Application of CP-MAS and liquid-like solid-state NMR experiments for the study of the ripening-associated cell wall changes in tomato

Films composed of white angico gum and chitosan containing chlorhexidine as an antimicrobial agent

Anadenanthera colubrina, popularly known as white angico, is a species extensively cultivated in Brazil, mainly in the cerrado region, including the state of Piauí. This study examines the development of films composed of white angico gum (WAG) and chitosan (CHI) and containing chlorhexidine (CHX), an antimicrobial agent. The solvent casting method was used to prepare films. Different combinations and concentrations of WAG and CHI were used to obtain films with good physicochemical characteristics. Properties such as the in vitro swelling ratio, the disintegration time, folding endurance, and the drug content were determined. The selected formulations were characterised by scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction, and the CHX release time and antimicrobial activity were evaluated. CHX showed a homogenous distribution in all CHI/WAG film formulations. The optimised films showed good physicochemical properties with 80% CHX release over 26 h, which is considered promising for local treatment of severe lesions in the mouth. Cytotoxicity tests of the films did not show toxicity. The antimicrobial and antifungal effects were very effective against the tested microorganisms.

In-cell NMR: Why and how?

NMR spectroscopy has been applied to cells and tissues analysis since its beginnings, as early as 1950. We have attempted to gather here in a didactic fashion the broad diversity of data and ideas that emerged from NMR investigations on living cells. Covering a large proportion of the periodic table, NMR spectroscopy permits scrutiny of a great variety of atomic nuclei in all living organisms non-invasively. It has thus provided quantitative information on cellular atoms and their chemical environment, dynamics, or interactions. We will show that NMR studies have generated valuable knowledge on a vast array of cellular molecules and events, from water, salts, metabolites, cell walls, proteins, nucleic acids, drugs and drug targets, to pH, redox equilibria and chemical reactions. The characterization of such a multitude of objects at the atomic scale has thus shaped our mental representation of cellular life at multiple levels, together with major techniques like mass-spectrometry or microscopies. NMR studies on cells has accompanied the developments of MRI and metabolomics, and various subfields have flourished, coined with appealing names: fluxomics, foodomics, MRI and MRS (i.e. imaging and localized spectroscopy of living tissues, respectively), whole-cell NMR, on-cell ligand-based NMR, systems NMR, cellular structural biology, in-cell NMR… All these have not grown separately, but rather by reinforcing each other like a braided trunk. Hence, we try here to provide an analytical account of a large ensemble of intricately linked approaches, whose integration has been and will be key to their success. We present extensive overviews, firstly on the various types of information provided by NMR in a cellular environment (the "why", oriented towards a broad readership), and secondly on the employed NMR techniques and setups (the "how", where we discuss the past, current and future methods). Each subsection is constructed as a historical anthology, showing how the intrinsic properties of NMR spectroscopy and its developments structured the accessible knowledge on cellular phenomena. Using this systematic approach, we sought i) to make this review accessible to the broadest audience and ii) to highlight some early techniques that may find renewed interest. Finally, we present a brief discussion on what may be potential and desirable developments in the context of integrative studies in biology.

Structural changes in cell wall of Japanese radish accompanied by release of rhamnogalacturonan during pressure cooker heating

Changes in the cell wall of Japanese radish due to heating at 100 °C or 117 °C for 3 h were examined. Signals in ¹³C cross polarization magic angle spinning solid-state NMR (which detects rigid components) showed no differences between heating temperatures. ¹³C pulse saturation transfer magic angle spinning NMR (which detects flexible components) showed clear temperature-dependent changes in the rhamnose side chains of rhamnogalacturonan. Alcohol-insoluble solids isolated from raw samples were heated in water at 100 °C or 117 °C for 3 h. The concentrations of dissolved sugars and metal ions measured after heating in water at 117 °C were greater than in samples heated at 100 °C, indicating that loosening of cell wall structures increased with temperature, likely via degradation and elution of rhamnogalacturonan followed by β-elimination of homogalacturonan, and fewer interactions between cell wall components, including divalent metal ions. Vegetable shape was retained despite fewer interactions.

