We are also studying annexins, a family of proteins which interact with phospholipid bilayers in a Ca2+-dependent manner. Annexins have been reported to mediate membrane aggregation and fusion, as well as ion channel formation. Detailed structural studies of annexins are essential for understanding their fusogenic and ion channel forming properties at the atomic level. Annexin XII, isolated from Hydra vulgaris, was crystallized and its structure solved to 2.8 A. In its crystal form, it forms a homohexamer as described below.

The annexin XII hexamer, click to enlarge

 CPK model down the 3-fold axis, click to enlarge
Annexin XII hexamer viewed down the molecular 3-fold. The upper trimer is in red, the lower trimer in green. The type II Ca2+ sites are in blue, and the novel intermolecular Ca2+ sites in yellow. In the CPK space-filling model, note the central pore-like region.
Side view of the hexamer, click to enlarge CPK view down the 2-fold axis, click to enlarge

Ribbon and CPK models of the annexin XII hexamer viewed down the molecular 2-fold. Note that several of the type II Ca2+ (blue) remain accessible.

Initial model of hexamer:bilayer interaction and other possible annexin:bilayer interactions:
model 1:
model 2:
Crystal structure of the annexin XII hexamer and implications for bilayer insertion. Liecke H, Chang BT, Mailliard WS, Schlaepfer DD, Haigler HT (1995) Nature 378(6556):512-515 (abstract)

Annexin XII forms calcium-dependent multimers in solution and on phospholipid bilayers: a chemical cross-linking study. Mailliard WS, Luecke H, Haigler HT (1997) Biochemistry 36(29): 9045-9050 (abstract)
This page created 8/8/98 by JP, last modified 2/25/2000