Biology subjects

Mabuchi, T.

Publications and source records attributed to Mabuchi, T..

6 recordsLinked to original sources

bioRxiv2026

N-terminal intrinsically disordered region mediates self-catalytic interfacial nucleation of Aspergillus oryzae hydrophobin RolA

Hydrophobins are biosurfactant proteins that coat the cell surfaces of filamentous fungi. On the conidial surface, hydrophobins self-assemble into rodlets, forming a dense hydrophobic film that promotes air-dispersibility. Although rodlet formation is closely associated with the physiology of filamentous fungi, its underlying molecular mechanisms remain largely unknown. Previously, we revealed that RolA, a hydrophobin derived from Aspergillus oryzae, forms rodlets at the air-water interface. In this study, we focused on the flexible N-terminal region of RolA, which lacks a well-defined tertiary structure, and hypothesized that this intrinsically disordered region regulates rodlet formation. To investigate its role, we used RolA mutants with reduced charges in the N-terminal region and analyzed the rodlet formation process on the surface of a water-in-air sessile droplet using atomic force microscopy. In addition, we quantitatively characterized rodlet formation at the air-water interface by applying a kinetic perspective to the interfacial tension change profiles obtained from dynamic surface tension measurements. The results suggested that RolA first forms a monolayer at the air-water interface, then rodlet formation proceeds through the continuous supply of free RolA monomers from the bulk phase to the interfacial RolA film. Our molecular dynamics simulations of RolA at the interface supported a model in which RolA molecules within the interfacial film interact with free monomers in the bulk phase through their N-terminal regions. These results reveal a previously unidentified role of the N-terminal region in rodlet formation and provide a more comprehensive framework for understanding the molecular mechanism underlying RolA rodlet formation.

biophysics↗

bioRxiv2025

Human Interleukin-4-Dependent Facilitation of Human IgG Production in PBL-NOG-hIL-4-Tg mice

Immune-humanized mice provide valuable experimental models for evaluating immune-based therapies, yet the induction of human antigen-specific IgG production remains limited due to species-specific incompatibilities. Our previous work demonstrated that NOG-hIL-4-Tg mice, which express human interleukin-4 (IL-4), support human T and B cell maintenance and enable antigen-specific IgG production following transplantation of human peripheral blood mononuclear cells (PBMCs). In this study, we investigated how IL-4 enhances antibody responses in this model. Flow cytometry and histological analysis revealed that human B cell maintenance was associated with specific plasma hIL-4 concentration ranges at supraphysiological levels. T and B cell receptor repertoire analysis using next-generation sequencing showed that clonal diversity remained largely conserved for one month and decreased to three months post-engraftment. Immunoglobulin repertoire profiling confirmed IgG class switching in an IL-4-concentration-dependent manner. Among the IgG subclasses, IgG3 increased during the first and second months and then decreased thereafter. In contrast, IgG1 tended to increase over time; however, the proportion of IgG subclass varied among individual donors. Following immunization with two distinct peptide antigens, the mice produced enhanced levels of antigen-reactive IgG. However, many B cell clones also exhibited weak responses to unrelated third-party antigens, likely reflecting insufficient affinity maturation. Histological evaluation showed tertiary lymphoid structure (TLS)-like accumulations of B and T cells in the spleen, although fully developed germinal centers were absent. Taken together, these findings demonstrate that NOG-hIL-4-Tg mice maintain human B cells within a regulated IL-4 environment, promote early formation of splenic tertiary lymphoid structures, and support IgG production characterized by clonal expansion, class switching, and somatic hypermutation. These results confirm that human IL-4 expression supports human antibody responses in the PBL-NOG-hIL-4-Tg mouse system. (278)

immunology↗

bioRxiv2024

Conserved loop of a phase modifier endows protein condensates with fluidity

Dipeptide repeats (DPRs) that are gene products from abnormal hexanucleotide repeat expansion in C9orf72 trigger amyotrophic lateral sclerosis (ALS) through unknown mechanism. This study highlights, importin Karyopherin{beta}2 (Kap{beta}2), which is responsible for nuclear transport and phase modification of RNA-binding proteins (RBPs), as a major DPR target. We demonstrate DPR accumulation in the nucleus via Kap{beta}2-mediated transport, which results in dose-dependent toxicity observed in nematode and yeast models. In vitro interaction studies exploiting chemical probe arrays and biophysical measurements reveal multivalent DPR binding to Kap{beta}2, including at the conserved acidic loop. Refractive index and fluorescence imaging coupled with biochemical assays unveiled that binding of excess DPRs to the acidic loop turns a phase modifier Kap{beta}2 into phase disrupter, resulting more condensed and viscous RBP condensates. Our findings provides molecular insight into C9orf72-ALS related to age and repeat expansion.

