Actin-induced dimerization of palladin promotes actin-bundling

Click on the DOI link to access the article (may not be free).A subset of actin binding proteins is able to form crosslinks between two or more actin filaments, thus producing structures of parallel or networked bundles. These actin crosslinking proteins interact with actin through either bivalent binding or dimerization. We recently identified two binding sites within the actin binding domain of palladin, an actin crosslinking protein that plays an important role in normal cell adhesion and motility during wound healing and embryonic development. In this study, we show that actin induces dimerization of palladin. Furthermore, the extent of dimerization reflects earlier comparisons of actin binding and bundling between different domains of palladin. On the basis of these results we hypothesized that actin binding may promote a conformational change that results in dimerization of palladin, which in turn may drive the crosslinking of actin filaments. The proximal distance between two actin binding sites on crosslinking proteins determines the ultrastructural properties of the filament network, therefore we also explored interdomain interactions using a combination of chemical crosslinking experiments and actin cosedimentation assays. Limited proteolysis data reveals that palladin is less susceptible to enzyme digestion after actin binding. Our results suggest that domain movements in palladin are necessary for interactions with actin and are induced by interactions with actin filaments. Accordingly, we put forth a model linking the structural changes to functional dynamics.Start-up funds from Wichita State University and a Center of Biomedical Research Excellence (COBRE) grant from the National Center for Research Resources; Grant number: 5P20RR017708; Grant sponsor: The National Institute of General Medical Sciences; Grant number: 8P20GM103420; Grant sponsor: Institutional Development Award (IDeA) from the National Institute of General Medical Sciences from the National Institutes of Health; Grant number: P20GM103418