Carbohydrate-Carbohydrate Recognition Promotes Cell Adhesion
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J12.4.1
Carbohydrate-carbohydrate recognition promotes cell adhesion Christine Gourier*, Eric Perez*, Yongmin Zhang†, Pierre Sinaÿ† * Laboratoire de Physique Statistique de l’Ecole Normale Supérieure, UMR 8550 associée au CNRS et aux universités Paris 6 et Paris 7. † Département de Chimie de l’Ecole Normale Supérieure, UMR 8642 associée au CNRS, 75231 Paris Cedex 05, France. ABSTRACT Recently, carbohydate-carbohydrate recognition has emerged as a new type of interaction in cell adhesion processes. One of these carbohydrates, the LewisX determinant (LeX), has been shown to be involved in murine embryogenesis. Here we confirm the existence of this specific interaction by measuring the adhesion between giant vesicles functionalised with synthetic Lex bearing lipids providing to the LeX determinent a high orientational freedom. This was obtained by micropipette aspiration and contact angle measurements. By using a simple model involving the several contributions to the adhesion free energy, specific and non specific interactions could be separated and quantified. In a second step, using natural Lex bearing sphingolipids, we could underscore the high sensitivity of LeX-LeX recognition to molecular structure and prove that the possible orientations provided by the natural LeX bearing molecules not only allow but strongly favor LeX-LeX recognition. INTRODUCTION Carbohydrate-carbohydrate interaction has recently emerged as an important type of interaction in cell adhesion [1]. One of these carbohydrates, the LewisX determinant (LeX) has been shown to be involved in murine embryogenesis. It is not expressed at the cell surface until the eight-cell stage, shows maximal expression at the 8-16 morula cells (i.e. compaction stage) and decline s rapidly after compaction. This compaction stage could be inhibited either by antiLex antibodies, Lex itself, or by inactivating the calcium with EDTA. These results led to the hypothesis of a calcium mediated Lex-Lex specific homotypic interaction as a basis for cell recognition [2]. The aim of this study was to confirm the existence of this calcium dependant homotypic LeX-LeX recognition [3-4] in a physicochemically well defined system and in conditions akin to the natural environment of the glycolipid, i.e. lipid bilayers in tight contact. This was done through the adhesion between two giant vesicles functionalised with synthetic glycolipids designed to provide the LeX determinants a high orientational mobility thought favourable for LeX-LeX recognition. An accurate quantitative analysis of the adhesion energies allowed us to separate non specific from specific LeX-LeX contributions, and to quantify them [4]. In cells, the LeX-bearing molecules are composed of a ceramide connected to the LeX trisaccharide through a lactose group. This geometry considerably restricts the possible orientations of the LeX [5] compared to the large freedom in orientation provided by the long flexible spacers of the neoglycolipids. It may therefore have a strong influence on the Lex-Lex recognition by inhib
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