Microtubule-associated protein interactions with actin filaments: evidence for differential behavior of neuronal MAP-2 and tau in the presence of phosphatidyl-inositol.

Microtubule-associated protein (MAP) interactions with actin were investigated by falling-ball viscometry. At 1-2 microM MAP-2 or tau, we obtained a critical gelation concentration for actin of 0.1 mg/ml. In the presence of phosphatidyl-inositol, actin filament bundling was completely disrupted only when MAP-2 served as the cross-linker, whereas tau-induced bundling of actin was unaffected by phosphatidyl-inositol. This represents the first clear indication that MAP-2 and tau exhibit differential behavior in their interaction with cytoskeletal components.