Assembly of tomato fruit cuticles: a cross-talk between the cutin polyester and cell wall polysaccharides

The cuticle is an essential and ubiquitous biological polymer composite covering aerial plant organs, whose structural component is the cutin polyester entangled with cell wall polysaccharides. The nature of the cutin-embedded polysaccharides (CEPs) and their association with cutin polyester are still unresolved Using tomato fruit as a model, chemical and enzymatic pretreatments combined with biochemical and biophysical methods were developed to compare the fine structure of CEPs with that of the noncutinized polysaccharides (NCPs). In addition, we used tomato fruits from cutin-deficient transgenic lines cus1 (cutin synthase 1) to study the impact of cutin polymerization on the fine structure of CEPs. Cutin-embedded polysaccharides exhibit specific structural features including a high degree of esterification (i.e. methylation and acetylation), a low ramification of rhamnogalacturonan (RGI), and a high crystallinity of cellulose. In addition to decreasing cutin deposition and polymerization, cus1 silencing induced a specific modification of CEPs, especially on pectin content, while NCPs were not affected. This new evidence of the structural specificities of CEPs and of the cross-talk between cutin polymerization and polysaccharides provides new hypotheses concerning the formation of these complex lipopolysaccharide edifices.

Structure and organization within films of arabinoxylans extracted from wheat flour as revealed by various NMR spectroscopic methods

Arabinoxylans (AXs) extracted from wheat flour were characterized by using three different techniques of NMR spectroscopy. Liquid-state (1)H NMR and solid-state (13)C NMR allowed the investigation of the fine structure of the three specific fractions of AXs representative of the structural heterogeneity of AX in wheat tissues. Three pure AX fractions exhibiting an arabinose to xylose ratio of 0.33, 0.53, and 0.73 were compared relative to their substitution feature and also to their assembly into thin films. Measurements of M(2), i.e. the second moment of proton dipolar interactions between the polysaccharide chains, were achieved using time-domain (TD) (1)H NMR at different water contents and temperatures. Transitions of the M(2) values were observed at a certain temperature close to the glass transition temperature T(g) values of AXs in films. Comparison of the different AX films containing various water contents pointed out stronger dipolar interactions for lowly substituted AX. This indicated that, in films, contiguous unsubstituted xylan chains can interact together through hydrogen bonding resulting in a compact structure with small nanopores because of the lower chain motions and the shorter average distances between the lowly substituted AX chains.

Monoclonal antibodies to rhamnogalacturonan I backbone

Monoclonal antibodies were raised against rhamnogalacturonan I backbone, a pectin domain, using Arabidopsis thaliana seed mucilage-derived rhamnogalacturonan I oligosaccharides--BSA conjugates. Two monoclonal antibodies, designated INRA-RU1 and INRA-RU2, selected for further characterization, were specific for the backbone of rhamnogalacturonan I, displaying no binding activity against the other pectin domains i.e. homogalacturonans, galactans or arabinans. A range of oligosaccharides was prepared by enzymatic digestion of rhamnogalacturonan I isolated from Arabidopsis thaliana seed mucilage and from sugar beet pectin, purified by low-pressure chromatography and characterized by high-performance anion-exchange chromatography and mass spectrometry. These rhamnogalacturonan I oligomers were used to characterize the binding site of the two monoclonal antibodies by competitive inhibition. Both INRA-RU1 and INRA-RU2 showed maximal binding to the [-->2)-alpha-L-rhamnosep-(1-->4)-alpha-D-galacturonic acid p-(1-->](7) structural motif but differed in their minimum binding requirement. INRA-RU2 required at least two disaccharide (rhamnose-galacturonic acid) repeats for the antibody to bind, while INRA-RU1 required a minimum of six disaccharide repeats. Furthermore, the binding capacity of INRA-RU1 decreased steeply as the number of disaccharide repeats go beyond seven. Each of these antibodies reacted with hairy regions isolated from sugar beet pectin. Immunofluorescence microscopy indicated that both antibodies can be readily used to detect rhamnogalacturonan I epitopes in various cell wall samples.

