α-Catenin Can Form Asymmetric Homodimeric Complexes and/or Heterodimeric Complexes with β-Catenin*
- From the Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06510 and the ‡Department of Cell Biology and Anatomy, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
Abstract
The cadherin-based transmembrane cell-cell adhesive complex is thought to be composed of a cadherin molecule, a β-catenin, and an α-catenin, which connects the complex to the cytoskeleton. The precise stoichiometry of this complex remains uncertain. We have used a series of recombinant molecules and biophysical techniques to assess the multimeric state of human α- and β-catenin in vitro and then visualized them by electron microscopy after rotary shadowing. Calculated solution molecular masses are 213 kDa for α-catenin, 73 kDa for β-catenin, and 186 kDa for both. This suggests that α-catenin exists as a homodimer in solution, β-catenin is a monomer, and when both are present, they form α/β-catenin heterodimers. Co-precipitation and surface plasmon resonance assays localize the site of α-catenin dimerization to the NH2-terminal 228 amino acids. This region encompasses a high-affinity (K d = 100 nm) binding site for β-catenin that lies between residues 54 and 157. We anticipate that the oligomeric state of α-catenin and the relative stoichiometry of the components in the membrane adhesion complex will be dynamic and regulated by β-catenin, cell adhesion, and probably other factors as well.
Footnotes
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↵* This work was supported by a grant from the Patrick and Catherine Weldon Donaghue Medical Research Foundation (to D. L. R.), and by grants from the National Institutes of Health (to J. S. M. and Thomas D. Pollard (GM-26338)).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 Pathology, Yale University School of Medicine, 310 Cedar St., New Haven, CT 06510. Tel.: 203-737-4204; Fax: 203-737-5089; E-mail: david.rimm{at}yale.edu.
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↵1 Multiple forms of α-catenin exist representing both different gene products and alternative mRNA transcripts. The α-catenin used in this study is the common form found in epithelial cells, termed α1(E)-catenin (1). Here we use the general term “α-catenin” to refer to the α1(E)-catenin molecule except where otherwise indicated.
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↵2 The abbreviations used are: GST, glutathioneS-transferase; DTT, dithiothreitol; BSA, bovine serum albumin; PAGE, polyacrylamide gel electrophoresis; MES, 2-(N-morpholino)ethanesulfonic acid; R S, Stokes radius;
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- Received May 2, 1997.
- Revision received June 30, 1997.
