Saccharides play critical roles in many forms of cellular activities. Saccharide structures are however complicated and similar, setting a technical hurdle for direct identification. Nanopores, which are emerging single molecule tools sensitive to minor structural differences between analytes, can be engineered to identity saccharides. A hetero‐octameric Mycobacterium smegmatis porin A nanopore containing a phenylboronic acid was prepared, and was able to clearly identify nine monosaccharide types, including D‐fructose, D‐galactose, D‐mannose, D‐glucose, L‐sorbose, D‐ribose, D‐xylose, L‐rhamnose and N‐acetyl‐D‐galactosamine. Minor structural differences between saccharide epimers can also be distinguished. To assist automatic event classification, a machine learning algorithm was developed, with which a general accuracy score of 0.96 was achieved. This sensing strategy is generally suitable for other saccharide types and may bring new insights to nanopore saccharide sequencing.

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ObjectivesCircular RNAs (circRNAs) have emerged as significant biological regulators. Herein, we aimed to elucidate the role of an unidentified circRNA (circPDE4B) that is reportedly downregulated in osteoarthritis (OA) tissues.MethodsThe effects of circPDE4B were explored in human and mouse chondrocytes in vitro. Specifically, RNA pull-down (RPD)-mass spectrometry analysis (MS), immunoprecipitation, glutathione-S-transferase (GST) pull-down, RNA immunoprecipitation and RPD assays were performed to verify the interactions between circPDE4B and the RIC8 guanine nucleotide exchange factor A (RIC8A)/midline 1 (MID1) complex. A mouse model of OA was also employed to confirm the role of circPDE4B in OA pathogenesis in vivo.ResultscircPDE4B regulates chondrocyte cell viability and extracellular matrix metabolism. Mechanistically, FUS RNA binding protein (FUS) was found to promote the splicing of circPDE4B, while downregulation of circPDE4B in OA is partially caused by upstream inhibition of FUS. Moreover, circPDE4B facilitates the association between RIC8A and MID1 by acting as a scaffold to promote RIC8A degradation through proteasomal degradation. Furthermore, ubiquitination of RIC8A at K415 abrogates RIC8A degradation. The circPDE4B–RIC8A axis was observed to play an important role in regulating downstream p38 mitogen-activated protein kinase (MAPK) signalling. Furthermore, delivery of a circPDE4B adeno-associated virus (AAV) abrogates the breakdown of cartilage matrix by medial meniscus destabilisation in mice, whereas a RIC8A AAV induces the opposite effect.ConclusionThis work highlights the function of the circPDE4B–RIC8A axis in OA joints, as well as its regulation of MAPK-p38, suggesting this axis as a potential therapeutic target for OA.

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First-principles calculations were employed to investigate the effect of native defects and a hydrogen-related defect complex on ferromagnetism in an undoped ZnO semiconductor. The results show that the zinc vacancy (V Zn ) could lead to a moment of 1.73 μB in the undoped ZnO supercell, while the oxygen vacancy could not, but the formation energy of the zinc vacancy is much higher than that of the oxygen vacancy. When the hydrogen atom is doped in imperfect ZnO, the formation energy of V Zn +H I sharply decreases, compared with that of V Zn . Meanwhile, the V Zn +H I defect complex can induce a 0.99(0.65) μB moment in the Zn 15 H I O 16 supercell. Furthermore, the total energy of the ZnO supercell with two defect complexes for the ferromagnetic phase is lower than that for the antiferromagnetic phase, and the calculated results show that a strong magnetic coupling exists in the ferromagnetic phase. As an unintentionally doped element, H usually appears in ZnO prepared by many methods. So the ferromagnetism in the ZnO d0 semiconductor most probably arises from the defect complex of the zinc vacancy and H.

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Recent developments concerning large protein nanopores suggest a new approach to structure profiling of native folded proteins. In this work, the large vestibule of Mycobacterium smegmatis porin A (MspA) and calmodulin (CaM), a Ca2+‐binding protein, were used in the direct observation of the protein structure. Three conformers, including the Ca2+‐free, Ca2+‐bound, and target peptide‐bound states of CaM, were unambiguously distinguished. A disease related mutant, CaM D129G was also discriminated by MspA, revealing how a single amino acid replacement can interfere with the Ca2+‐binding capacity of the whole protein. The binding capacity and aggregation effect of CaM induced by different ions (Mg2+/Sr2+/Ba2+/Ca2+/Pb2+/Tb3+) were also investigated and the stability of MspA in extreme conditions was evaluated. This work demonstrates the most systematic single‐molecule investigation of different allosteric conformers of CaM, acknowledging the high sensing resolution offered by the MspA nanopore trap.