Annexin-phospholipid interactions. Functional implications.
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.
Department of Biochemistry and Molecular Biology I, Faculty of Chemistry, Complutense University, Madrid 28040, Spain. turnay@bbm1.ucm.es.
María Antonia
MA
Lizarbe
Juan I
JI
Barrasa
Nieves
N
Olmo
Francisco
F
Gavilanes
Javier
J
Turnay