Structural, Thermodynamic, and Kinetic Analyses of Tetrahydrooxazine-derived Inhibitors Bound to β-Glucosidases

Structural and mutational analysis of glycoside hydrolase family 1 Br2 β-glucosidase derived from bovine rumen metagenome

Ruminant animals rely on the activities of β-glucosidases from residential microbes to convert feed fibers into glucose for further metabolic uses. In this report, we determined the structures of Br2, which is a glycoside hydrolase family 1 β-glucosidase from the bovine rumen metagenome. Br2 folds into a classical (β/α)8-TIM barrel domain but displays unique structural features at loop β5→α5 and α-helix 5, resulting in different positive subsites from those of other GH1 enzymes. Br2 exhibited the highest specificity toward laminaritriose, suggesting its involvement in β-glucan hydrolysis in digested feed. We then substituted the residues at subsites +1 and + 2 of Br2 with those of Halothermothrix orenii β-glucosidase. The C170E and C221T mutations provided favorable interactions with glucooligosaccharide substrates at subsite +2, while the A219N mutation probably improved the substrate preference for cellobiose and gentiobiose relative to laminaribiose at subsite +1. The N407Y mutation increased the affinity toward cellooligosaccharides. These results give further insights into the molecular determinants responsible for substrate specificity in GH1 β-glucosidases and may provide a basis for future enzyme engineering applications.

Cloning, biochemical characterization and molecular docking of novel thermostable β-glucosidase BglA9 from Anoxybacillus ayderensis A9 and its application in de-glycosylation of Polydatin

This study reports a novel BglA9 gene of 1345 bp encoding β-glucosidase from Anoxybacillus ayderensis A9, which was amplified and expressed in E. coli BL21 (DE3): pLysS cells, purified with Ni-NTA column having molecular weight of 52.6 kDa and was used in the bioconversion of polydatin to resveratrol. The kinetic parameters values using pNPG as substrate were K_m (0.28 mM), V_max (43.8 μmol/min/mg), k_cat (38.43 s^-1) and k_cat/K_m (135.5 s^-1 mM^-1). The BglA9 was active in a broad pH range and had an activity half-life around 24 h at 50 °C. The de-glycosylation efficiency of BglA9 for polydatin was determined by estimating the amount of glucose released after enzymatic reaction by a dinitrosalicylic acid (DNS) assay. The kinetic parameters of BglA9 for polydatin were 5.5 mM, 20.84 μmol/min/mg, 18.28 s^-1and 3.27 s^-1 mM^-1 for K_m, V_max, k_cat, and k_cat/K_m values, respectively. The K_i value for glucose was determined to be 1.7 M. The residues Gln19, His120, Glu355, Glu409, Glu178, Asn222 may play a crucial role in the deglycosylation as revealed by the 3D structure of enzyme docked with polydatin.

The Functionally Characterization of Putative Genes Involved in the Formation of Mannose in the Aplanospore Cell Wall of Haematococcus pluvialis (Volvocales, Chlorophyta)

Unicellular volvocalean green algal Haematococcus pluvialis, known as astaxanthin rich microalgae, transforms into aplanospore stage from the flagellate stage when exposed to the stress environments. However, the mechanism of the formation of aplanospore cell wall, which hinders the extraction of astaxanthin and the genetic manipulation is still unclear. In this study, the cell wall components under salicylic acid and high light stresses were explored, and cellulose was considered the main component in the flagellates, which changed gradually into mannose in the aplanospore stages. During the period, the genes related to the cellulose and mannose metabolisms were identified based on the RNA-seq data, which presented a similar expression pattern. The positive correlations were observed among these studied genes by Pearson Correlation (PC) analysis, indicating the coordination between pathways of cellulose and mannose metabolism. The study firstly explored the formation mechanism of aplanospore cell wall, which might be of scientific significance in the study of H. pluvialis.

