| Type: | Family | Name: | Annexin, type X |
| Description: | The annexins (or lipocortins) are a family of proteins that bind to phospholipids in a calcium-dependent manner []. They are distributed ubiquitously in different tissues and cell types of higher and lower eukaryotes, including mammals, fish, birds, Drosophila melanogaster(Fruit fly), Xenopus laevis(African clawed frog), Caenorhabditis elegans, Dictyostelium discoideum(Slime mold) and Neurospora crassa[, ]. Annexins are absent from yeasts and prokaryotes []. The plant annexins are somewhat distinct from those found in other taxa [].Most eukaryotic species have 1-20 annexin (ANX) genes. All annexins share a core domain made up of four similar repeats, each approximately 70 amino acids long []. Each individual annexin repeat (sometimes referred to as endonexin folds) is folded into five alpha-helices, and in turn are wound into a right-handed super-helix; they usually contain a characteristic 'type 2' motif for binding calcium ions with the sequence 'GxGT-[38 residues]-D/E'. Animal and fungal annexins also have variable amino-terminal domains. The core domains of most vertebrate annexins have been analysed by X-ray crystallography, revealing conservation of their secondary and tertiary structures despite only 45-55% amino-acid identity among individual members. The four repeats pack into a structure that resembles a flattened disc, with a slightly convex surface on which the Ca 2+ -binding loops are located and a concave surface at which the amino and carboxyl termini come into close apposition.Annexins are traditionally thought of as calcium-dependent phospholipid-binding proteins, but recent work suggests a more complex set of functions. The famiy has been linked with inhibition of phospholipase activity, exocytosis and endoctyosis, signal transduction, organisation of the extracellular matrix, resistance to reactive oxygen species and DNA replication [].Human annexin A10 (annexin 14) was first identified in silico by searches of dbEST with a number of divergent annexins []. The analysis revealed singlehuman and mouse ESTs corresponding to a novel and rarely expressed annexin in which three of the four tetrad core repeats lack the calcium-binding domain. It was proposed that this subtype, together with A5 annexin, gave rise to the Type VI octad through a process of gene duplication and fusion in early chordate evolution []. | Short Name: | AnnexinX |
