Replacement of Threonine 558, a Critical Site of Phosphorylation of Moesinin Vivo, with Aspartate Activates F-actin Binding of Moesin
Journal of Biological Chemistry
Point and deletion mutants of moesin were examined for F-actin binding by blot overlay and co-sedimentation, and for intra-and intermolecular interactions with N-and C-terminal domains with yeast two-hybrid and in vitro binding assays. Wild-type moesin molecules interact poorly with F-actin and each other, and bind neither C-nor N-terminal fragments. Interaction with F-actin is strongly enhanced by replacement of Thr 558 with aspartate (T558D), by deletion of 11 N-terminal residues (DelN11), by
... sidues (DelN11), by deletion of the entire N-terminal membrane-binding domain of both wild type and T558D mutant molecules, and by exposure to phosphatidylinositol 4,5-diphosphate. Activation of F-actin binding is accompanied by changes in inter-and intramolecular domain interactions. The T558D mutation renders moesin capable of binding wild type but not mutated (T558D) Cterminal or wild type N-terminal fragments. The interaction between the latter two is prevented. DelN11 truncation enables binding of wild type N and C domain fragments. These changes suggest that the T558D mutation, mimicking phosphorylation of Thr 558 , promotes Factin binding by disruption of interdomain interactions between N and C domains and exposure of the high affinity F-actin binding site in the C-terminal domain. Oscillation between activated and resting state could thus provide the structural basis for transient interactions between moesin and the actin cytoskeleton in protruding and retracting microextensions.