The Notch receptor is a large, cell surface transmembrane protein involved in a wide variety of developmental processes in higher organisms []. It becomes activated when its extracellular region binds to ligands located on adjacent cells. Much of this extracellular region is composed of EGF-like repeats, many of which can be O-fucosylated. A number of these O-fucosylated repeats can in turn be further modified by the action of a beta-1,3-N-acetylglucosaminyltransferase enzyme known as Fringe []. Fringe potentiates the activation of Notch by Delta ligands, while inhibiting activation by Serrate/Jagged ligands. This regulation of Notch signalling by Fringe is important in many processes [].Four distinct Fringe proteins have so far been studied in detail; Drosophila Fringe (Dfng) and its three mammalian homologues Lunatic Fringe (Lfng), Radical Fringe (Rfng) and Manic Fringe (Mfng). Dfng, Lfng and Rfng have all been shown to play important roles in developmental processes within their host, though the phenotype of mutants can vary between species eg Rfng mutants are retarded in wing development in chickens, but have no obvious phenotype in mice [, , ]. Mfng mutants have not, so far, been charcterised. Biochemical studies indicate that the Fringe proteins are fucose-specific transferases requiring manganese for activity and utilising UDP-N-acetylglucosamine as a donor substrate []. The three mammalian proteins show distinct variations in their catalytic efficiencies with different substrates.
The Notch receptor is a large, cell surface transmembrane protein involved in a wide variety of developmental processes in higher organisms []. It becomes activated when its extracellular region binds to ligands located on adjacent cells. Much of this extracellular region is composed of EGF-like repeats, many of which can be O-fucosylated. A number of these O-fucosylated repeats can in turn be further modified by the action of a beta-1,3-N-acetylglucosaminyltransferase enzyme known as Fringe []. Fringe potentiates the activation of Notch by Delta ligands, while inhibiting activation by Serrate/Jagged ligands. This regulation of Notch signalling by Fringe is important in many processes [].Four distinct Fringe proteins have so far been studied in detail; Drosophila Fringe (Dfng) and its three mammalian homologues Lunatic Fringe (Lfng), Radical Fringe (Rfng) and Manic Fringe (Mfng). Dfng, Lfng and Rfng have all been shown to play important roles in developmental processes within their host, though the phenotype of mutants can vary between species e.g. Rfng mutants are retarded in wing development in chickens, but have no obvious phenotype in mice [, , ]. Mfng mutants have not, so far, been charcterised. Biochemical studies indicate that the Fringe proteins are fucose-specific transferases requiring manganese for activity and utilising UDP-N-acetylglucosamine as a donor substrate []. The three mammalian proteins show distinct variations in their catalytic efficiencies with different substrates.Dfng is a glucosaminyltransferase that controls the response of the Notch receptor to specific ligands which is localised to the Golgi apparatus [](not secreted as previously thought). Modification of Notch occurs through glycosylation by Dfng. This entry consists of Fringe proteins and related glycosyltransferase enzymes including:Beta-1,3-glucosyltransferase, which glucosylates O-linked fucosylglycan on thrombospondin type 1 repeat domains [].Core 1 beta1,3-galactosyltransferase 1, generates the core T antigen, which is a precursor for many extended O-glycans in glycoproteins and plays a central role in many processes, such as angiogenesis, thrombopoiesis and kidney homeostasis development [].
