Role of coiled-coil registry shifts in activation of human Bicaudal D2 for dynein recruitment upon cargo-binding
Dynein adaptors such as Bicaudal D2 (BicD2) recognize cargo for dynein-dependent transport. BicD2-dependent transport pathways are important for brain and muscle development. Cargo-bound adaptors are required to activate dynein for processive transport, but the mechanism of action is elusive. Here, we report the structure of the cargo-binding domain of human BicD2 that forms a dimeric coiled-coil with homotypic registry, in which both helices are aligned. To investigate if BicD2 can switch to an asymmetric registry, where a portion of one helix is vertically shifted, we performed molecular dynamics simulations. Both registry types are stabilized by distinct conformations of F743. For the F743I variant, which increases dynein recruitment in the Drosophila homolog, and for the human R747C variant, which causes spinal muscular atrophy, spontaneous coiled-coil registry shifts are observed, which may cause the BicD2-hyperactivation phenotype and disease. We propose that a registry shift upon cargo-binding activates auto-inhibited BicD2 for dynein recruitment.\n\nHighlightsO_LIStable, bona fide BicD2 coiled-coils with distinct registries can be formed.\nC_LIO_LIWe provide evidence that a human disease mutation causes a coiled-coil registry shift.\nC_LIO_LIA coiled-coil registry shift could relieve BicD2-autoinhibition upon cargo-binding.\nC_LIO_LIThe ability to undergo registry shifts may be an inherent property of coiled-coils.\nC_LI\n\nIn BriefOur results support that stable coiled-coils of BicD2 with distinct registries can be formed, and suggest a molecular mechanism for such registry switches. We provide evidence that disease-causing mutations in coiled-coils may alter the equilibrium between registry-shifted conformers, which we propose as a general mechanism of pathogenesis for coiled-coils.\n\nGraphical Abstract O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY