Adapter proteins help to control various aspects of cellular behaviour by mediating protein–protein interactions. Now, Kathrin Kirsch and colleagues report that two closely related adapter proteins – CMS and CIN85 – modulate dynamic rearrangements of the actin cytoskeleton (see p. 2366). Both proteins contain three N-terminal Src homology 3 (SH3) domains, a proline-rich region (PR), a linker region and a C-terminal coiled-coil (CC) domain that mediates oligomerization. The authors first show that CMS is a component of podosomes (actin-rich adhesion structures) and that its entire C-terminal half is required for efficient binding to filamentous actin. They then demonstrate that CMS and CIN85 both crosslink actin to form bundles; this activity depends on their PR and CC domains and is needed for cell migration. Finally, they show that CMS and CIN85 interact through their CC domains to form heterodimers. Because CIN85 exists as different isoforms, all of which contain the CC domain, the authors propose that heterotypic interactions between these isoforms and CMS regulate its binding to actin and thus modulate cytoskeletal rearrangements.