Kinesin-8-specific loop-2 controls the dual activities of the motor domain according to tubulin protofilament shape

Modified peptides and organic metabolites of cyanobacterial origin with antiplasmodial properties

As etiological agents of malaria disease, Plasmodium spp. parasites are responsible for one of the most severe global health problems occurring in tropical regions of the world. This work involved compiling marine cyanobacteria metabolites reported in the scientific literature that exhibit antiplasmodial activity. Out of the 111 compounds mined and 106 tested, two showed antiplasmodial activity at very low concentrations, with IC50 at 0.1 and 1.5 nM (peptides: dolastatin 10 and lyngbyabellin A, 1.9% of total tested). Examples of chemical derivatives generated from natural cyanobacterial compounds to enhance antiplasmodial activity and Plasmodium selectivity can be found in successful findings from nostocarboline, eudistomin, and carmaphycin derivatives, while bastimolide derivatives have not yet been found. Overall, 57% of the reviewed compounds are peptides with modified residues producing interesting active moieties, such as α- and β-epoxyketone in camaphycins. The remaining compounds belong to diverse chemical groups such as alkaloids, macrolides, polycyclic compounds, and halogenated compounds. The Dolastatin 10 and lyngbyabellin A, compounds with antiplasmodial high activity, are cytoskeletal disruptors with different protein targets.

Cryo-EM Unveils the Processivity Mechanism of Kinesin KIF1A and the Impact of its Pathogenic Variant P305L

Mutations in the microtubule-associated motor protein KIF1A lead to severe neurological conditions known as KIF1A-associated neurological disorders (KAND). Despite insights into its molecular mechanism, high-resolution structures of KIF1A-microtubule complexes remain undefined. Here, we present 2.7-3.4 Å resolution structures of dimeric microtubule-bound KIF1A, including the pathogenic P305L mutant, across various nucleotide states. Our structures reveal that KIF1A binds microtubules in one- and two-heads-bound configurations, with both heads exhibiting distinct conformations with tight inter-head connection. Notably, KIF1A's class-specific loop 12 (K-loop) forms electrostatic interactions with the C-terminal tails of both α- and β-tubulin. The P305L mutation does not disrupt these interactions but alters loop-12's conformation, impairing strong microtubule-binding. Structure-function analysis reveals the K-loop and head-head coordination as major determinants of KIF1A's superprocessive motility. Our findings advance the understanding of KIF1A's molecular mechanism and provide a basis for developing structure-guided therapeutics against KAND.

Nucleotide-free structures of KIF20A illuminate atypical mechanochemistry in this kinesin-6

KIF20A is a critical kinesin for cell division and a promising anti-cancer drug target. The mechanisms underlying its cellular roles remain elusive. Interestingly, unusual coupling between the nucleotide- and microtubule-binding sites of this kinesin-6 has been reported, but little is known about how its divergent sequence leads to atypical motility properties. We present here the first high-resolution structure of its motor domain that delineates the highly unusual structural features of this motor, including a long L6 insertion that integrates into the core of the motor domain and that drastically affects allostery and ATPase activity. Together with the high-resolution cryo-electron microscopy microtubule-bound KIF20A structure that reveals the microtubule-binding interface, we dissect the peculiarities of the KIF20A sequence that influence its mechanochemistry, leading to low motility compared to other kinesins. Structural and functional insights from the KIF20A pre-power stroke conformation highlight the role of extended insertions in shaping the motor's mechanochemical cycle. Essential for force production and processivity is the length of the neck linker in kinesins. We highlight here the role of the sequence preceding the neck linker in controlling its backward docking and show that a neck linker four times longer than that in kinesin-1 is required for the activity of this motor.

