Elevation of S2-bound α1-acid glycoprotein is associated with chronic hepatitis C virus infection and hepatocellular carcinoma.

There is an urgent need for new high-quality markers for the early detection of hepatocellular carcinoma (HCC). Åström et al. suggested that S2-bound α1-acid glycoprotein (AGP) might be a promising marker. Consequently, we evaluated the predictive advantage of S2-bound AGP in the early detection of HCC. In a retrospective case-control study of patients chronically infected with hepatitis C virus (HCV) and treated with direct-acting antiviral agents (n = 93), we measured S2-bound AGP using the HepaCheC® ELISA kit (Glycobond AB, Linköping, SE) at the start of treatment, end of treatment and follow-up (maximum: 78 months). Patients were retrospectively propensity score matched (1:2). Thirty-one patients chronically infected with HCV developed HCC after a sustained virological response, while 62 did not. In addition, samples of patients with chronic hepatitis B virus infection, metabolic dysfunction-associated steatotic liver disease and HCC of different etiologies were analysed. S2-bound AGP elevation in HCC patients was confirmed. However, we did not observe a predictive advantage of S2-bound AGP for the early detection of HCC during treatment and follow-up. Interestingly, S2-bound AGP levels correlated with aspartate aminotransferase (ρ = .56, p = 9.5×10-15) and liver elastography (ρ = .67, p = 2.2×10-16). Of note, S2-bound AGP decreased in patients chronically infected with HCV after treatment-induced HCV clearance. Fucosylated S2-bound AGP levels were elevated in patients with chronic HCV and HCC. The potential role of S2-bound AGP as a novel tumour marker requires further investigation.

A wide scan of plasma proteins demonstrates thioredoxin reductase 1 as a potential new diagnostic biomarker for hepatocellular carcinoma.

BACKGROUND: Patients with liver cirrhosis are recommended ultrasonography screening for early detection of hepatocellular carcinoma to increase the chances of curative treatment. However, ultrasonography alone lacks in sensitivity. Adding plasma biomarkers may increase the detection rate. We performed a broad exploratory analysis to find new plasma proteins with potential applicability for HCC screening in patients with cirrhosis. METHODS: In a protein discovery cohort of 172 patients with cirrhosis or HCC, we screened for 481 proteins with suspension bead array or proximity extension assay. From these, 24 proteins were selected for further analysis in a protein verification cohort (n = 160), using ELISA, Luminex or an electrochemiluminescence platform. A cut-off model and a stepwise logistic regression model were used to find combinations of proteins with the best discriminatory performance between HCC and cirrhosis. RESULTS: Stepwise logistic regression revealed alpha-fetoprotein (AFP), decarboxy-prothrombin (DCP), thioredoxin reductase 1 (TXNRD1), and fibroblast growth factor 21 (FGF21) as the proteins with the best discriminatory performance between HCC and cirrhosis. Adding TXNRD1 to DCP and AFP increased the AUC from 0.844 to 0.878, and combining AFP, DCP and TXNRD1 with age and sex resulted in an AUC of 0.920. FGF21, however, did not further increase the performance when including age and sex. CONCLUSION: In the present study, TXNRD1 improves the sensitivity and specificity of AFP and DCP as HCC screening tools in patients with cirrhosis. We suggest that TXNRD1 should be validated in prospective settings as a new complementary HCC biomarker together with AFP and DCP.

Synthesis and biological evaluation of fucoidan-mimetic glycopolymers through cyanoxyl-mediated free-radical polymerization.

The sulfated marine polysaccharide fucoidan has been reported to have health benefits ranging from antivirus and anticancer properties to modulation of high blood pressure. Hence, they could enhance the biological function of materials for biomedical applications. However, the incorporation of fucoidan into biomaterials has been difficult, possibly due to its complex structure and lack of suitable functional groups for covalent anchoring to biomaterials. We have developed an approach for a rapid synthesis of fucoidan-mimetic glycopolymer chains through cyanoxyl-mediated free-radical polymerization, a method suitable for chain-end functionalizing and subsequent linkage to biomaterials. The resulting sulfated and nonsulfated methacrylamido α-L-fucoside glycopolymers' fucoidan-mimetic properties were studied in HSV-1 infection and platelet activation assays. The sulfated glycopolymer showed similar properties to natural fucoidan in inducing platelet activation and inhibiting HSV-1 binding and entry to cells, thus indicating successful syntheses of fucoidan-mimetic glycopolymers.

