Mutual effects of alpha-actinin, calponin and filamin on actin binding

The mutual effect of three actin-binding proteins (alpha -actinin, calponin and filamin) on the binding to actin was analyzed by means of differential centrifugation and electron microscopy. In the absence of actin alpha -act inin, calponin and filamin do not interact with each other. Calponin and fi lamin do not interfere with each other in the binding to actin bundles. Sli ght interference was observed in the binding of alpha -actinin and calponin to actin bundles. Higher ability of calponin to depress alpha -actinin bin ding can be due to the higher stoichiometry calponin/actin in the complexes formed. The largest interference was observed in the pair filamin-alpha -a ctinin. These proteins interfere with each other in the binding to the bund led actin filaments; however, neither of them completely displaced another protein from its complexes with actin. The structure of actin bundles forme d in the presence of any one actin-binding protein was different from that observed in the presence of binary mixtures of two actin-binding proteins. In the case of calponin or its binary mixtures with alpha -actinin or filam in the total stoichiometry actin-binding protein/actin was larger than 0.5. This means that alpha -actinin, calponin and filamin may coexist on actin filaments and more than mol of any actin-binding protein is bound per two a ctin monomers. This may be important for formation of different elements of cytoskeleton. (C) 2001 Elsevier Science B.V. All rights reserved.