Thermodynamic profiling for fragment-based lead discovery and optimization

Introduction: The enthalpic and entropic components of the ligand-protein binding free energy reflect the type and quality of the interactions and relate to the physicochemical properties of the ligands. These findings have significance in medicinal chemistry optimizations since they suggest that the thermodynamic profiling of the binding may help monitor and control the unfavorable size and hydrophobicity increase typically accompanying affinity improvements and leading to suboptimal pharmacokinetic properties.Areas covered: This review describes the ligand-protein binding event in terms of elementary steps, their associated interactions, and their enthalpic and entropic consequences. The relationships among the breaking and forming interactions, the binding thermodynamic profile, and the physicochemical properties of the ligands are also discussed.Expert opinion: Analysis of the size dependence of available affinity and favorable enthalpy highlights the limitation of the simultaneous optimization of these quantities. Indeed, moderate, rather than very high affinities can be conciliated with favorable physicochemical and pharmacokinetic profiles as it is supported by the affinity range of historical oral drugs. Although thermodynamic quantities are not suitable endpoints for medicinal chemistry optimizations owing to the complexity of the binding thermodynamics, thermodynamic profiling together with structural studies can be advantageously used to understand the details of the binding process and to optimize it.

Efficient Hydrolytic Breakage of β-1,4-Glycosidic Bond Catalyzed by a Difunctional Magnetic Nanocatalyst

A novel difunctional magnetic nanocatalyst (DMNC) was prepared and used to catalyse the hydrolytic breakage of β-1,4-glycosidic bonds. The functional nanoparticle displayed excellent catalytic activity for hydrolysis of cellobiose to glucose under moderate conditions. The conversion of cellobiose and yield of glucose could reach 95.3 and 91.1 %, respectively, for a reaction time of 6 h at pH 4.0 and 130°C. DMNC was also an efficient catalyst for the hydrolysis of cellulose: 53.9 % microcrystalline cellulose was hydrolyzed, and 45.7 % reducing sugar was obtained at pH 4.0 and 130°C after 10 h. The magnetic catalyst could be recycled and reused five times without significant loss of catalytic activity.

Motif-guided identification of a glycoside hydrolase family 1 α-L-arabinofuranosidase in Bifidobacterium adolescentis

Members of glycoside hydrolase family 1 (GH1) cleave glycosidic linkages with a variety of physiological roles. Here we report a unique GH1 member encoded in the genome of Bifidobacterium adolescentis ATCC 15703. This enzyme, BAD0156, was identified from over 2,000 GH1 sequences accumulated in a database by a genome mining approach based on a motif sequence. A recombinant BAD0156 protein was characterized to confirm that this enzyme alone specifically hydrolyzes p-nitrophenyl-α-L-arabinofuranoside among the 24 p-nitrophenyl-glycosides examined. Among natural glycosides, α-1,5-linked arabino-oligosaccharides served as substrates, but arabinan, debranched arabinan, arabinoxylan, and arabinogalactan did not. A time course analysis of arabino-oligosaccharide hydrolysis indicated that BAD0156 is an exo-acting enzyme. These results suggest that BAD0156 is an α-L-arabinofuranosidase. This is the first report of a GH1 enzyme that acts specifically on arabinosides, providing information on GH1 substrate specificity.

Development of inhibitors as research tools for carbohydrate-processing enzymes

Carbohydrates, which are present in all domains of life, play important roles in a host of cellular processes. These ubiquitous biomolecules form highly diverse and often complex glycan structures without the aid of a template. The carbohydrate structures are regulated solely by the location and specificity of the enzymes responsible for their synthesis and degradation. These enzymes, glycosyltransferases and glycoside hydrolases, need to be functionally well characterized in order to investigate the structure and function of glycans. The use of enzyme inhibitors, which target a particular enzyme, can significantly aid this understanding, and may also provide insights into therapeutic applications. The present article describes some of the approaches used to design and develop enzyme inhibitors as tools for investigating carbohydrate-processing enzymes.

The crystallization and structural analysis of cellulases (and other glycoside hydrolases): strategies and tactics

The three-dimensional (3-D) structures of cellulases, and other glycoside hydrolases, are a central feature of research in carbohydrate chemistry and biochemistry. 3-D structure is used to inform protein engineering campaigns, both academic and industrial, which are typically used to improve the stability or activity of an enzyme. Examples of classical protein engineering goals include higher thermal stability, reduced metal-ion dependency, detergent and protease resistance, decreased product inhibition, and altered specificity. 3-D structure may also be used to interpret the behavior of enzyme variants that are derived from screening or random mutagenesis approaches, with a view to establishing an iterative design process. In other areas, 3-D structure is used as one of the many tools to probe enzymatic catalysis, typically dovetailing with physical organic chemistry approaches to provide complete reaction mechanisms for enzymes by visualizing catalytic site interactions at different stages of the reaction. Such mechanistic insight is not only fundamentally important, impacting on inhibitor and drug design approaches with ramifications way beyond cellulose hydrolysis, but also provides the framework for the design of enzyme variants to use as biocatalysts for the synthesis of bespoke oligosaccharides. Here we review some of the strategies and tactics that may be applied to the X-ray structure solution of cellulases (and other carbohydrate-active enzymes). The general approach is first to decide why you are doing the work, then to establish correct domain boundaries for truncated constructs (typically the catalytic domain only), and finally to pursue crystallization of pure, homogeneous, and monodisperse protein with appropriate ligand and additive combinations. Cellulase-specific strategies are important for the delineation of domain boundaries, while glycoside hydrolases generally also present challenges and opportunities for the selection and optimization of ligands to both aid crystallization, and also provide structural and mechanistic insight. As the many roles for plant cell wall degrading enzymes increase, so does the need for rapid high-quality structure determination to provide a sound structural foundation for understanding mechanism and specificity, and for future protein engineering strategies.

Aglycone specificity of Thermotoga neapolitana β-glucosidase 1A modified by mutagenesis, leading to increased catalytic efficiency in quercetin-3-glucoside hydrolysis

BACKGROUND

The thermostable β-glucosidase (TnBgl1A) from Thermotoga neapolitana is a promising biocatalyst for hydrolysis of glucosylated flavonoids and can be coupled to extraction methods using pressurized hot water. Hydrolysis has however been shown to be dependent on the position of the glucosylation on the flavonoid, and e.g. quercetin-3-glucoside (Q3) was hydrolysed slowly. A set of mutants of TnBgl1A were thus created to analyse the influence on the kinetic parameters using the model substrate para-nitrophenyl-β-D-glucopyranoside (pNPGlc), and screened for hydrolysis of Q3.

RESULTS

Structural analysis pinpointed an area in the active site pocket with non-conserved residues between specificity groups in glycoside hydrolase family 1 (GH1). Three residues in this area located on β-strand 5 (F219, N221, and G222) close to sugar binding sub-site +2 were selected for mutagenesis and amplified in a protocol that introduced a few spontaneous mutations. Eight mutants (four triple: F219L/P165L/M278I, N221S/P165L/M278I, G222Q/P165L/M278I, G222Q/V203M/K214R, two double: F219L/K214R, N221S/P342L and two single: G222M and N221S) were produced in E. coli, and purified to apparent homogeneity. Thermostability, measured as Tm by differential scanning calorimetry (101.9°C for wt), was kept in the mutated variants and significant decrease (ΔT of 5-10°C) was only observed for the triple mutants. The exchanged residue(s) in the respective mutant resulted in variations in KM and turnover. The KM-value was only changed in variants mutated at position 221 (N221S) and was in all cases monitored as a 2-3 × increase for pNPGlc, while the KM decreased a corresponding extent for Q3.Turnover was only significantly changed using pNPGlc, and was decreased 2-3 × in variants mutated at position 222, while the single, double and triple mutated variants carrying a mutation at position 221 (N221S) increased turnover up to 3.5 × compared to the wild type. Modelling showed that the mutation at position 221, may alter the position of N291 resulting in increased hydrogen bonding of Q3 (at a position corresponding to the +1 subsite) which may explain the decrease in KM for this substrate.

CONCLUSION

These results show that residues at the +2 subsite are interesting targets for mutagenesis and mutations at these positions can directly or indirectly affect both KM and turnover. An affinity change, leading to a decreased KM, can be explained by an altered position of N291, while the changes in turnover are more difficult to explain and may be the result of smaller conformational changes in the active site.

Imino sugars and glycosyl hydrolases: historical context, current aspects, emerging trends

Forty years of discoveries and research on imino sugars, which are carbohydrate analogues having a basic nitrogen atom instead of oxygen in the sugar ring and, acting as potent glycosidase inhibitors, have made considerable impact on our contemporary understanding of glycosidases. Imino sugars have helped to elucidate the catalytic machinery of glycosidases and have refined our methods and concepts of utilizing them. A number of new aspects have emerged for employing imino sugars as pharmaceutical compounds, based on their profound effects on metabolic activities in which glycosidases are involved. From the digestion of starch to the fight against viral infections, from research into malignant diseases to potential improvements in hereditary storage disorders, glycosidase action and inhibition are essential issues. This account aims at combining general developments with a focus on some niches where imino sugars have become useful tools for glycochemistry and glycobiology.