Applications of high-resolution solid-state NMR spectroscopy in food science

The principal applications of high-resolution solid-state NMR spectroscopy, in the field of food science, are reviewed, after a short general introduction, mainly focusing on the potential of these investigations, which are, today, routine tools for resolving technological problems. Selected examples of the applications in the field of food science of high-resolution solid-state NMR spectroscopy both in (13)C and in (1)H NMR particularly illustrative of the results obtainable are reported in some detail.

Structural investigation of amylose complexes with small ligands: inter- or intra-helical associations?

Highly crystalline amylose complexes with menthone (1) and linalool (2) were analysed by wide-angle X-ray diffraction and solid-state nuclear magnetic resonance (NMR). The complexes, after partial water desorption in a controlled atmosphere (aw=0.75), displayed a typical V-isopropanol structure, showing the presence of ligand inside or between the helices in the crystalline domains. Sequential washing of the powdered complexes with ethanol before and after desorption permitted probing the intra- and inter-helical inclusions. High resolution magic angle spinning (HRMAS) recordings were used to compare the chemical shifts of free and bound aroma which allowed a proposal that some hydrogen bonding is involved in the amylose complexing. Moreover, it showed that free aroma was completely removed by ethanol washing. Using cross polarization magic angle spinning (CPMAS) and X-ray scattering experiments, it was demonstrated that the V-isopropanol type was retained for linalool whatever the treatment used. On the contrary, the measurement shifts toward the V-6I amylose hydrate (V-h) type for menthone after ethanol washing before the desorption step, reflecting the disappearance of inter-helical associations between menthone and amylose. The stability of the complex prepared with linalool shows that this ligand is more strongly associated to amylose helices. The discrepancies observed in the chemical shifts attributed to carbons C1 and C4 in CPMAS spectra of V-isopropanol and V-h forms could be attributed either to a deformation of the single helix (with possible inclusion of the ligand inside) or to the presence of the ligand between helices (only water molecules are present in the V-h form).

Solid-state 13C NMR spectroscopy studies of xylans in the cell wall of Palmaria palmata (L. Kuntze, Rhodophyta)

The chemical structure and interactions of the cell wall polysaccharides from the red edible seaweed Palmaria palmata were studied by liquid-like magic-angle-spinning (MAS) and cross-polarization MAS (CPMAS) solid-state 13C NMR spectroscopy. The liquid-like MAS and CPMAS 13C NMR spectra of the rehydrated algal powder revealed the presence of beta-(1-->4)/beta-(1-->3)-linked D-xylan with chemical shifts close to those observed in the solution 13C NMR spectrum of the polysaccharide. Observation of mix-linked xylan in the liquid-like MAS 13C NMR spectrum indicated that part of this cell wall polysaccharide is loosely held in the alga. The CPMAS NMR spectrum of the dry algal powder alcohol insoluble residue (AIR) showed broad peaks most of which corresponded to the mix-linked xylan. Hydration of AIR induced a marked increase in the signal resolution also in the CPMAS NMR spectra together with a shift of the C-3 and C-4 signals of the (1-->3)- and (1-->4)-linked xylose, respectively. Such modifications were present in the spectrum of hydrated (1-->3)-linked xylan from the green seaweed Caulerpa taxifolia and absent in that of (1-->4)-linked xylan from P. palmata. This result emphasizes the important role of (1-->3) linkages on the mix-linked xylan hydration-induced conformational rearrangement. The mix-linked xylan signals were observed in the CPMAS NMR spectrum of hydrated residues obtained after extensive extractions by NaOH or strong chaotropic solutions indicating strong hydrogen bonds or covalent linkages. T(1 rho) relaxations were measured close or above 10 ms for the mix-linked xylan in the dry and hydrated state in AIR and indicated that the overall xylan chains likely remain rigid. Rehydration of the mix-linked xylan lead to a decrease in the motion of protons bounded to the C-1 and C-4 carbons of the (1-->4)-linked xylose supporting the re-organization of the xylan chains under hydration involving junction-zones held by hydrogen bonds between adjacent (1-->4)-linked xylose blocks. The CPMAS NMR spectrum of both dry and rehydrated residues obtained after NaOH and HCl extractions demonstrated the presence of cellulose and (1-->4)-linked xylans. The structures of the different polysaccharides are discussed in relation to their interactions and putative functions on the cell wall mechanical properties in P. palmata.