In situ proton NMR of glycosidase catalyzed hydrolysis and reverse hydrolysis

Monitoring galactolipid digestion and simultaneous changes in lipid-bile salt micellar organization by real-time NMR spectroscopy

The use of Nuclear Magnetic Resonance spectroscopy for studying lipid digestion in vitro most often consists of quantifying lipolysis products after they have been extracted from the reaction medium using organic solvents. However, the current sensitivity level of NMR spectrometers makes possible to avoid the extraction step and continuously quantify the lipids directly in the reaction medium. We used real-time 1H NMR spectroscopy and guinea pig pancreatic lipase-related protein 2 (GPLRP2) as biocatalyst to monitor in situ the lipolysis of monogalactosyl diacylglycerol (MGDG) in the form of mixed micelles with the bile salt sodium taurodeoxycholate (NaTDC). Residual substrate and lipolysis products (monogalactosyl monoacylglycerol (MGMG); monogalactosylglycerol (MGG) and octanoic acid (OA) were simultaneously quantified throughout the reaction thanks to specific proton resonances. Lipolysis was complete with the release of all MGDG fatty acids. These results were confirmed by thin layer chromatography (TLC) and densitometry after lipid extraction at different reaction times. Using diffusion-ordered NMR spectroscopy (DOSY), we could also estimate the diffusion coefficients of all the reaction compounds and deduce the hydrodynamic radius of the lipid aggregates in which they were present. It was shown that MGDG-NaTDC mixed micelles with an initial hydrodynamic radius rH of 7.3 ± 0.5 nm were changed into smaller micelles of NaTDC-MGDG-MGMG of 2.3 ± 0.5 nm in the course of the lipolysis reaction, and finally into NaTDC-OA mixed micelles (rH of 2.9 ± 0.5 nm) and water soluble MGG. These results provide a better understanding of the digestion of galactolipids by PLRP2, a process that leads to the complete micellar solubilisation of their fatty acids and renders their intestinal absorption possible.

Development of NMR and thermal shift assays for the evaluation of Mycobacterium tuberculosis isocitrate lyase inhibitors

The enzymes isocitrate lyase (ICL) isoforms 1 and 2 are essential for Mycobacterium tuberculosis survival within macrophages during latent tuberculosis (TB). As such, ICLs are attractive therapeutic targets for the treatment of tuberculosis. However, there are few biophysical assays that are available for accurate kinetic and inhibition studies of ICL in vitro. Herein we report the development of a combined NMR spectroscopy and thermal shift assay to study ICL inhibitors for both screening and inhibition constant (IC50) measurement. Operating this new assay in tandem with virtual high-throughput screening has led to the discovery of several new ICL1 inhibitors.

Chemo-enzymatic synthesis of 3-O- (β-d-glycopyranosyl)-sn-glycerols and their evaluation as preservative in cosmetics

d-Glycopyranosyl glycerols are common natural products and exhibit strong biological properties, notably as moisturizing agents in cosmetics. Their chemical synthesis remains tedious thus decreasing their potential industrial and economic development, as well as the study of their structure-function relationships. In this work, the chemo-enzymatic synthesis of three enantiopure 3-O-(β-d-glycopyranosyl)-sn-glycerols was efficiently performed using an original glycosidase from Dictyoglomus thermophilum and their preservatives properties were assessed using a challenge test method. Amongst them, the 3-O-(β-d-glucopyranosyl)-sn-glycerol exhibited a specific anti-fungus activity.

NMR methods for unravelling the spectra of complex mixtures

The main methods for the simplification of the NMR of complex mixtures by selective attenuation/suppression of the signals of certain components are presented. The application of relaxation, diffusion and PSR filters and other techniques to biological samples, pharmaceuticals, foods, living organisms and natural products are illustrated with examples.

Enzymatic synthesis of beta-glucosylglycerol using a continuous-flow microreactor containing thermostable beta-glycoside hydrolase CelB immobilized on coated microchannel walls

beta-Glucosylglycerol (betaGG) has potential applications as a moisturizing agent in cosmetic products. A stereochemically selective method of its synthesis is kinetically controlled enzymatic transglucosylation from a suitable donor substrate to glycerol as acceptor. Here, the thermostable beta-glycosidase CelB from Pyrococcus furiosus was used to develop a microstructured immobilized enzyme reactor for production of betaGG under conditions of continuous flow at 70 degrees C. Using CelB covalently attached onto coated microchannel walls to give an effective enzyme activity of 30 U per total reactor working volume of 25 microL, substrate conversion and formation of transglucosylation product was monitored in dependence of glucosyl donor (2-nitrophenyl-beta-D-glucoside (oNPGlc), 3.0 or 15 mM; cellobiose, 250 mM), the concentration of glycerol (0.25-1.0 M), and the average residence time (0.2-90 s). Glycerol caused a concentration-dependent decrease in the conversion of the glucosyl donor via hydrolysis and strongly suppressed participation of the substrate in the reaction as glucosyl acceptor. The yields of betaGG were > or =80% and approximately 60% based on oNPGlc and cellobiose converted, respectively, and maintained up to near exhaustion of substrate (> or =80%), giving about 120 mM (30 g/L) of betaGG from the reaction of cellobiose and 1 M glycerol. The structure of the transglucosylation products, 1-O-beta-D-glucopyranosyl-rac-glycerol (79%) and 2-O-beta-D-glucopyranosyl-sn-glycerol (21%), was derived from NMR analysis of the product mixture of cellobiose conversion. The microstructured reactor showed conversion characteristics similar to those for a batchwise operated stirred reactor employing soluble CelB. The advantage of miniaturization to the microfluidic format lies in the fast characterization of full reaction time courses for a range of process conditions using only a minimum amount of enzyme.

In situ proton NMR study of acetyl and formyl group migration in mono-O-acyl D-glucose

Acetyl and formyl group migration, mutarotation, and hydrolysis of mono-O-acylated glucose are studied by in situ 1D and 2D (1)H NMR spectroscopy. Alpha-D-glucosyl-1-acetate and alpha-D-glucosyl-1-formate serve as sole starting materials. They are generated in situ by configuration retaining glucosyltransfer from alpha-D-glucosyl-1-phosphate to formate and acetate, which is catalyzed by the Glu-237 --> Gln mutant of Leuconostoc mesenteroides sucrose phosphorylase. Temporary accumulated regio-isomeric mono-O-acyl D-glucoses are identified, characterized, and quantified directly from the reaction mixture. Time courses of the transformations give insight into pH dependence of acyl group migration and mutarotation as well as into the stability of various regioisomers.