Carbohydrate-binding proteins lectins, extracellular

Carbohydrates and carbohydrate-binding proteins, or lectins, are present on the cell surface and within the extracellular matrix, and their expressions are controlled both spatially and temporally during embryo development [1-3]. The cross-talk between glycosylated molecules and lectins is important for the harmonious embryo development, not only in cellular recognition phenomena but also as an intermediate in transduction of various signals depending on the developmental stage. 

The term selectin was introduced to describe three adhesion molecules whose function and expression were highly selective and which possessed a terminal lectin domain. The nomenclature for each molecule relates to the cell on which they were first described E-selectin (endothelium), L-selectin (lymphocyte), and P-selectin (platelet). All three share similar structural features (1) an extracellular amino terminal carbohydrate-binding (i.e., lectin-like) domain that requires Ca2+ for activation (2) an epidermal growth factor-like domain and (3) repeated domains with homologies to complement-regulatoiy proteins. 

These interactions involve adhesion proteins called selectins, which are found both on the rolling leukocytes and on the endothelial cells of the vascular walls. Selectins have a characteristic domain structure, consisting of an N-terminal extracellular lectin domain, a single epidermal growth factor (EGR) domain, a series of two to nine short consensus repeat (SCR) domains, a single transmembrane segment, and a short cytoplasmic domain. Lectin domains, first characterized in plants, bind carbohydrates... 

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