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Many organisms reductively assimilate selenite to synthesize selenoprotein. Although the thioredoxin system, consisting of thioredoxin 1 (TrxA) and thioredoxin reductase with NADPH, can reduce selenite and is considered to facilitate selenite assimilation, the detailed mechanism remains obscure. Here, we show that selenite was reduced by the thioredoxin system from Pseudomonas stutzeri only in the presence of the TrxA (PsTrxA), and this system was specific to selenite among the oxyanions examined. Mutational analysis revealed that Cys33 and Cys36 residues in PsTrxA are important for selenite reduction. Free thiol-labeling assays suggested that Cys33 is more reactive than Cys36. Mass spectrometry analysis suggested that PsTrxA reduces selenite via PsTrxA-SeO intermediate formation. Furthermore, an in vivo formate dehydrogenase activity assay in Escherichia coli with a gene disruption suggested that TrxA is important for selenoprotein biosynthesis. The introduction of PsTrxA complemented the effects of TrxA disruption in E. coli cells, only when PsTrxA contained Cys33 and Cys36. Based on these results, we proposed the early steps of the link between selenite and selenoprotein biosynthesis via the formation of TrxA–selenium complexes.

Lysophosphatidic acid acyltransferase (LPAAT) introduces fatty acyl groups into the sn-2 position of membrane phospholipids (PLs). Various bacteria produce multiple LPAATs, whereas it is believed that Escherichia coli produces only one essential LPAAT homolog, PlsC—the deletion of which is lethal. However, we found that E. coli possesses another LPAAT homolog named YihG. Here, we show that overexpression of YihG in E. coli carrying a temperature-sensitive mutation in plsC allowed its growth at non-permissive temperatures. Analysis of the fatty acyl composition of PLs from the yihG-deletion mutant (∆yihG) revealed that endogenous YihG introduces the cis-vaccenoyl group into the sn-2 position of PLs. Loss of YihG did not affect cell growth or morphology, but ∆yihG cells swam well in liquid medium in contrast to wild-type cells. Immunoblot analysis showed that FliC was highly expressed in ∆yihG cells, and this phenotype was suppressed by expression of recombinant YihG in ∆yihG cells. Transmission electron microscopy confirmed that the flagellar structure was observed only in ∆yihG cells. These results suggest that YihG has specific functions related to flagellar formation through modulation of the fatty acyl composition of membrane PLs.

Biodegradable nanocarriers based on polysaccharide-derived amphiphilic copolymers are promising candidates to enhance drug solubility and stability. This study aimed to design a novel amphiphilic carrier based on enzymatic polymerization-derived exopolysaccharides, α-1,3-glucan. Glycosyltransferase I from Streptococcus mutans was used to synthesize α-1,3-glucan, and the amphiphilic α-1,3-glucan-graft-poly(ε-caprolactone) (Glucan-g-PCL) copolymer was synthesized via a homogeneous ring-opening polymerization (ROP) in ionic liquid, 1-butyl-3-methylimidazolium chloride. The chemical structures and physical properties of Glucan-g-PCL copolymer were characterized by FT-IR, 1H NMR, XRD, and TGA. The self-assembly behavior of the amphiphilic α-1,3-glucan derivative was investigated by fluorescence probe. The results showed that Glucan-g-PCL exhibited a low critical aggregation concentration (CAC) and formed core-shell structured nanostructure via self-assembly. Quercetin (Qu), a hydrophobic active component, was successfully encapsulated within the Glucan-g-PCL micelle-like nanostructure, showing efficient encapsulation and dispersion in water. Qu/Glucan-g-PCL micelle-like nanostructure (Qu/M) was characterized by DLS, TEM, FT-IR, and XRD. FT-IR and XRD analyses showed that Qu was present in an amorphous state in the formulation and without any chemical reactions during the sample preparation procedures. In addition, the antioxidant properties of the Qu/M were investigated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method, and significantly improved antioxidant activity was observed for Qu/M compared to Qu/water. The utilization of Glucan-g-PCL nanostructure encapsulation opens up new possibilities for enhancing and expanding the practical applications of quercetin and α-1,3-glucan.Graphic Abstract

Polysaccharide-based amphiphilic copolymers self-assemble in water to form micelle-like structures. They are expected to be used as nanocarriers in the biomedical field owing to their biocompatibility, biodegradability, and low toxicity. α-1,3-Glucan is a water-insoluble glucose homopolymer that can be generated through environmentally friendly enzymatic polymerization and easily purified without using organic solvents. Thus, it has attracted attention as a new bio-based material. In this study, we developed new nanomicelles based on α-1,3-glucan. Glycosyltransferase I from Streptococcus mutans was used to synthesize α-1,3-glucan, and a series of amphiphilic α-1,3-glucan-based graft copolymers (α-1,3-glucan-g-PLA) were synthesized with different L-Lactide supply ratios in the ionic liquid BmimCl. The results of FT-IR, 1H NMR, 13C NMR, XRD, and TGA verified that the reaction proceeded successfully. These amphiphilic α-1,3-glucan derivatives with low critical micelle concentrations can self-assemble to form core–shell structural micelles of various sizes (approximately 57–125 nm) in water. Furthermore, the self-assembled micelles were investigated as drug carriers using prednisone acetate (PA) as a model drug, and their sustained drug release behavior for 9 days was confirmed. These results revealed that the synthesized self-assembled micelles have promising potential as new carriers for the efficient delivery of hydrophobic drugs.