Stereospeific 1H-NMR analysis of trimethylsilyl derivatives of glycerides with a chiral shift reagent

A proton magnetic resonance procedure with tri(3-heptafluorobutyryl-d-camphorato)praseodymium (III) as a chiral shift eagent has been developed to determine the enantimeric purity of monoglycerides 1,2-diglycerides and triglycerides with one mono-unsaturated fatty acid at position $\text{sn-1}$ or $\text{sn-3}$ and two saturated fatty acids at the two other glycerol positions. A model compound, 1-oleoyl-2,3-dipalmitoyl-sn-glycerol, was converted ito the trimethylsilyl either of 2,3-dipalmitoyl-an-glycerol by epoxidation of the double bond, followed by pancreatic hydrolysis and separation and trimethylsilylation of the resulting $\text{sn-1,2}$, and $\text{sn-2,3-}\text{diglycerides}$. This separation becomes feasible by the contribution of the epoxy group to the polarity of the diglyceride. The protons of the trimethysilyl ether group were used for determining the enantiomeric ratio. The addition of a chira shift reagent induces a useful enantiomeric splitting which allows the accurate determination of the ratio of both enantiomers. The trimethylsilyl emers of 1,2-diglycerides are better suited for this purpose than the acetyl compounds. For monoglycetides, the earlier published method with the diaceltates gives a better line separation in ¹H-NMR spectra.     

Evidence that NF-κB and MAPK Signaling Promotes NLRP Inflammasome Activation in Neurons Following Ischemic Stroke

Multi-protein complexes, termed “inflammasomes,” are known to contribute to neuronal cell death and brain injury following ischemic stroke. Ischemic stroke increases the expression and activation of nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) Pyrin domain containing 1 and 3 (NLRP1 and NLRP3) inflammasome proteins and both interleukin (IL)-1β and IL-18 in neurons. In this study, we provide evidence that activation of either the NF-κB and MAPK signaling pathways was partly responsible for inducing the expression and activation of NLRP1 and NLRP3 inflammasome proteins and that these effects can be attenuated using pharmacological inhibitors of these two pathways in neurons and brain tissue under in vitro and in vivo ischemic conditions, respectively. Moreover, these findings provided supporting evidence that treatment with intravenous immunoglobulin (IVIg) preparation can reduce activation of the NF-κB and MAPK signaling pathways resulting in decreased expression and activation of NLRP1 and NLRP3 inflammasomes, as well as increasing expression of anti-apoptotic proteins, Bcl-2 and Bcl-xL, in primary cortical neurons and/or cerebral tissue under in vitro and in vivo ischemic conditions. In summary, these results provide compelling evidence that both the NF-κB and MAPK signaling pathways play a pivotal role in regulating the expression and activation of NLRP1 and NLRP3 inflammasomes in primary cortical neurons and brain tissue under ischemic conditions. In addition, treatment with IVIg preparation decreased the activation of the NF-κB and MAPK signaling pathways, and thus attenuated the expression and activation of NLRP1 and NLRP3 inflammasomes in primary cortical neurons under ischemic conditions. Hence, these findings suggest that therapeutic interventions that target inflammasome activation in neurons may provide new opportunities in the future treatment of ischemic stroke.     

The J-coupling Restrained Molecular Mechanics (JrMM) Protocol - An Efficient Alternative for Deriving DNA Endocyclic Torsion Angle Constraints Part I: Correlation of Endocyclic Torsion Angles and Vicinal Torsion Angle φ1′2′