New insights into the mechanochemical coupling mechanism of kinesin-microtubule complexes from their high-resolution structures

Kinesin motor proteins couple mechanical movements in their motor domain to the binding and hydrolysis of ATP in their nucleotide-binding pocket. Forces produced through this 'mechanochemical' coupling are typically used to mobilize kinesin-mediated transport of cargos along microtubules or microtubule cytoskeleton remodeling. This review discusses the recent high-resolution structures (<4 Å) of kinesins bound to microtubules or tubulin complexes that have resolved outstanding questions about the basis of mechanochemical coupling, and how family-specific modifications of the motor domain can enable its use for motility and/or microtubule depolymerization.

Importin α/β promote Kif18B microtubule association and enhance microtubule destabilization activity

Tight regulation of microtubule (MT) dynamics is necessary for proper spindle assembly and chromosome segregation. The MT destabilizing Kinesin-8, Kif18B, controls astral MT dynamics and spindle positioning. Kif18B interacts with importin α/β as well as with the plus-tip tracking protein EB1, but how these associations modulate Kif18B is not known. We mapped the key binding sites on Kif18B, made residue-specific mutations, and assessed their impact on Kif18B function. Blocking EB1 interaction disrupted Kif18B MT plus-end accumulation and inhibited its ability to control MT length on monopolar spindles in cells. Blocking importin α/β interaction disrupted Kif18B localization without affecting aster size. In vitro, importin α/β increased Kif18B MT association by increasing the on-rate and decreasing the off-rate from MTs, which stimulated MT destabilization. In contrast, EB1 promoted MT destabilization without increasing lattice binding in vitro, which suggests that EB1 and importin α/β have distinct roles in the regulation of Kif18B-mediated MT destabilization. We propose that importin α/β spatially modulate Kif18B association with MTs to facilitate its MT destabilization activity. Our results suggest that Ran regulation is important not only to control molecular motor function near chromatin but also to provide a spatial control mechanism to modulate MT binding of nuclear localization signal-containing spindle assembly factors.

Mechanochemical tuning of a kinesin motor essential for malaria parasite transmission

Plasmodium species cause malaria and kill hundreds of thousands annually. The microtubule-based motor kinesin-8B is required for development of the flagellated Plasmodium male gamete, and its absence completely blocks parasite transmission. To understand the molecular basis of kinesin-8B's essential role, we characterised the in vitro properties of kinesin-8B motor domains from P. berghei and P. falciparum. Both motors drive ATP-dependent microtubule gliding, but also catalyse ATP-dependent microtubule depolymerisation. We determined these motors' microtubule-bound structures using cryo-electron microscopy, which showed very similar modes of microtubule interaction in which Plasmodium-distinct sequences at the microtubule-kinesin interface influence motor function. Intriguingly however, P. berghei kinesin-8B exhibits a non-canonical structural response to ATP analogue binding such that neck linker docking is not induced. Nevertheless, the neck linker region is required for motility and depolymerisation activities of these motors. These data suggest that the mechanochemistry of Plasmodium kinesin-8Bs is functionally tuned to support flagella formation.

Magic-angle-spinning NMR structure of the kinesin-1 motor domain assembled with microtubules reveals the elusive neck linker orientation

Microtubules (MTs) and their associated proteins play essential roles in maintaining cell structure, organelle transport, cell motility, and cell division. Two motors, kinesin and cytoplasmic dynein link the MT network to transported cargos using ATP for force generation. Here, we report an all-atom NMR structure of nucleotide-free kinesin-1 motor domain (apo-KIF5B) in complex with paclitaxel-stabilized microtubules using magic-angle-spinning (MAS) NMR spectroscopy. The structure reveals the position and orientation of the functionally important neck linker and how ADP induces structural and dynamic changes that ensue in the neck linker. These results demonstrate that the neck linker is in the undocked conformation and oriented in the direction opposite to the KIF5B movement. Chemical shift perturbations and intensity changes indicate that a significant portion of ADP-KIF5B is in the neck linker docked state. This study also highlights the unique capability of MAS NMR to provide atomic-level information on dynamic regions of biological assemblies.