOE, nuclear Overhauser effect; TOCSY, total correlation spectroscopy; DQF, double quantum filtered; COSY, correlated spectroscopy; SA, simulated annealing; cPKC, classical PKC.
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- Received January 15, 1998.
- Revision received February 11, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
