Dystrophin binding to nonmuscle actin

We purified actin from bovine brain by DNase I affinity chromatography in order to compare the binding of dystrophin to muscle actin with its binding to nonmuscle actin. While both β- and γ-nonmuscle actins are expressed in brain, Western blot analysis with isoform-specific antibodies indicated that our purified brain actin was exclusively the γ-isoform. The recombinant amino-terminal, actin-binding domain of dystrophin bound to muscle and brain actin in a saturable manner (~ 1 mol/mol actin) with similar K(d) values of 13.7 ± 3.5 and 10.6 ± 3.7 μM, respectively. We further demonstrate that intact dystrophin in the dystrophin-glycoprotein complex bound with equal avidity to muscle and brain F-actin. These data argue that a preferential binding of dystrophin to nonmuscle actin is not the basis for its targeting to the muscle cell plasmalemma but do support the hypothesis that dystrophin is capable of interacting with filamentous actin in nonmuscle tissues.