Annexin

Annexins is the name of a family of proteins in eukaryotes, which have in common is the characteristic calcium- dependent binding to lipids in the cell membrane and to aggregate into trimers or hexamers. Hexamers then usually form ion channel - transport proteins. There are now over 100 annexins in 45 species sequenced, 12 of which in man. Other names lipocortin, Synexin or Endonexin.

A typical annexin protein is characterized by two important properties. Its polypeptide chain ( or eight in annexin VI) α -helical domains of similar structure folded in four repeated with a central hydrophobic core. The second characteristic is the formation of calcium -dependent binding to phospholipids, especially at acidic phospholipids having one or more negative charges.

The group of annexins is one of the two major calcium-binding proteins, additionally there is the group of Calmoduline.