Abstract

An efficient alternative which makes use of the reliable ³J_1′2′. value to derive the endocyclic torsion angle constraints is proposed in this study. Based on the information embedded in the two plots, (i) the vicinal proton-proton J-couplings, ³J_1′2′., ³J_1′2″., ³J_2′3′., ³J_2”3′ and ³J_3′4′ against the pseudorotation phase angle, and (ii) ³J_1′2″, ³J_2′3′., ³J_2″3′ and ³J_3′4′ against ³J_1′2′; using the calculated J-couplings obtained for a range of sugar geometries of deoxyribose ring in nucleosides and nucleotides encountered along the pseudorotation itinerary [J. van Wijk, B.D. Huckriede, J.H. Ippel and C. Altona, Methods Enzymol. 211, 286–306 (1992)], it is suggested that the vicinal ³J_1′2′ possesses structural information other than the vicinal torsion angle φ_1′2′. This study is divided into two parts. In Part I, a correlation diagram between the endocyclic torsion angles v_i (i=0,1,2,3,4) and the restrained vicinal torsion angle φ_1′2′ is obtained through the use of the J-coupling restrained molecular mechanics (JrMM) protocol. The established φ_1′2′.-v_i correlation shows v_i can be deduced from the reliable ³J_1′2′. value and it forms the basis for developing an alternative protocol to derive endocyclic torsion angle constraints. In Part II of this series, extensive testing demonstrating the validity of the JrMM protocol to derive V_i for defining the sugar geometry of solution DNA molecules is presented.     

Immature and Mature Dengue Serotype 1 Virus Structures Provide Insight into the Maturation Process

Dengue virus is a major human pathogen that has four serotypes (DENV1 to -4). Here we report the cryoelectron microscopy (cryo-EM) structures of immature and mature DENV1 at 6- and 4.5-Å resolution, respectively. The subnanometer-resolution maps allow accurate placement of all of the surface proteins. Although the immature and mature viruses showed vastly different surface protein organizations, the envelope protein transmembrane (E-TM) regions remain in similar positions. The pivotal role of the E-TM regions leads to the identification of the start and end positions of all surface proteins during maturation.     

Structural Changes in Dengue Virus When Exposed to a Temperature of 37°C

Previous binding studies of antibodies that recognized a partially or fully hidden epitope suggest that insect cell-derived dengue virus undergoes structural changes at an elevated temperature. This was confirmed by our cryo-electron microscopy images of dengue virus incubated at 37°C, where viruses change their surface from smooth to rough. Here we present the cryo-electron microscopy structures of dengue virus at 37°C. Image analysis showed four classes of particles. The three-dimensional (3D) map of one of these classes, representing half of the imaged virus population, shows that the E protein shell has expanded and there is a hole at the 3-fold vertices. Fitting E protein structures into the map suggests that all of the interdimeric and some intradimeric E protein interactions are weakened. The accessibility of some previously found cryptic epitopes on this class of particles is discussed.     

Matrix Fixed Charge Density Modulates Exudate Concentration during Cartilage Compression

Electrolyte filtration arises due to the presence of fixed charges in cartilage extracellular matrix glycosaminoglycans (GAGs). Commonly assumed negligible, it can be important for design and interpretation of streaming potential measurements and modeling assumptions. To quantify the scale of this phenomenon, chloride ion concentration in exudate of compressed cartilage was measured by Mohr’s titration and explant GAG content was colorimetrically assayed. Pilot studies indicated that an appropriate strain rate for experiments was 8 × 10⁻³ s⁻¹ to eliminate concerns of exudate evaporation and explant damage (at low and high strain rates, respectively). Exudate chloride concentration of explants equilibrated in 1× PBS was significantly (p < 0.05) lower than the bath chloride concentration at strains of 37.5, 50, and 62.5%, with clear dependence on strain magnitude. Exudate chloride concentration was also significantly lower than that of the bath when 50% strain was applied after equilibration in 0.5, 1, and 2× PBS, with a trend for an increase in this relative difference with decreasing bath concentration (p = 0.065 between 0.5 and 2× PBS). Decreasing exudate chloride concentration correlated negatively with increasing postcompression GAG concentration. No difference between exudate chloride concentration and bath chloride concentration was ever observed for compression of uncharged agarose gel controls. Findings show that exudate from compressed cartilage is dilute relative to the bath due to the presence of matrix fixed charges, and this difference can generate diffusion potentials external to the explant, which may affect streaming potential measurements particularly under conditions of low strain rates and high strains.