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Aquaporins are transmembrane channels that allow for the passive permeation of water and other small molecules across biological membranes. Their channel activities are sensitive to mercury ions. Intriguingly, while most aquaporins are inhibited by mercury ions, several aquaporins are activated by mercury ions. The molecular basis of the opposing aquaporin regulation by mercury remains poorly understood. Herein, we investigated AqpZ inhibition and AQP6 activation upon binding of mercury ions using solid-state NMR (ssNMR) and molecular dynamics (MD) simulations. Based on the structure of the Hg–AqpZ complex constructed by MD simulations and ssNMR, we identified that the pore closure was caused by mercury-induced conformational changes of the key residue R189 in the selectivity filter region, while pore opening was caused by conformational changes of residues H181 and R196 in the selectivity filter region in AQP6. Both conformational changes were caused by the disruption of the H-bond network of R189/R196 by mercury. The molecular details provided a structural basis for mercury-mediated functional changes in aquaporins.

The bacterial mechanosensitive channel of large conductance (MscL) functions as a pressure-relief safety valve to prevent cells from lysing during sudden hypo-osmotic shock. The hydrophobic gate of MscL in the closed state forms a barrier to the permeation of ions and water molecules and can be switched to the open state for releasing solutions and ions. Currently, the gate-constituting residues and the functional role of these residues in the hydrophobic gate of MscL remain elusive and controversial. Here, we employ magic angle spinning solid-state nuclear magnetic resonance (ssNMR) techniques and functional assays to investigate the hydrophobic gate of MscL from Methanosarcina acetivorans(Ma-MscL) in lipid bilayers. We obtain chemical shift assignments of ∼70% residues of Ma-MscL and predict its 3D structure. Based on the structural characterization, we identify that the residues I21–T30 in the transmembrane helix 1 constitute the hydrophobic gate by detecting water distributions in the transmembrane pore using ssNMR H/D exchange and water-edited experiments. By using ssNMR structural characterization and functional assays, we reveal that the packing of aromatic rings of F23 in each subunit of Ma-MscL is critical to the hydrophobic gate, and hydrophilic substitutions of the other functionally important residues A22 and G26 modulate channel gating by attenuating hydrophobicity of constriction of F23.

Nanoparticles with a covalently bound shell of carbohydrate or sulfate groups, respectively, and a polyethylene core were generated by Ni(II)-catalyzed aqueous copolymerization of ethylene with comonomers undec-10-en-1-yl sulfate, undec-10-en-1-yl β-d-glucoside or undec-10-en-1-yl α-d-mannoside, respectively. Via remote substituents of the catalyst, the degree of branching and consequently degree of crystallinity of the polyethylene core of the glyconanoparticles could be controlled. This in turn impacts particle shapes, from spherical to anisotropic platelets, as observed by cryo-transmission electron microscopy. Enzyme-linked lectin assays revealed the mannose-decorated nanocrystals to be efficient multivalent ligands for concavalin A.

•The change of trip volume and social welfare caused by the passenger transfer is analyzed from a theoretical level.•A theoretical model of passenger transfer based on the vertical differentiation model is constructed.•We analyzed the changes of trip volume and social welfare when a ride-hailing platform adopts price subsidies for passengers.•The results of the model are verified by numerical simulation.

MORC3 is linked to inflammatory myopathies and cancer; however, the precise role of MORC3 in normal cell physiology and disease remains poorly understood. Here, we present detailed genetic, biochemical, and structural analyses of MORC3. We demonstrate that MORC3is significantly upregulated in Down syndrome and that genetic abnormalities in MORC3are associated with cancer. The CW domain of MORC3 binds to the methylated histone H3K4 tail, and this interaction is essential for recruitment of MORC3 to chromatin and accumulation in nuclear bodies. We show that MORC3 possesses intrinsic ATPase activity that requires DNA, but it is negatively regulated by the CW domain, which interacts with the ATPase domain. Natively linked CW impedes binding of the ATPase domain to DNA, resulting in a decrease in the DNA-stimulated enzymatic activity. Collectively, our studies provide a molecular framework detailing MORC3 functions and suggest that its modulation may contribute to human disease.

Death Inducer Obliterator 3 (Dido3) is implicated in the maintenance of stem cell genomic stability and tumorigenesis. Here, we show that Dido3 regulates the expression of stemness genes in embryonic stem cells through its plant homeodomain (PHD) finger. Binding of Dido3 PHD to histone H3K4me3 is disrupted by threonine phosphorylation that triggers Dido3 translocation from chromatin to the mitotic spindle. The crystal structure of Dido3 PHD in complex with H3K4me3 reveals an atypical aromatic-cage-like binding site that contains a histidine residue. Biochemical, structural, and mutational analyses of the binding mechanism identified the determinants of specificity and affinity and explained the inability of homologous PHF3 to bind H3K4me3. Together, our findings reveal a link between the transcriptional control in embryonic development and regulation of cell division.

The extended DNA fiber preparation procedure is still imperfect in plants due to the existence of a hard cell wall; thus, high quality of extended DNA fibers for fluorescence in situ hybridization (FISH) analysis is often difficult to be obtained rapidly and efficiently. In this study we have developed a fast and widely effective method to prepare DNA fibers from various plant species and the fibers are suitable for fiber FISH mapping.Fresh young leaves were chopped with a sharp sterile scalpel in a Petri dish that contained ice‐cold nucleus isolation buffer followed by filtration through 33‐μm nylon mesh. Nuclei were obtained by centrifuging the filtrates at high speed (16,000g) for 40 s. Nucleus lysis buffer (0.5% sodium dodecylsulfate, 5 mM ethylenediaminetetraacetic acid, 100 mM Tris, pH7.0) was added to nuclei on slides, and DNA fibers were dragged and extended with a clean coverslip.The key of this method is that liquid nitrogen grinding of leaves is replaced by chopping with a blade in ice‐cold nucleus isolation buffer. With the liquid nitrogen method, over‐ or under‐grinding of leaves occurs more frequently, and DNA fibers with the desired quality are not obtained easily. In contrast, it is easier to release nuclei from cells in nucleus isolation buffer by chopping, which results in fewer nuclei being destroyed. Highly extended, intact, and long DNA fibers can be generated to a great probability with this method. In addition, this method is very simple and rapid, requiring only 20 min for the entire process, and is also safe because poisonous mercaptoethanol is replaced by dithiothreitol. The results of fiber‐FISH with maize genomic DNA and 45S rDNA as probes showed that DNA fiber size as long as 1.96 Mb could be measured. The successful and reliable preparation of maize, wild rice, and barley DNA fibers suitable for FISH mapping proves that this technique is a widely effective approach for obtaining extended DNA fibers in plants.A simple, rapid, safe, and widely effective method for getting extended DNA fibers has been developed in plants. © 2005 Wiley‐Liss, Inc.

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