MICROTUBULE-ASSOCIATED PROTEIN MAP1A IS AN ACTIN-BINDING AND CROSS-LINKING PROTEIN

High molecular weight microtubule-associated proteins MAP1A and MAP2 f orm thin projections from microtubule surfaces and have been implicate d in crosslinking microtubules and other cytoskeletal components. We h ave purified native MAP1A from bovine brain and have studied its inter action with G- and F-actin. Using a solid-phase immunoassay we show th at MAP1A binds in a dose-dependent manner to both G-actin and F-actin. Addition of MAP1A to F-actin causes gelation of F-actin and SDS-PAGE analysis shows that MAP1A co-sediments with the gelled network, under conditions where F-actin alone does not pellet. The low apparent visco sity of F-actin is markedly increased in the presence of MAP1A, sugges ting that MAP1A can crosslink F-actin. Co-incubation experiments indic ate that MAP1A and MAP2 may bind to common or overlapping sites on the actin molecule. The widespread distribution of MAP1A and its interact ion with microtubules, actin, and intermediate filaments suggests that it may constitute an important determinant of neuronal and non-neuron al cellular morphology. (C) 1994 Wiley-Liss, Inc.