Many prescriptions of traditional medicines (TMs), whose efficacy has been tested in clinical practice, have great therapeutic value and represent an excellent resource for drug discovery. Research into single compounds of TMs, such as artemisinin from Artemisia annua L., has achieved great success; however, it has become evident that a TM prescription (which frequently contains various herbs or other components) has a synergistic effect in effecting a cure or reducing toxicity. Network pharmacology targets biological networks and analyzes the links among drugs, targets, and diseases in those networks. Comprehensive, systematic research into network pharmacology is consistent with the perspective of holisticity, which is a main characteristic of many TMs. By means of network pharmacology, research has demonstrated that many a TM show a synergistic effect by acting at different levels on multiple targets and pathways. This approach effectively bridges the gap between modern medicine and TM, and it greatly facilitates studies into the synergistic actions of TMs. There are different kinds of synergistic effects with TMs, such as synergy among herbs, effective parts, and pure compounds; however, for various reasons, new drug discovery should at present focus on synergy among pure compounds.

Dynein adaptors such as Bicaudal D2 (BicD2) recognize cargo for dynein-dependent transport, and cargo-bound adaptors are required to activate dynein for processive transport, but the mechanism of action is unknown. Here we report the X-ray structure of the cargo-binding domain of human BicD2 and investigate the structural dynamics of the coiled-coil. Our molecular dynamics simulations support the fact that BicD2 can switch from a homotypic coiled-coil registry, in which both helices of the homodimer are aligned, to an asymmetric registry, where a portion of one helix is vertically shifted, as both states are similarly stable and defined by distinct conformations of F743. The F743I variant increases dynein recruitment in the Drosophila homologue, whereas the human R747C variant causes spinal muscular atrophy. We report spontaneous registry shifts for both variants, which may be the cause for BicD2 hyperactivation and disease. We propose that a registry shift upon cargo binding may activate autoinhibited BicD2 for dynein recruitment.

Dynein adaptor proteins such as Bicaudal D2 (BicD2) are integral components of the dynein transport machinery, as they recognize cargoes for cell cycle-specific transport and link them to the motor complex. Human BicD2 switches from selecting secretory and Golgi-derived vesicles for transport in G1 and S phase (by recognizing Rab6GTP), to selecting the nucleus for transport in G2 phase (by recognizing nuclear pore protein Nup358), but the molecular mechanisms governing this switch are elusive. Here, we have developed a quantitative model for BicD2/cargo interactions that integrates affinities, oligomeric states, and cellular concentrations of the reactants. BicD2 and cargo form predominantly 2:2 complexes. Furthermore, the affinity of BicD2 toward its cargo Nup358 is higher than that toward Rab6GTP. Based on our calculations, an estimated 1000 BicD2 molecules per cell would be recruited to the nucleus through Nup358 in the absence of regulation. Notably, RanGTP is a negative regulator of the Nup358/BicD2 interaction that weakens the affinity by a factor of 10 and may play a role in averting dynein recruitment to the nucleus outside of the G2 phase. However, our quantitative model predicts that an additional negative regulator remains to be identified. In the absence of negative regulation, the affinity of Nup358 would likely be sufficient to recruit BicD2 to the nucleus in G2 phase. Our quantitative model makes testable predictions of how cellular transport events are orchestrated. These transport processes are important for brain development, cell cycle control, signaling, and neurotransmission at synapses.

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.

Nup358 is a protein subunit of the nuclear pore complex that recruits the opposing microtubule motors kinesin-1 and dynein [via the dynein adaptor Bicaudal D2 (BicD2)] to the nuclear envelope. This pathway is important for positioning of the nucleus during the early steps of mitotic spindle assembly and also essential for an important process in brain development. It is unknown whether dynein and kinesin-1 interact with Nup358 simultaneously or whether they compete. Here, we have reconstituted and characterized a minimal complex of kinesin-1 light chain 2 (KLC2) and Nup358. The proteins interact through a W-acidic motif in Nup358, which is highly conserved among vertebrates but absent in insects. While Nup358 and KLC2 form predominantly monomers, their interaction results in the formation of 2:2 complexes, and the W-acidic motif is required for the oligomerization. In active motor complexes, BicD2 and KLC2 each form dimers. Notably, we show that the dynein adaptor BicD2 and KLC2 interact simultaneously with Nup358, resulting in the formation of 2:2:2 complexes. Mutation of the W-acidic motif results in the formation of 1:1:1 complexes. On the basis of our data, we propose that Nup358 recruits simultaneously one kinesin-1 motor and one dynein motor via BicD2 to the nucleus. We hypothesize that the binding sites are close enough to promote direct interactions between these motor recognition domains, which may be important for the regulation of the motility of these opposing motors. Our data provide important insights into a nuclear positioning pathway that is crucial for brain development and faithful chromosome segregation.