Participation of lipopolysaccharide in hyperplasic adipose expansion: Involvement of NADPH oxidase/ROS/p42/p44 MAPK‐dependent Cyclooxygenase‐2

Obesity is a world‐wide problem, especially the child obesity, with the complication of various metabolic diseases. Child obesity can be developed as early as the age between 2 and 6. The expansion of fat mass in child age includes both hyperplasia and hypertrophy of adipose tissue, suggesting the importance of proliferation and adipogenesis of preadipocytes. The changed composition of gut microbiota is associated with obesity, revealing the roles of lipopolysaccharide (LPS) on manipulating adipose tissue development. Studies suggest that LPS enters the circulation and acts as a pro‐inflammatory regulator to facilitate pathologies. Nevertheless, the underlying mechanisms behind LPS‐modulated obesity are yet clearly elucidated. This study showed that LPS enhanced the expression of cyclooxygenase‐2 (COX‐2), an inflammatory regulator of obesity, in preadipocytes. Pretreating preadipocytes with the scavenger of reactive oxygen species (ROS) or the inhibitors of NADPH oxidase or p42/p44 MAPK markedly decreased LPS‐stimulated gene expression of COX‐2 together with the phosphorylation of p47^phox and p42/p44 MAPK, separately. LPS activated p42/p44 MAPK via NADPH oxidase‐dependent ROS accumulation in preadipocytes. Reduction of intracellular ROS or attenuation of p42/p44 MAPK activation both reduced LPS‐mediated COX‐2 expression and preadipocyte proliferation. Moreover, LPS‐induced preadipocyte proliferation and adipogenesis were abolished by the inhibition of COX‐2 or PEG₂ receptors. Taken together, our results suggested that LPS enhanced the proliferation and adipogenesis of preadipocytes via NADPH oxidase/ROS/p42/p44 MAPK‐dependent COX‐2 expression.     

生物土壤结皮的分布影响因子及其监测

生物土壤结皮在荒漠化地区广泛分布。本文详细论述了生物土壤结皮的分布规律及其影响因素,如海拔高度、土壤、维管植物群落水分条件和干扰,以及生物土壤结皮在生态系统和景观变化监测和评价中的作用等。同时对中国西北地区生物土壤结皮的生态学研究和开发应用提供了研究的重点和方向。     

Functional roles of ATP-binding residues in the catalytic site of human mitochondrial NAD(P)+-dependent malic enzyme

Human mitochondrial NAD(P)+-dependent malic enzyme is inhibited by ATP. The X-ray crystal structures have revealed that two ATP molecules occupy both the active and exo site of the enzyme, suggesting that ATP might act as an allosteric inhibitor of the enzyme. However, mutagenesis studies and kinetic evidences indicated that the catalytic activity of the enzyme is inhibited by ATP through a competitive inhibition mechanism in the active site and not in the exo site. Three amino acid residues, Arg165, Asn259, and Glu314, which are hydrogen-bonded with NAD+ or ATP, are chosen to characterize their possible roles on the inhibitory effect of ATP for the enzyme. Our kinetic data clearly demonstrate that Arg165 is essential for catalysis. The R165A enzyme had very low enzyme activity, and it was only slightly inhibited by ATP and not activated by fumarate. The values of K(m,NAD) and K(i,ATP) to both NAD+ and malate were elevated. Elimination of the guanidino side chain of R165 made the enzyme defective on the binding of NAD+ and ATP, and it caused the charge imbalance in the active site. These effects possibly caused the enzyme to malfunction on its catalytic power. The N259A enzyme was less inhibited by ATP but could be fully activated by fumarate at a similar extent compared with the wild-type enzyme. For the N259A enzyme, the value of K(i,ATP) to NAD+ but not to malate was elevated, indicating that the hydrogen bonding between ATP and the amide side chain of this residue is important for the binding stability of ATP. Removal of this side chain did not cause any harmful effect on the fumarate-induced activation of the enzyme. The E314A enzyme, however, was severely inhibited by ATP and only slightly activated by fumarate. The values of K(m,malate), K(m,NAD), and K(i,ATP) to both NAD+ and malate for E314A were reduced to about 2-7-folds compared with those of the wild-type enzyme. It can be concluded that mutation of Glu314 to Ala eliminated the repulsive effects between Glu314 and malate, NAD+, or ATP, and thus the binding affinities of malate, NAD+, and ATP in the active site of the enzyme were enhanced.     

Compositional changes in cell wall polysaccharides from chilled and non-chilled cucumber fruit

Cell wall carbohydrate composition and 1-aminocyclopropane-1-carboxylic acid (ACC) content have been determined in chilled (2.5°) and non-chilled (12.5°) cucumber fruit. The major compositional change that accompanied the increased capability for ACC synthesis during chilling was a diminished loss of galactose residues, relative to the loss which occurred at 12.5°. However, the loss of galactose residues increased markedly when fruit were transferred from 2.5° to 20°, and wall galactose levels eventually declined to similar levels in both chilled and non-chilled fruit. Rhamnose, arabinose, xylose, mannose and cellulose content of walls was similar in chilled and non-chilled fruit and did not change substantially upon transfer of fruit to 20°. Upon transfer of chilled fruit from 2.5° to 20°, an increase in the relative amount of galacturonic acid in cell walls occurred; this change did not occur in non-chilled fruit. Thus, chilling stress results in a rapid change in the neutral sugar and galacturonic acid composition of cell wall pectic polysaccharides upon warming.     

NMR assignments of the C-terminal domain of human galectin-8

Galectins recognize β-galectosides to promote a variety of cellular functions. Despite their sequence variations, all galectins share the same carbohydrate recognition domains (CRD) and their modes of ligand recognition at a structural level are essentially identical. Human galectin 8 plays an important role in numerous cancer and immune responses. It consists of two CRDs that are connected via a flexible linker. The substrate affinities and specificities of the N- and C-terminal domains are quite different. In order to investigate the structural basis of their substrate specificities, we complete the NMR ¹H, ¹³C, and ¹⁵N chemical shift assignments of C-terminal domain of human galectin-8 (hG8C).     

Li–Ti Cation Mixing Enhanced Structural and Performance Stability of Li‐Rich Layered Oxide

Li‐rich layered metal oxides are one type of the most promising cathode materials in lithium‐ion batteries but suffer from severe voltage decay during cycling because of the continuous transition metal (TM) migration into the Li layers. A Li‐rich layered metal oxide Li_1.2Ti_0.26Ni_0.18Co_0.18Mn_0.18O₂ (LTR) is hereby designed, in which some of the Ti⁴⁺ cations are intrinsically present in the Li layers. The native Li–Ti cation mixing structure enhances the tolerance for structural distortion and inhibits the migration of the TM ions in the TMO₂ slabs during (de)lithiation. Consequently, LTR exhibits a remarkable cycling stability of 97% capacity retention after 182 cycles, and the average discharge potential drops only 90 mV in 100 cycles. In‐depth studies by electron energy loss spectroscopy and aberration‐corrected scanning transmission electron microscopy demonstrate the Li–Ti mixing structure. The charge compensation mechanism is uncovered with X‐ray absorption spectroscopy and explained with the density function theory calculations. These results show the superiority of introducing transition metal ions into the Li layers in reinforcing the structural stability of the Li‐rich layered metal oxides. These findings shed light on a possible path to the development of Li‐rich materials with better potential retention and a longer lifespan.     

Protection of cullin-RING E3 ligases by CSN-UBP12

Neddylation, a process that conjugates the ubiquitin-like polypeptide NEDD8 to cullin proteins, activates cullin-RING ubiquitin ligases (CRLs). Deneddylation, in which the COP9 signalosome (CSN) removes NEDD8 from cullins, inactivates CRLs. However, genetic studies of CSN function conclude that deneddylation also promotes CRL activity. It has been proposed that a cyclic transition through neddylation and deneddylation is required for the regulation of CRL activity in vivo. Recent discoveries suggest that an additional level of complexity exists, whereby CRL components are targets for degradation, mediated either by autocatalytic ubiquitination or by unknown mechanisms. Deneddylation by CSN and deubiquitylation by CSN-associated ubiquitin-specific protease 12 protect CRL components from cellular depletion, thus maintaining the physiological CRL activities.