Proceedings of the Japan Academy. Series B, Physical and Biological Sciences最新文献

Enhancing the thermostability of cellulose-degrading enzymes is pivotal for establishing an efficient bioconversion system from cellulosic materials to value-added compounds. Here, by introducing random and saturation mutagenesis into the Thermoascus aurantiacus β-glucosidase gene, we generated a hyperthermostable mutant with five amino acid substitutions. Analysis of temperature-induced unfolding revealed the involvement of each replacement in the increased T_m value. Structural analysis showed that all replacements are located at the periphery of the catalytic pocket. D433N replacement, which had a pronounced thermostabilizing effect (ΔT_m ＝ 4.5°C), introduced an additional hydrogen bond with a backbone carbonyl oxygen in a long loop structure. The mutant enzyme expressed in Kluyveromyces marxianus exhibited a T_m of 82°C and hydrolyzed cellobiose with k_cat and K_m values of 200 s^－1 and 1.8 mM, respectively. When combined with a thermostable endoglucanase, the mutant enzyme released 20％ more glucose than wild-type enzyme from cellulosic material. The mutant enzyme is therefore a noteworthy addition to the existing repertoire of thermostable β-glucosidases.

Thrombomodulin (TM) is an important regulator of intravascular blood coagulation, fibrinolysis, and inflammation. TM inhibits the procoagulant and proinflammatory activities of thrombin and promotes the thrombin-induced activation of protein C (PC) bound to the endothelial PC receptor (EPCR). Activated PC (APC) inactivates coagulation factors Va and VIIIa, thereby inhibiting blood clotting. APC bound to EPCR exerts anti-inflammatory and cytoprotective effects on vascular endothelial cells. TM promotes the activation of thrombin-activatable fibrinolysis inhibitor, and also protects cells in blood vessels from inflammation caused by pathogen-associated and damaged cell-associated molecules. Excessive anticoagulant, fibrinolytic, anti-inflammatory, and tissue regenerative effects in the TM-PC pathway are controlled by PC inhibitor. A recombinant TM drug (TM), a soluble form of natural TM developed from the cloned human TM gene, has been evaluated for efficacy in many clinical trials and approved as a treatment for disseminated intravascular coagulation (DIC) caused by diseases such as sepsis, solid tumors, hematopoietic tumors, and trauma. It is currently widely used to treat DIC in Japan.

This review outlines research on chemical biology using mainly microbial metabolites for agricultural applications. We established the RIKEN Natural Products Depository (NPDepo), housing many microbial metabolites, to support academic researchers who focus on drug discovery. We studied methods to stimulate secondary metabolism in microorganisms to collect various microbial products. The switch of secondary metabolism in microorganisms changes depending on the culture conditions. We discovered compounds that activate biosynthetic gene clusters in actinomycetes and filamentous fungi. Using these compounds, we succeeded in inducing the production of active compounds. Two approaches for screening bioactive compounds are described. One is phenotypic screening to explore antifungal compounds assisted by artificial intelligence (AI). AI can distinguish the morphological changes induced by antifungal compounds in filamentous fungi. The other is the chemical array method for detecting interactions between compounds and target proteins. Our chemical biology approach yielded many new compounds as fungicide candidates.

The formation of autophagosomes is a pivotal step in autophagy, a lysosomal degradation system that plays a crucial role in maintaining cellular homeostasis. After autophagy induction, phase separation of the autophagy-related (Atg) 1 complex occurs, facilitating the gathering of Atg proteins and organizes the autophagosome formation site, where the initial isolation membrane (IM)/phagophore is generated. The IM then expands after receiving phospholipids from endomembranes such as the endoplasmic reticulum. This process is driven by the collaboration of lipid transfer (Atg2) and scrambling (Atg9) proteins. The IM assumes a cup shaped morphology and undergoes closure, resulting in the formation of a double membrane-bound autophagosome. The Atg8 lipidation system is hypothesized to be a pivotal factor in this process. This review presents an overview of the current understanding of these processes and discusses the basic mechanisms of autophagosome formation.

