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Original Article |
Correspondence to: Sandra Citi, Department of Molecular Biology, University of Geneva, 30 Quai Ernest Ansermet, 1211 Geneva 4, Switzerland. Tel:41-22-7026182 Fax:41-22-7026868
We characterized the sequence and protein interactions of cingulin, an Mr 140160-kD phosphoprotein localized on the cytoplasmic surface of epithelial tight junctions (TJ). The derived amino acid sequence of a full-length Xenopus laevis cingulin cDNA shows globular head (residues 1439) and tail (1,3261,368) domains and a central
-helical rod domain (4401,325). Sequence analysis, electron microscopy, and pull-down assays indicate that the cingulin rod is responsible for the formation of coiled-coil parallel dimers, which can further aggregate through intermolecular interactions. Pull-down assays from epithelial, insect cell, and reticulocyte lysates show that an NH2-terminal fragment of cingulin (1378) interacts in vitro with ZO-1 (Kd ~5 nM), ZO-2, ZO-3, myosin, and AF-6, but not with symplekin, and a COOH-terminal fragment (3771,368) interacts with myosin and ZO-3. ZO-1 and ZO-2 immunoprecipitates contain cingulin, suggesting in vivo interactions. Full-length cingulin, but not NH2-terminal and COOH-terminal fragments, colocalizes with endogenous cingulin in transfected MDCK cells, indicating that sequences within both head and rod domains are required for TJ localization. We propose that cingulin is a functionally important component of TJ, linking the submembrane plaque domain of TJ to the actomyosin cytoskeleton.
Key Words: cingulin, tight junction, epithelia, MDCK, protein
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