Interaction of actin with the capping protein, CapZ from sea bass (Dicentrarchus labrax) white skeletal muscle

We have compared the functional properties of CapZ from fish white skeletal muscle with those of CapZ from chicken muscle. CapZ is a heterodimer, whic h enhances actin nucleation and inhibits the depolymerization process by bi nding to the barbed ends of microfilaments. Here, we report the interaction of CapZ not only with F-actin, but also with monomeric actin. The affinity of sea bass CapZ for G-actin estimated by enzyme-linked immunosorbent assa y (ELISA) was in the muM range. This association was PIP2 dependent. Bindin g contacts with the barbed end of actin were delimited by both ELISA and fl uorescence approaches. One site (actin sequence 338-348) was located in a h elical region of the subdomain 1, region already implicated in the interact ion with other actin binding proteins such as gelsolin. Another site implic ates the C-terminal region (sequence 360-372) of actin. Finally, the partia l competition of antibodies directed against CapZ alpha or beta -subunits t owards CapZ interaction with actin filaments suggests both subunits partici pate in the complex with actin. (C) 2000 Elsevier Science Inc. All rights r eserved.