β-Glucosidases

β-Glucosidases (3.2.1.21) are found in all domains of living organisms, where they play essential roles in the removal of nonreducing terminal glucosyl residues from saccharides and glycosides. β-Glucosidases function in glycolipid and exogenous glycoside metabolism in animals, defense, cell wall lignification, cell wall β-glucan turnover, phytohormone activation, and release of aromatic compounds in plants, and biomass conversion in microorganisms. These functions lead to many agricultural and industrial applications. β-Glucosidases have been classified into glycoside hydrolase (GH) families GH1, GH3, GH5, GH9, and GH30, based on their amino acid sequences, while other β-glucosidases remain to be classified. The GH1, GH5, and GH30 β-glucosidases fall in GH Clan A, which consists of proteins with (β/α)(8)-barrel structures. In contrast, the active site of GH3 enzymes comprises two domains, while GH9 enzymes have (α/α)(6) barrel structures. The mechanism by which GH1 enzymes recognize and hydrolyze substrates with different specificities remains an area of intense study.

Recent Developments in Glycoside Synthesis with Glycosynthases and Thioglycoligases

Glycosynthases are hydrolytically incompetent engineered glycosidases that catalyze the high-yielding synthesis of glycoconjugates from glycosyl fluoride donor substrates and appropriate acceptors. Glycosynthases from more than 10 glycoside hydrolase families have now been generated, allowing the synthesis of a wide range of oligosaccharides. Recent examples include glycosynthase-mediated syntheses of xylo-oligosaccharides, xyloglucans, glycolipids, and aryl glycosides. Glycosynthases have also now been generated from inverting glycosidases, increasing the range of enzyme scaffolds. Improvement of glycosynthase activity and broadening of specificity has been achieved through directed evolution approaches, and several novel high-throughput screens have been developed to allow this. Finally, metabolically stable glycoside analogues have been generated using another class of mutant glycosidases: thioglycoligases. Recent developments in all these aspects are discussed.

The Chitopentaose Complex of a Mutant Hen Egg-White Lysozyme Displays No Distortion of the –1 Sugar Away from a 4C1 Chair Conformation

Glycosidase inhibitors frequently reflect either the charge or the ‘flattened’ shape of the oxocarbenium-ion like transition state. Much of the impetus for such inhibitory strategies derives from historical studies on ligand binding to hen egg white lysozyme (HEWL); not least those suggesting that product complexes of the enzyme showed distortion of the pyranosides in the –1 subsite. Ironically, while distortion is undoubtedly a defining feature of glycosidases, product complexes themselves are rarely distorted. Here we show that the chitopentaose product complex of a mutant E35Q HEWL, solved at 1.8 Å resolution, is bound with all sugars in 4C1 conformation.

Improved catalytic efficiency of endo-beta-1,4-glucanase from Bacillus subtilis BME-15 by directed evolution

Bacillus subtilis endo-beta-1,4-glucanase (Cel5A) hydrolyzes cellulose by cleavage of the internal bonds in the glucose chains, producing new ends randomly. Using directed evolution techniques of error-prone polymerase chain reaction (PCR) and DNA shuffling, several Cel5A variants with improved catalytic activity had been screened from the mutant library, which contained 71,000 colonies. Compared with the wild-type enzyme, the variants (M44-11, S75 and S78) showed 2.03 to 2.68-fold increased activities toward sodium carboxymethyl cellulose (CMC), while the M44-11 also exhibited a wider pH tolerance and higher thermostability. Structural models of M44-11, S75, S78, and WT proteins revealed that most of the substitutions were not located in the strictly conserved regions, except the mutation V255A of S75, which was closed to the nucleophile Glu257 in the catalytic center of the enzyme. Moreover, V74A and D272G of M44-11, which were not located in the substrate binding sites and the catalytic center, might result in improved stability and catalytic activity. These results provided useful references for directed evolution of the enzymes that belonged to the glycoside hydrolase family 5 (GH5).

Teaching old enzymes new tricks: engineering and evolution of glycosidases and glycosyl transferases for improved glycoside synthesis

The therapeutic potential of glycosides has made them an attractive target for drug development. The biological extraction and chemical synthesis of these molecules is often challenging and low yielding, thus alternative methods for the synthesis of polysaccharides are being pursued. A new class of enzymes, glycosynthases, which are nucleophile mutants of glycosidases, can perform the transglycosylation reaction without hydrolyzing the product, and thus provide a valuable resource for polysaccharide and glycan synthesis. Directed evolution of glycosynthases has expanded the repertoire of glycosidic linkages formed and the donors and acceptors (both sugar and nonsugar) that can be used by the glycosynthase. The application of new screening methods, such as FACS, to the directed evolution of glycosynthases will aid in the development of enzymes that are able to efficiently synthesize new, and therapeutically relevant glycosidic linkages.

