Actin-cross-linking proteins assemble actin filaments into higher-order structures essential for orchestrating cell shape, adhesion, and motility. Missense mutations in the tandem calponin homology domains of their actin-binding domains (ABDs) underlie numerous genetic diseases, but a molecular understanding of these pathologies is hampered by the lack of high-resolution structures of any actin-cross-linking protein bound to F-actin. Here, taking advantage of a high-affinity, disease-associated mutant of the human filamin A (FLNa) ABD, we combine cryo-electron microscopy and functional studies to reveal at near-atomic resolution how the first calponin homology domain (CH1) and residues immediately N-terminal to it engage actin. We further show that reorientation of CH2 relative to CH1 is required to avoid clashes with actin and to expose F-actin-binding residues on CH1. Our data explain localization of disease-associated loss-of-function mutations to FLNaCH1 and gain-of-function mutations to the regulatory FLNaCH2. Sequence conservation argues that this provides a general model for ABD–F-actin binding.
- cryoelectron microscope
Iwamoto, D. V., Huehn, A., Simon, B., Huet-Calderwood, C., Baldassarre, M., Sindelar, C. V., & Calderwood, D. A. (2018). Structural basis of the filamin A actin-binding domain interaction with F-actin. Nature Structural & Molecular Biology, 25, 918-927. https://doi.org/10.1038/s41594-018-0128-3