Biology subjects

Fukai, S.

Publications and source records attributed to Fukai, S..

4 recordsLinked to original sources

bioRxiv2026

The vacuolar tauopathy-associated mutation D395G confers redox sensitivity to p97/VCP

The multifunctional AAA+ ATPase p97/VCP is a pivotal regulator of cellular proteostasis, extracting polyubiquitinated substrates from protein complexes or organelle membranes for proteasomal degradation. Mutations in p97 are linked to a broad spectrum of neurodegenerative disorders, including multisystem proteinopathy and amyotrophic lateral sclerosis. Here, we provide insights into the basis of dysfunction in p97D395G, implicated in vacuolar tauopathy, using an integrated structural approach. The mutation destabilizes the interaction network in the transient ADP.Pi state previously identified in p97WT and alters the dynamics of the linker between the tandem ATPase domains, resulting in decreased ATPase activity. We further demonstrate that the D395G mutation sensitizes p97 to oxidative stress by enhancing C522 oxidation, thereby perturbing nucleotide binding in D2, and define the functional basis of this oxidative inactivation of p97. These findings reveal redox control as a key regulatory layer of the p97 ATPase cycle and provide a mechanistic framework for how oxidative stress contributes to p97-associated neurodegeneration.

molecular biology↗

bioRxiv2025

Structural basis for the folding of PINK1 by the HSP90-CDC37 chaperone complex

PTEN-induced kinase 1 (PINK1) is a mitochondrial serine/threonine kinase that plays a central role in Parkin-dependent mitophagy. Mutations in PINK1 are associated with familial Parkinsons disease. PINK1 is a high-affinity client of the HSP90-CDC37 complex and is stabilized by this chaperone system. However, the molecular mechanism by which HSP90-CDC37 facilitates the folding of PINK1 remains unclear. Here, we present a cryogenic electron microscopy structure of the human PINK1-HSP90-CDC37 complex. The {beta}5 strand of the PINK1 N-lobe is accommodated in the central channel of the HSP90 dimer, which holds the PINK1 kinase domain in a partially unfolded state. The C-lobe and unique C-terminal extension (CTE) of PINK1 is folded. HSP90 covers the CTE of PINK1, which overlaps with interaction sites for TOM5, TOM20, and the PINK1 N-helix. The HPNI motif of CDC37 interacts with the C-lobe of PINK1, mimicking the HPNI motif in the N-lobe. The pathogenic mutation L347P is suggested to disrupt these interactions, while H271Q is located within the HPNI motif in the N-lobe of PINK1. These findings provide structural insights into the folding of PINK1 and its dysfunction in Parkinsons disease.

molecular biology↗

bioRxiv2025

Structural insights into heterohexameric assembly of epilepsy-related ligand-receptor complex LGI1-ADAM22

Leucine-rich glioma-inactivated 1 protein (LGI1) is a secreted neuronal protein consisting of the N-terminal leucine-rich repeat (LRR) and C-terminal epitempin repeat (EPTP) domains. LGI1 is linked to epilepsy, a neurological disorder that can be caused by genetic mutations of genes regulating neuronal excitability (e.g., voltage- or ligand-gated ion channels). ADAM22 is a membrane receptor that binds to LGI1 extracellularly and interacts with AMPA-type glutamate receptors via PSD-95 intracellularly to maintain normal synaptic signal transmission. Structural analysis of the LGI1-ADAM22 complex is important for understanding the molecular mechanism of epileptogenesis and developing new therapies against epilepsy. We previously reported the crystal structure of a 2:2 complex consisting of two molecules of LGI1 and two molecules of the ADAM22 ectodomain (ECD), which is suggested to bridge neurons across the synaptic cleft. On the other hand, multiangle light scattering, small-angle X-ray scattering, and cryo-EM analyses have suggested the existence of a 3:3 complex consisting of three molecules of LGI1 and three molecules of ADAM22. In the previous cryo-EM analysis, many observed particles were in a dissociated state, making it difficult to determine the three-dimensional (3D) structure of the 3:3 complex. In this study, we stabilized the 3:3 LGI1-ADAM22ECD complex using chemical crosslinking and determined the cryo-EM structures of the LGI1LRR-LGI1EPTP- ADAM22ECD and 3:3 LGI1-ADAM22ECD complexes at 2.78 [A] and 3.79 [A] resolutions, respectively. Furthermore, high-speed atomic force microscopy (HS-AFM) visualized the structural features and flexibility of the 3:3 LGI1-ADAM22ECD complex in solution. We discuss new insights into the interaction modes of the LGI1-ADAM22 higher-order complex and the structural properties of the 3:3 LGI1-ADAM22 complex. SignificanceThe neuronal secretory protein Leucine-rich glioma-inactivated 1 (LGI1) and its receptor protein ADAM22 play a critical role in maintaining normal synaptic signal transmission. Genetic mutations in LGI1 are linked to epilepsy. Structural analysis of the LGI1-ADAM22 complex is crucial for understanding the molecular mechanisms of epileptogenesis and for developing targeted treatments. In this study, we determined the cryo-EM structure of the heterohexameric LGI1-ADAM22 complex and visualized the dynamics of this complex by high-speed atomic force microscopy.

biochemistry↗

bioRxiv2020

Neurexins play a crucial role in cerebellar granule cell survival by organizing autocrine machinery for neurotrophins

Neurexins (NRXNs) are among the key presynaptic cell adhesion molecules that regulate synapse function and formation via trans-synaptic interaction with postsynaptic ligands. Here, we generated cerebellar granule cell (CGC)-specific Nrxn triple-knockout (TKO) mice to allow the deletion of all NRXNs. Unexpectedly, most CGCs died in these mice. The requirement of NRNXs for cell survival was reproduced in cultured CGCs. We showed that the axons of cultured Nrxn TKO CGCs that were not in contact with the postsynaptic structure had defects in the formation of presynaptic protein cluster and action potential-induced Ca2+ influx. Additionally, these cells were impaired in the secretion from axons of depolarization-induced fluorescence-tagged brain-derived neurotrophic factor (BDNF), and the cell-survival defect was rescued by the application of BDNF. Our results suggest that CGC survival is maintained by autocrine neurotrophic factors, and that NRXNs organize the presynaptic protein clusters and the autocrine neurotrophic factor secretory machinery independent of contact with postsynaptic ligands.

neuroscience↗