A Gibbs free energy correlation for automated docking of carbohydrates

Thermodynamic information can be inferred from static atomic configurations. To model the thermodynamics of carbohydrate binding to proteins accurately, a large binding data set has been assembled from the literature. The data set contains information from 262 unique protein-carbohydrate crystal structures for which experimental binding information is known. Hydrogen atoms were added to the structures and training conformations were generated with the automated docking program AutoDock 3.06, resulting in a training set of 225,920 all-atom conformations. In all, 288 formulations of the AutoDock 3.0 free energy model were trained against the data set, testing each of four alternate methods of computing the van der Waals, solvation, and hydrogen-bonding energetic components. The van der Waals parameters from AutoDock 1 produced the lowest errors, and an entropic model derived from statistical mechanics produced the only models with five physically and statistically significant coefficients. Eight models predict the Gibbs free energy of binding with an error of less than 40% of the error of any similar models previously published.

The Crystal Structure of Human Cytosolic β-Glucosidase Unravels the Substrate Aglycone Specificity of a Family 1 Glycoside Hydrolase

Human cytosolic beta-glucosidase (hCBG) is a xenobiotic-metabolizing enzyme that hydrolyses certain flavonoid glucosides, with specificity depending on the aglycone moiety, the type of sugar and the linkage between them. In this study, the substrate preference of this enzyme was investigated by mutational analysis, X-ray crystallography and homology modelling. The crystal structure of hCBG was solved by the molecular replacement method and refined at 2.7 A resolution. The main-chain fold of the enzyme belongs to the (beta/alpha)(8) barrel structure, which is common to family 1 glycoside hydrolases. The active site is located at the bottom of a pocket (about 16 A deep) formed by large surface loops, surrounding the C termini of the barrel of beta-strands. As for all the clan of GH-A enzymes, the two catalytic glutamate residues are located on strand 4 (the acid/base Glu165) and on strand 7 (the nucleophile Glu373). Although many features of hCBG were shown to be very similar to previously described enzymes from this family, crucial differences were observed in the surface loops surrounding the aglycone binding site, and these are likely to strongly influence the substrate specificity. The positioning of a substrate molecule (quercetin-4'-glucoside) by homology modelling revealed that hydrophobic interactions dominate the binding of the aglycone moiety. In particular, Val168, Trp345, Phe225, Phe179, Phe334 and Phe433 were identified as likely to be important in determining substrate specificity in hCBG, and site-directed mutagenesis supported a key role for some of these residues.

Glycosidase Inhibition: An Assessment of the Binding of 18 Putative Transition-State Mimics

The inhibition of glycoside hydrolases, through transition-state mimicry, is important both as a probe of enzyme mechanism and in the continuing quest for new drugs, notably in the treatment of cancer, HIV, influenza, and diabetes. The high affinity with which these enzymes are known to bind the transition state provides a framework upon which to design potent inhibitors. Recent work [for example, Bülow, A. et al. J. Am. Chem. Soc. 2000, 122, 8567-8568; Zechel, D. L. et al. J. Am. Chem. Soc. 2003, 125, 14313-14323] has revealed quite confusing and counter-intuitive patterns of inhibition for a number of glycosidase inhibitors. Here we describe a synergistic approach for analysis of inhibitors with a single enzyme 'model system', the Thermotoga maritima family 1 beta-glucosidase, TmGH1. The pH dependence of enzyme activity and inhibition has been determined, structures of inhibitor complexes have been solved by X-ray crystallography, with data up to 1.65 A resolution, and isothermal titration calorimetry was used to establish the thermodynamic signature. This has allowed the characterization of 18 compounds, all putative transition-state mimics, in order to build an 'inhibition profile' that provides an insight into what governs binding. In contrast to our preconceptions, there is little correlation of inhibitor chemistry with the calorimetric dissection of thermodynamics. The ensemble of inhibitors shows strong enthalpy-entropy compensation, and the random distribution of similar inhibitors across the plot of DeltaH degrees a vs TDeltaS degrees a likely reflects the enormous contribution of solvation and desolvation effects on ligand binding.

