Abstract
Annexins constitute an evolutionary conserved multigene protein superfamily characterized by their ability to interact with biological membranes in a calcium dependent manner. They are expressed by all living organisms with the exception of certain unicellular organisms. The vertebrate annexin core is composed of four (eight in annexin A6) homologous domains of around 70 amino acids, with the overall shape of a slightly bent ring surrounding a central hydrophilic pore. Calcium- and phospholipid-binding sites are located on the convex side while the N-terminus links domains I and IV on the concave side. The N-terminus region shows great variability in length and amino acid sequence and it greatly influences protein stability and specific functions of annexins. These proteins interact mainly with acidic phospholipids, such as phosphatidylserine, but differences are found regarding their affinity for lipids and calcium requirements for the interaction. Annexins are involved in a wide range of intra- and extracellular biological processes in vitro, most of them directly related with the conserved ability to bind to phospholipid bilayers: membrane trafficking, membrane-cytoskeleton anchorage, ion channel activity and regulation, as well as antiinflammatory and anticoagulant activities. However, the in vivo physiological functions of annexins are just beginning to be established.
Highlights
IntroductionAnnexins are a widely distributed multigene superfamily of structurally related calcium-dependent membrane-binding proteins that show a characteristic tetrad structure of homologous internal repeats
Annexins are a widely distributed multigene superfamily of structurally related calcium-dependent membrane-binding proteins that show a characteristic tetrad structure of homologous internal repeats.They are expressed in many organisms from protists to higher eukaryotes, including plants [1,2,3,4]
All the members of this family of proteins are structurally characterized by the presence of a highly conserved core composed of four homologous domains of about 70 amino acids showing a similar three-dimensional structure highly conserved throughout annexin evolution [6]
Summary
Annexins are a widely distributed multigene superfamily of structurally related calcium-dependent membrane-binding proteins that show a characteristic tetrad structure of homologous internal repeats. They are expressed in many organisms from protists to higher eukaryotes, including plants [1,2,3,4]. 1999, the nomenclature system for these proteins was accorded based on the molecular phylogeny and comparative genomic analysis [5] They are named “annexin” followed by a capital letter: A for human annexins and their cognate orthologs; B for other animal annexins, mainly invertebrate; C for Mycetozoa and fungi; D for plants; and E for Protista. We have focused on the structure and the interaction of annexins, mainly from the A subfamily, with phospholipid membranes, and the implication of these interactions on their cellular functions
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