Isomadecassoside, a New Ursane-Type Triterpene Glycoside from Centella asiatica Leaves, Reduces Nitrite Levels in LPS-Stimulated Macrophages

A madecassoside-rich fraction obtained from the industrial purification of Centella asiatica leaves afforded a new triterpene glycoside, named isomadecassoside (4), characterized by an ursane-type skeleton and migration of the double bond at Δ20(21) in ring E. The structure of isomadecassoside was established by means of HR-ESIMS and detailed analysis of 1D and 2D NMR spectra, which allowed a complete NMR assignment. Studies on isolated J774A.1 macrophages stimulated by LPS revealed that isomadecassoside (4) inhibited nitrite production at non-cytotoxic concentrations, thus indicating an anti-inflammatory effect similar to that of madecassoside.

Structural basis of the dynamic human CEACAM1 monomer-dimer equilibrium

Human (h) carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) function depends upon IgV-mediated homodimerization or heterodimerization with host ligands, including hCEACAM5, hTIM-3, PD-1, and a variety of microbial pathogens. However, there is little structural information available on how hCEACAM1 transitions between monomeric and dimeric states which in the latter case is critical for initiating hCEACAM1 activities. We therefore mutated residues within the hCEACAM1 IgV GFCC′ face including V39, I91, N97, and E99 and examined hCEACAM1 IgV monomer-homodimer exchange using differential scanning fluorimetry, multi-angle light scattering, X-ray crystallography and/or nuclear magnetic resonance. From these studies, we describe hCEACAM1 homodimeric, monomeric and transition states at atomic resolution and its conformational behavior in solution through NMR assignment of the wildtype (WT) hCEACAM1 IgV dimer and N97A mutant monomer. These studies reveal the flexibility of the GFCC’ face and its important role in governing the formation of hCEACAM1 dimers and selective heterodimers.

Insights into alginate degradation through the characterization of a thermophilic exolytic alginate lyase

Enzymatic depolymerization of seaweed polysaccharides is gaining interest for the production of functional oligosaccharides and fermentable sugars. Herein, we describe a thermostable alginate lyase that belongs to Polysaccharide Lyase family 17 (PL17) and was derived from an Arctic Mid-Ocean Ridge (AMOR) metagenomics dataset. This enzyme, AMOR_PL17A, is a thermostable exolytic oligoalginate lyase (EC 4.2.2.26), which can degrade alginate, poly β-d-mannuronate and poly α-l-guluronate within a broad range of pH, temperature and salinity conditions. Site-directed mutagenesis showed that tyrosine Y251, previously suggested to act as catalytic acid, indeed is essential for catalysis; whereas mutation of tyrosine Y446, previously proposed to act as catalytic base, did not affect enzyme activity. The observed reaction products are protonated and deprotonated forms of the 4,5-unsaturated uronic acid monomer, Δ, two hydrates of DEH (4-deoxy-l-erythro-5-hexulosuronate), which are formed after ring opening and, finally, two epimers of a 5-membered hemiketal called 4-deoxy-d-manno-hexulofuranosidonate (DHF) formed through intramolecular cyclisation of hydrated DEH. The detection and NMR assignment of these hemiketals refine our current understanding of alginate degradation. Importance The potential markets for seaweed-derived products and seaweed processing technologies are growing, yet commercial enzyme-cocktails for complete conversion of seaweed to fermentable sugars are not available. Such an enzyme-cocktail would require the catalytic properties of a variety of different enzymes, where fucoidanases, laminarinases and cellulases together with endo- and exo-acting alginate lyases would be the key enzymes. Here we present an exo-acting alginate lyase that efficiently produces monomeric sugars from alginate. Since it is only the second characterized exo-acting alginate lyase capable of degrading alginate at industrially relevant higher temperatures of 60 °C, this enzyme may be of great biotechnological and industrial interest. In addition, in-depth NMR-based structural elucidation reveal previously undescribed rearrangement products of the unsaturated monomeric sugars generated from exo-acting lyases. The insight provided by the NMR assignment of these products facilitates future assessment of product formation by alginate lyases.

Paramagnetic solid-state NMR assignment and novel chemical conversion of the aldehyde group to dihydrogen ortho ester and hemiacetal moieties in copper(ii)- and cobalt(ii)-pyridinecarboxaldehyde complexes

The complex chemical functionalization of the aldehyde group was elucidated in copper and cobalt complexes for 4- and 3-pyridinecarboxaldehyde ligands.

A combined theoretical/experimental study highlighting the formation of carbides on Ru nanoparticles during CO hydrogenation

According to advanced 13C MAS NMR experiments and DFT investigations of multi-step pathways as well as DFT-based NMR assignment of experimental spectra, it is shown that carbide formation can occur on ruthenium NPs during CO bond cleavage.

Complete NMR assignment and analysis of molecular structural changes of β–O–4 lignin oligomer model compounds in organic media with different water content

The conformation of lignin in solvents is major key factors governing the physicochemical properties of aromatic polymers. However, the conformational changes of lignin in good and poor solvents is not clearly understood at the molecular level. In this study, short- (DP 2.77) and long-chain (DP 4.49) lignin oligomer model compounds composed solely of interunit β–O–4 bonds with a narrow polydispersity were synthesized, and their NMR spectra were recorded to evaluate the molecular structural changes induced by addition of water to an organic solvent. The spectral signals were completely assigned in DMSO-d6 and D2O by applying 2D 1H–13C HSQC, HMBC, and long-range heteronuclear single quantum multiple bond correlation (LR-HSQMBC). The conformation of the long- and short-chain lignin models were analyzed by 2D 1H–1H ROESY. In all the solvent systems, consisting of DMSO-d6 and containing 0–90% volume of acetic acid-d4 buffer in D2O (pD 5.0), the lignin models were found to have folded conformations, but more compact structures were observed in D2O compared with DMSO-d6.