Structural mechanisms of drebrin-mediated F-actin network modulation.

Drebrin modulates F-actin networks and links them to other intracellular components, regulating crucial processes including neuritogenesis, synaptic plasticity, virus internalisation and cancer invasion. Using single-particle cryo-EM we characterise drebrin's interaction with F-actin through two separate conserved actin binding domains (ABD1 and ABD2), revealing structural bases for its F-actin-modulating properties. We describe a multimodal interaction where drebrin's ABD1 can adopt two conformations and a long flexible loop connecting to ABD2 allows the two ABDs to occupy multiple relative positions along F-actin. The flexible loop connecting the two ABDs also confers some propensity to loosely bundle F-actin. Drebrin's ABDs bind across multiple actin protomers and their subdomains and modify the longitudinal inter-protomer interface, explaining its F-actin stabilising properties. Furthermore, we show drebrin's binding site on F-actin is shared with other critical actin-binding and regulatory proteins, explaining their competitive displacement.