Differential lipid specificities of the repeated domains of annexin IV

The roles of the four domains of annexin IV in binding to phospholipids and glycolipids were assessed by analyzing the binding of a group of mutant an nexins IV in which one or more of the four domains was inactivated by repla cing a critical amino residue(s) (Asp or Glu) with the neutral residue Ala. The data reveal that individual annexin domains may have characteristic af finities for different lipids. In particular, inactivation of the fourth do main inhibits the binding to phosphatidylserine (PS) and phosphatidylinosit ol (PI) but not to phosphatidylglycerol (PG), suggesting that this domain s pecifically can accommodate the larger head groups of PS and PI whereas the other three domains may form more restricted binding pockets. In order to block binding to PG, domain 1, or both domains 2 and 3 must be inactivated in addition to domain 4, suggesting that all four domains may be able to ac commodate the headgroup of PG to some extent. Binding to acidic glycolipids (sulfatides) was also sensitive to inactivation of domain 4. However, in t he case of sulfatides the nature of the binding reaction is fundamentally d ifferent compared with the binding to phospholipids since the interaction w ith sulfatides was highly sensitive to an increase in ionic strength. The b inding to sulfatides may depend therefore on charge-charge interactions whe reas the binding to phospholipid may involve a more specific interaction be tween the lipid headgroup and the protein surface, and/or interaction of th e protein with the hydrophobic portion of a lipid bilayer. (C) 2001 Elsevie r Science B.V. All rights reserved.