It is now accepted that the pathogenesis of type 2 diabetes in East Asians including Japanese differs distinctly from that in Caucasians. Many non-obese individuals in Japan develop type 2 diabetes and present clinically with insufficient insulin secretion rather than a large increase in the insulin resistance. To understand the pathophysiology of this non-obese diabetes, we studied Goto-Kakizaki rats, a unique model of spontaneous non-obese diabetes, and identified mitochondrial dysfunction in pancreatic β-cells as a factor in decreased insulin secretion. Looking for a clinical treatment option, we focused on the incretins because of their glucose-dependent insulin stimulatory effect. Our findings have contributed to the understanding of incretin action and the development of incretin-associated therapeutics and shed light on the nature of East Asian diabetes and its optimal clinical treatment.

Herein, the first English article demonstrating the Yagi-Uda antenna is introduced. The article was originally published in the Proceedings of the Imperial Academy of Japan in 1926.

This study explored the relationship between fall patterns and fall-related fractures in older adults. A cross-sectional survey was conducted among community-dwelling older adults in Maibara City, Japan, focusing on falls over the past three years. Among the 1,695 reported falls, 176 fractures occurred in 120 individuals. Backward or straight-down and sideways falls were more likely to result in fractures compared to forward falls, with odds ratios (95％ confidence interval) of 3.23 (2.08-5.02) and 3.68 (2.35-5.76), respectively. Falls triggered by slipping or loss of balance had higher fracture rates than those triggered by tripping. Specific fall patterns were associated with particular fractures, such as forearm and patella fractures from forward falls, spine fractures from backward or straight-down falls, and hip fractures from sideways falls. We conclude that the fracture risk varies significantly based on fall patterns, providing insights for enhancing fall prevention strategies.

Iron is an essential element for organisms, but its solubility in soil is often extremely low. Previously, plants were considered to take up iron only after its reduction to ferrous ions. Takagi reported that oat and rice secrete chelating substances that solubilize ferric iron in the rhizosphere for efficient iron uptake. In 1978, Takemoto et al. reported the chemical structure of an iron-chelating compound secreted from barley roots, designated as mugineic acid. Mugineic acid and its derivatives, collectively known as mugineic acid family phytosiderophores (MAs), chelate ferric iron using octahedral hexacoordination. The specific iron uptake system by MAs in graminaceous plants was later classified by Römheld and Marschner as Strategy II, in contrast to Strategy I for reduction-based iron uptake by non-graminaceous plants. Further studies on MAs by Japanese researchers led to the identification of their biosynthetic pathways, corresponding enzymes and encoding genes, their regulation mechanisms, and the production of iron deficiency-tolerant and iron-rich crops.

Cell proliferation is a fundamental characteristic of organisms, driven by the holistic functions of multiple proteins encoded in the genome. However, the individual contributions of thousands of genes and the millions of protein molecules they express to cell proliferation are still not fully understood, even in simple eukaryotes. Here, we present a genome-wide translation map of cells during proliferation in the unicellular alga Cyanidioschyzon merolae, based on the sequencing of ribosome-protected messenger RNA fragments. Ribosome profiling has revealed both qualitative and quantitative changes in protein translation for each gene during cell division, driven by the large-scale reallocation of ribosomes. Comparisons of ribosome footprints from non-dividing and dividing cells allowed the identification of proteins involved in cell proliferation. Given that in vivo experiments on two selected candidate proteins identified a division-phase-specific mitochondrial nucleoid protein and a mitochondrial division protein, further analysis of the candidate proteins may offer key insights into the comprehensive mechanism that facilitate cell and organelle proliferation.

Chloroplasts are photosynthetic organelles that evolved through the endosymbiosis between cyanobacteria-like symbionts and hosts. Many studies have attempted to isolate intact chloroplasts to analyze their morphological characteristics and photosynthetic activity. Although several studies introduced isolated chloroplasts into the cells of different species, their photosynthetic activities have not been confirmed. In this study, we isolated photosynthetically active chloroplasts from the primitive red alga Cyanidioschyzon merolae and incorporated them in cultured mammalian cells via co-cultivation. The incorporated chloroplasts retained their thylakoid structure in intracellular vesicles and were maintained in the cytoplasm, surrounded by the mitochondria near the nucleus. Moreover, the incorporated chloroplasts maintained electron transport activity of photosystem II in cultured mammalian cells for at least 2 days after the incorporation. Our top-down synthetic biology-based approach may serve as a foundation for creating artificially photosynthetic animal cells.