Module 4: Figure annexin structure
Annexin structure and membrane association.
The annexins have four annexin repeats (lilac), which makes up the annexin core domain. Each repeat has a Ca2+-binding domain. Annexin A6 is unusual in that the core domain is duplicated, which has resulted from the fusion of annexins A5 and A10. When annexins bind Ca2+ (see A), a conformational change occurs to expose a hydrophobic concave surface that attaches to membranes through a salt bridge formed by Ca2+ interacting with the carbonyl and carboxy groups of the annexins and the negative charges on the phospholipid head groups in the membrane. The conformational change can also displace the N-terminal region (green) to open up the concave surface, which can then interact with other proteins such as actin. Annexin can also interact with S100A10 to form a symmetrical tetrameric structure capable of bringing together two membranes (see B).