Structural, Kinetic, and Thermodynamic Analysis of Glucoimidazole-Derived Glycosidase Inhibitors†,‡

Inhibition of glycosidases has great potential in the quest for highly potent and specific drugs to treat diseases such as diabetes, cancer, and viral infections. One of the most effective ways of designing such compounds is by mimicking the transition state. Here we describe the structural, kinetic, and thermodynamic dissection of binding of two glucoimidazole-derived compounds, which are among the most potent glycosidase inhibitors reported to date, with two family 1 beta-glycosidases. Provocatively, while inclusion of the phenethyl moiety improves binding by a factor of 20-80-fold, this does not appear to result from better noncovalent interactions with the enzyme; instead, improved affinity may be derived from significantly better entropic contributions to binding displayed by the phenethyl-substituted imidazole compound.

Substrate specificity of Aspergillus oryzae family 3 beta-glucosidase

Among glycoside hydrolases, beta-glucosidase plays a unique role in many physiological and biocatalytical processes that involve the beta-linked O-glycosyl bond of various oligomeric saccharides or glycosides. Structurally, the enzyme can be grouped into glycoside hydrolase family 1 and 3. Although the basic ("retaining, double-displacement") mechanism for the catalysis of family 3 beta-glucosidase has been established, in-depth understanding of its structure-function relationship, particularly the substrate specificity that is of great interest for developing the enzyme as a versatile biocatalyst, remains limited. To further probe the active site, we carried out a comparative study on a family 3 beta-glucosidase from Aspergillus oryzae with substrates and competitive inhibitors of different structures, in attempt to evaluate the site-specific spatial and chemical interactions between a pyranosyl substrate and the enzyme. Our results showed the enzyme having a strict stereochemical requirement (to accommodate beta-d-glucopyranose) for its "-1" active subsite, in contrast to its family 1 counterpart.

De novo design of alpha-amylase inhibitor: a small linear mimetic of macromolecular proteinaceous ligands

We report a low molecular weight inhibitor of alpha-amylases based on a linear peptidic scaffold designed de novo through the use of combinatorial chemistry. The inhibitory motif denoted PAMI (peptide amylase inhibitor) was selected by using L-peptide libraries and was fine-tuned by the introduction of unnatural modifications. PAMI specifically inhibits glycoside hydrolases of family 13. Its interaction with porcine pancreatic alpha-amylase was characterized by inhibition kinetics, fluorescence competition assays with natural alpha-amylase inhibitors, and isothermal titration calorimetry. We demonstrate that the critical amino acid residues in PAMI are shared with those in the macromolecular proteinaceous inhibitors that, however, bind to alpha-amylases through a spatially scattered set of intermolecular contacts. Thus, natural molecular evolution as well as combinatorial evolution selected the same alpha-amylase binding determinants for completely different spatial frameworks.

Enzymatic transglycosylation of xylose using a glycosynthase

The application of the hyperactive glycosynthase derived from Agrobacterium sp. beta-glucosidase (AbgE358G-2F6) to the synthesis of xylo-oligosaccharides by using alpha-D-xylopyranosyl fluoride as donor represents the first successful use of glycosynthase technology for xylosyl transfer. Transfer to p-nitrophenyl beta-D-glucopyranoside yields di- and trisaccharide products with beta-(1-->4) linkages in 63% and 35% yields, respectively. By contrast, transfer to p-nitrophenyl beta-D-xylopyranoside yielded the beta-(1-->3) linked disaccharide and beta-D-Xyl-(1-->4)-beta-D-Xyl-(1-->3)-beta-D-Xyl-pNP as major products in 42% and 30% yields, respectively. Transfer of xylose to beta-D-Xyl-(1-->4)-beta-D-Xyl-pNP yielded the beta-(1-->4) linked trisaccharide in 98% yield, thereby indicating that transfers to xylo-disaccharides occur with formation of beta-(1-->4) bonds. Xylosylation of carbamate-protected deoxyxylonojirimycin produced a mixture of di- and tri-'saccharide' products in modest yields.

Survey of the year 2004: literature on applications of isothermal titration calorimetry

The market for commercially available isothermal titration calorimeters continues to grow as new applications and methodologies are developed. Concomitantly the number of users (and abusers) increases dramatically, resulting in a steady increase in the number of publications in which isothermal titration calorimetry (ITC) plays a role. In the present review, we will focus on areas where ITC is making a significant contribution and will highlight some interesting applications of the technique. This overview of papers published in 2004 also discusses current issues of interest in the development of ITC as a tool of choice in the determination of the thermodynamics of molecular recognition and interaction.