biochemistry↗

bioRxiv2024

Facultative endosymbiosis between cellulolytic protists and methanogenic archaea in the gut of the Formosan termite Coptotermes formosanus

Anaerobic protists frequently harbour methanogenic archaea, which apparently contribute to the hosts fermentative metabolism by consuming excess H2. However, the ecological properties of endosymbiotic methanogens remain elusive in many cases. Here we investigated the ecology and genome of the endosymbiotic methanogen of the Cononympha protists in the hindgut of the termite Coptotermes formosanus. Microscopic and 16S rRNA amplicon sequencing analyses revealed that a single species, designated here Candidatus Methanobrevibacter cononymphae, is associated with both Cononympha leidyi and Cononympha koidzumii and that its infection rate in Cononympha cells varied from 0.0 to 99.8% among termite colonies. Fine-scale network analysis indicated that multiple 16S rRNA sequence variants coexisted within a single host cell and that identical variants were present in both Cononympha species and also on the gut wall. Thus, Ca. Methanobrevibacter cononymphae is a facultative endosymbiont, transmitted vertically with frequent exchanges with the gut environment. Indeed, transmission electron microscopy showed escape or uptake of methanogens from/by a Cononympha cell. The genome of Ca. Methanobrevibacter cononymphae showed features consistent with its facultative lifestyle: i.e., the genome size (2.7 Mbp) comparable to those of free-living relatives; the pseudogenization of the formate dehydrogenase gene fdhA, unnecessary within the non-formate-producing host cell; the dependence on abundant acetate in the host cell as an essential carbon source; and the presence of a catalase gene, required for colonization on the microoxic gut wall. Our study revealed a versatile endosymbiosis between the methanogen and protists, which may be a strategy responding to changing conditions in the termite gut.

microbiology↗

bioRxiv2023

Zinc finger domains bind low-complexity domain polymers

Self-association of low-complexity protein sequences (LC domains) is important for polymer formation. Several molecular chaperones are involved in the regulation of LC domain polymer formation. However, the mechanisms underlying cell recognition of LC domain polymers remain unclear. Here we show that zinc finger domains (ZnFs) bind LC domains of RNA-binding proteins in a cross-{beta} polymer-dependent manner. ZnFs bound to LC domain hydrogels and suppressed LC domain polymer formation. Moreover, ZnFs preferentially recognize LC domains in the polymeric state. These findings suggest that ZnFs act as physiological regulators of LC domain polymer formation.

biochemistry↗

bioRxiv2018

Alopecia areata susceptibility variant identified by MHC risk haplotype sequencing reproduces symptomatic patched hair loss in mice

BackgroundAlopecia areata (AA) is a highly heritable multifactorial and complex disease. However, no convincing susceptibility gene has yet been pinpointed in the major histocompatibility complex (MHC), a region in the human genome known to be associated with AA as compared to other regions.\n\nResultsBy sequencing MHC risk haplotypes, we identified a variant (rs142986308, p.Arg587Trp) in the coiled-coil alpha-helical rod protein 1 (CCHCR1) gene as the only non-synonymous variant in the AA risk haplotype. Using CRISPR/Cas9 for allele-specific genome editing, we then phenocopied AA symptomatic patched hair loss in mice engineered to carry the Cchcr1 risk allele. Skin biopsies of these alopecic mice showed strong up-regulation of hair-related genes, including hair keratin and keratin-associated proteins (KRTAPs). Using transcriptomics findings, we further identified CCHCR1 as a novel component of hair shafts and cuticles in areas where the engineered alopecic mice displayed fragile and impaired hair.\n\nConclusionsThese results suggest an alternative mechanism for the aetiology of AA based on aberrant keratinization, in addition to generally well-known autoimmune events.

genomics↗