Coiled‐coil registry shifts in the F684I mutant of Bicaudal D result in cargo‐independent activation of dynein motility

Abstract

The dynein adaptor Drosophila Bicaudal D (BicD) is auto-inhibited and activates dynein motility only after cargo is bound, but the underlying mechanism is elusive. In contrast, we show that the full-length BicD/F684I mutant activates dynein processivity even in the absence of cargo. Our X-ray structure of the C-terminal domain of the BicD/F684I mutant reveals a coiled-coil registry shift; in the N-terminal region, the two helices of the homodimer are aligned, whereas they are vertically shifted in the wild-type. One chain is partially disordered and this structural flexibility is confirmed by computations, which reveal that the mutant transitions back and forth between the two registries. We propose that a coiled-coil registry shift upon cargo binding activates BicD for dynein recruitment. Moreover, the human homolog BicD2/F743I exhibits diminished binding of cargo adaptor Nup358, implying that a coiled-coil registry 10 shift may be a mechanism to modulate cargo selection for BicD2-dependent transport pathways.

Coil-to-Helix Transition at the Nup358-BicD2 Interface Activates BicD2 for Dynein Recruitment

“…A key step in activating dynein motility is the activation of BicD2 for dynein recruitment, and we and others have recently proposed that cargo-binding activates BicD2 for dynein recruitment by inducing a coiled-coil registry shift in BicD2 (i.e. a vertical displacement of the two α-helices against each other by one helical turn) 26,29,30,60 . In the absence of cargo, BicD2 forms an auto-inhibited looped dimer that cannot recruit dynein, with the CTD masking the Nterminal dynein/dynactin-binding site (NTD) [17][18][19][20][21][22][23][24][25][26][27]67 .…”

“…S8 and ref. 60 ). Based on these data, we estimate that the α-helical content increases by 14 ± 5 % upon Nup358/BicD2 complex formation, confirming a structural transition from random coil to α-helix.…”

“…CD spectroscopy was performed as previously described 60 . Purified proteins at a concentration of 0.3 mg/ml were dialyzed in the following buffer: 150 mM NaCl, 10 mM Tris pH 8 and 0.2 mM TCEP.…”

“…5b), which is a 12% change. We recently determined the experimental error to be ~5% ([Θ] = 2930 deg*cm 2 dmol -1 ) 60 , suggesting that the increase of the α-helical content in the complex is significant. We also estimated the number of residues that transition from random coil to α-helix upon complex formation, using a published thermal unfolding curve of the BicD2-CTD for calibration 30 (Fig.…”

A putative stem-loop structure in Drosophila crumbs is required for mRNA localisation in epithelia and germline cells

“…The lack of oocyte specification has also been observed upon loss of function of BicD (Dienstbier et al, 2009). Therefore, to determine the role of BicD in crb mRNA transport we used BicD 1 , which encodes a constitutively active protein, that binds to Dynein independent of the RNA cargo (Cui et al, 2020) and BicD 2 , shown to behave similar as BicD 1 (Larsen et al, 2008;Liu et al, 2013;Vazquez-Pianzola et al, 2014;Vazquez-Pianzola et al, 2017). crb mRNA in BicD 1 and BicD 2 heterozygous and BicD 1 /BicD 2 transheterozygous egg chambers appeared to be more tightly localised to the posterior end of the oocyte (Suppl.…”