title: Bicaudal-D uses a parallel, homodimeric coiled coil with heterotypic registry to coordinate recruitment of cargos to dynein.
abstract: Cytoplasmic dynein is the major minus end-directed microtubule motor in eukaryotes. However, there is little structural insight into how different cargos are recognized and linked to the motor complex. Here we describe the 2.2 Å resolution crystal structure of a cargo-binding region of the dynein adaptor Bicaudal-D (BicD), which reveals a parallel coiled-coil homodimer. We identify a shared binding site for two cargo-associated proteins-Rab6 and the RNA-binding protein Egalitarian (Egl)-within a region of the BicD structure with classical, homotypic core packing. Structure-based mutagenesis in Drosophila provides evidence that occupancy of this site drives association of BicD with dynein, thereby coupling motor recruitment to cargo availability. The structure also contains a region in which, remarkably, the same residues in the polypeptide sequence have different heptad registry in each chain. In vitro and in vivo analysis of a classical Drosophila dominant mutation reveals that this heterotypic region regulates the recruitment of dynein to BicD. Our results support a model in which the heterotypic segment is part of a molecular switch that promotes release of BicD autoinhibition following cargo binding to the neighboring, homotypic coiled-coil region. Overall, our data reveal a pivotal role of a highly asymmetric coiled-coil domain in coordinating the assembly of cargo-motor complexes.
authors.affiliation: Division of Cell Biology, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Hannah K
authors.initials: HK
authors.lastname: Salter
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Holding
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Johnson
authors.forename: Elaine
authors.initials: E
authors.lastname: Stephens
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Lukavsky
authors.forename: John
authors.initials: J
authors.lastname: Walshaw
authors.forename: Simon L
authors.initials: SL
authors.lastname: Bullock
mesh_terms: D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D029721:Drosophila Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004398:Dyneins / Q000737:chemistry / Q000378:metabolism*; D005799:Genes, Dominant; D008954:Models, Biological; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D013329:Structure-Activity Relationship; D020691:rab GTP-Binding Proteins / Q000378:metabolism
chemical_list: C061998:BicD protein, Drosophila; D029721:Drosophila Proteins; C094135:Rab6 protein; C104613:egl protein, Drosophila; D004398:Dyneins; D020691:rab GTP-Binding Proteins
keywords: Bicaudal-D; Drosophila.; cargo binding; coiled coil; crystal structure; dynein