E. Bitto et Wh. Cho, ROLES OF INDIVIDUAL DOMAINS OF ANNEXIN-I IN ITS VESICLE BINDING AND VESICLE AGGREGATION - A COMPREHENSIVE MUTAGENESIS STUDY, Biochemistry, 37(28), 1998, pp. 10231-10237
TO understand the mechanism by which annexin I induces membrane aggreg
ation, a comprehensive mutagenesis of all six Ca2+-binding sites was p
erformed. When the cap residues of type II Ca2+-binding sites were sys
tematically mutated to Ala, a type II site in domain II was shown to b
e essential for Ca2+-dependent vesicle binding of annexin I. Domain II
was not, however, directly involved in vesicle aggregation. Instead,
type II sites in domains III and IV, respectively, and type III sites
in domains I and IV were involved in vesicle aggregation. When all typ
e II sites were deactivated, three type III sites provided residual ve
sicle binding and aggregating activities. Their contributions to these
activities in the presence of type II sites were, however, relatively
insignificant. To further investigate the role of each domain harbori
ng a type II site, a set of mutants containing only a specific type II
site(s) were generated and their activities measured. These measureme
nts again underscored the importance of domain II in vesicle binding o
f annexin I and the involvement of domains III and IV in vesicle aggre
gation. The roles of individual domains in vesicle binding and aggrega
tion can be accounted for by the conformational change of membrane-bou
nd annexin I involving modular rotation of domains (I/IV) following th
e initial membrane adsorption of domains (II/III). In conjunction with
mutagenesis studies on other annexins, these results show that indivi
dual domains of annexins, although structurally homologous, have disti
nct functions and that different annexins might interact with membrane
s via different domains.