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.

The mRNA-bound proteome of the early fly embryo

“…Moreover, we identified BicD, a protein with noncanonical RBDs in the mRNA-bound proteome. BicD is a dynein adaptor protein anchoring the RNA-binding protein Egl (Dienstbier et al 2009) to dynein motors (Bullock and Ish-Horowicz 2001;Liu et al 2013). The enrichment of BicD in oligo(dT) precipitate suggests that the early fly mRBPome harbors previously uncharacterized RBPs directing transcript localization during early embryogenesis.…”

Bicaudal D Family Adaptor Proteins Control the Velocity of Dynein-Based Movements

“…Various members of the BICD protein family are very similar in structure: they are coiled coil proteins with a cargo-binding site located in the C terminus and motor-binding sites in the N-terminal half of the molecule (Hoogenraad et al, 2001(Hoogenraad et al, , 2003Liu et al, 2013;Schlager et al, 2010;Splinter et al, 2012). By comparing the amino acid sequences of Drosophila and mouse BICD family members, we found a highly conserved region in the N terminus of these proteins (Figures 2E and S3).…”

Mechanism and Regulation of Cytoplasmic Dynein

“…These include the GTP-bound conformation of Rab6/Rab6a, a GTPase that regulates the recruitment of kinesin and dynein to the Golgi complex, endoplasmic reticulum, and cytoplasm-derived vesicles (Coutelis & Ephrussi 2007; Hoogenraad et al 2001, 2003; Januschke et al 2007; Matanis et al 2002); the clathrin heavy chain, to facilitate endocytic processes (Li et al 2010); and the RNA-binding proteins Egalitarian and FMRP (Fragile X mental retardation protein), which allow mRNA to be transported by dynein (Bianco et al 2010, Liu et al 2013). …”