Biology subjects

Solmaz, S. R.

Publications and source records attributed to Solmaz, S. R..

5 recordsLinked to original sources

bioRxiv2026

Structural characterization of a minimal KLC2/Nup358/BicD2 complex

Cellular transport processes along microtubules are often facilitated by multi-motor complexes, which are connected by adapter proteins and cargoes. The nuclear pore protein Nup358, for example, interacts with the dynein adapter Bicaudal D2 (BicD2), which in turn recruits minus-end directed dynein motors and plus-end directed kinesin-1 motors for a nuclear positioning pathway that is essential for brain development. How motor recruitment is regulated by interactions of BicD2 with Nup358 is not well understood. Here, we characterize the structure of a minimal complex of kinesin-1 light chain 2 (KLC2), Nup358 and BicD2 by cryo-electron microscopy and small angle X-ray scattering. KLC2/Nup358 assumes a rod-like structure that increases in thickness, when BicD2 is bound. The addition of BicD2 also shifts the KLC2/Nup358/BicD2 complex towards a 2:2:2 stoichiometry, promoting dimerization at lower protein concentrations than without BicD2. Similarly, the presence of the Nup358/KLC2 interaction results in a shift towards a 2:2:2 stoichiometry. Based on these results, we hypothesize that KLC2 and BicD2 are recruited to Nup358 in a cooperative manner, and cooperativity may be promoted by modulation of the oligomeric state.

biochemistry↗

bioRxiv2025

Cargo recognition of Nesprin-2 by the dynein adapter Bicaudal D2 for a nuclear positioning pathway that is important for neuronal migration

Nesprin-2 and its paralog Nesprin-1 are subunits of LINC complexes that are essential for brain development. To position the nucleus for neuronal migration, Nesprin-2 interacts with the motors kinesin-1 and dynein, which are recruited by the adapter Bicaudal D2 (BicD2), but the molecular details of these interactions are elusive. Here, structural models of minimal Nesprin-2/BicD2 complexes with 1:2 and 2:2 stoichiometry were predicted using AlphaFold and experimentally validated by mutagenesis, binding assays and single-molecule biophysical studies. The core of the binding site is formed by spectrin repeats of Nesprin-2, which form an alpha-helical bundle with BicD2 that is structurally distinct from the Rab6/BicD2 and Nup358/BicD2 complexes. Such structural differences could fine tune motility of associated dynein and kinesin-1 motors for these transport pathways. Furthermore, the Nesprin-2 fragment interacts with full-length BicD2 and activates dynein/dynactin/BicD2 complexes for processive motility, suggesting that no additional components are required to reconstitute this transport pathway. Interestingly, either one or two Nesprin-2 molecules can bind to a BicD2 dimer and activate BicD2/dynein/dynactin complexes for processive motion, resulting in similar speed and run lengths. The BicD2/dynein-binding site is spatially close but does not overlap with the kinesin-1 recruitment site, thus both motors may interact with Nesprin-2 simultaneously. Several mutations of Nesprin-1 and 2 that cause Emery-Dreifuss muscular dystrophy are found in the motor-recruiting domain and may alter interactions with kinesin-1 and BicD2/dynein, consistent with the abnormally positioned nuclei found in patients with this disease.

biophysics↗

bioRxiv2021

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

Nup358, a nuclear pore protein, facilitates a nuclear positioning pathway that is essential for many biological processes, including neuromuscular and brain development. Nup358 binds and activates the auto-inhibited dynein adaptor Bicaudal D2 (BicD2), which in turn recruits and activates the dynein machinery to position the nucleus. However, the molecular details of the Nup358/BicD2 interaction remain poorly understood. Here, we show that a minimal Nup358 domain activates dynein/dynactin/BicD2 for processive motility on microtubules. Using nuclear magnetic resonance (NMR) titration and chemical exchange saturation transfer (CEST), a Nup358 helix encompassing residues 2162-2184 was identified, which transitioned from random coil to an -helix upon BicD2-binding and formed the core of the Nup358-BicD2 interface. Mutations in this region of Nup358 decreased the Nup358/BicD2 interaction, resulting in decreased dynein recruitment and impaired motility. BicD2 thus recognizes the cargo adaptor Nup358 though a "cargo recognition -helix", a structural feature that may stabilize BicD2 in its activated state and promote processive dynein motility.

biophysics↗

bioRxiv2019

Coiled-coil registry shifts in the F684I mutant of Bicaudal result in cargo-independent dynein recruitment

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 shift may be a mechanism to modulate cargo selection for BicD2-dependent transport pathways.

biophysics↗

bioRxiv2019

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

biophysics↗