Production and characterization of a monomeric form and a single-site form of Aleuria aurantia lectin.

Lectins have widely been used in structural and functional studies of complex carbohydrates. They usually bind carbohydrates with relatively low affinity, but compensate for this by multivalency. This multivalent nature of lectins can sometimes produce unwanted reactions such as agglutination or precipitation of target glycoproteins, when using them in different biological and analytical assays. The mushroom lectin Aleuria aurantia binds to fucose-containing oligosaccharides. It is composed of two identical subunits, and each subunit contains five binding sites for fucose. In this study, two forms of recombinant AAL were produced using site-directed mutagenesis. A monomeric form of AAL was produced by exchanging Tyr6 with Arg6, and a single-site fragment of AAL was produced by insertion of an NdeI restriction enzyme cleavage site and a stop codon in the coding sequence. The AAL forms were expressed as His-tagged proteins in Escherichia coli and purified by affinity chromatography. Binding properties of the two AAL forms were performed using surface plasmon resonance, enzyme-linked lectin assay analyses and isothermal titration calorimetry. Both the monomeric AAL (mAAL) and the single-site AAL (S2-AAL) forms retained their capacity to bind fucosylated oligosaccharides. However, both constructs exhibited properties that differed from the intact recombinant AAL (rAAL). mAAL showed similar binding affinities to fucosylated oligosaccharides as rAAL, but had less hemagglutinating capacity. S2-AAL showed a lower binding affinity to fucosylated oligosaccharides and, in contrast to rAAL and mAAL, S2-AAL did not bind to sialylated fuco-oligosaccharides. The study shows that molecular engineering is a highly useful tool for producing lectins with more defined properties such as decreased valency and defined specificities and affinities. Thus, this approach has high potential in developing reliable diagnostic and biological assays for carbohydrate analysis.

New treatment for IgA nephropathy: enteric budesonide targeted to the ileocecal region ameliorates proteinuria.

BACKGROUND: Systemic corticosteroid treatment has been shown to exert some protection against renal deterioration in IgA nephropathy (IgAN) but is not commonly recommended for long-term use due to the well-known systemic side effects. In this study, we investigated the efficacy and safety of a new enteric formulation of the locally acting glucocorticoid budesonide (Nefecon®), designed to release the active compound in the ileocecal region. The primary objective was to evaluate the efficacy of targeted release budesonide on albuminuria. METHODS: Budesonide 8 mg/day was given to 16 patients with IgAN for 6 months, followed by a 3-month follow-up period. The efficacy was measured as change in 24-h urine albumin excretion, serum creatinine and estimated glomerular filtration rate (eGFR). RESULTS: The median relative reduction in urinary albumin excretion was 23% during the treatment period (interquartile range: -0.36 to -0.04, P = 0.04) with pretreatment values ranging from 0.3 to 6 g/24 h (median: 1.5 g/24 h). The median reduction in urine albumin peaked at 40% (interquartile range: -0.58 to -0.15) 2 months after treatment discontinuation. Serum creatinine was reduced by 6% (interquartile range: -0.12 to -0.02; P = 0.003), and eGFR [Modification of Diet in Renal Disease (MDRD)] increased ∼8% (interquartile range: 0.02-0.16, P = 0.003) during treatment. No major corticosteroid-related side effects were observed. CONCLUSIONS: In the present pilot study, enteric budesonide targeted to the ileocecal region had a significant effect on urine albumin excretion, accompanied by a minor reduction of serum creatinine and a modest increase of eGFR calculated by the MDRD equation, while eGFR calculated from Cockcroft-Gault equation and cystatin C was not changed. Enteric budesonide may represent a new treatment of IgAN warranting further investigation.

Sialic acid residues play a pivotal role in alpha(1)-acid glycoprotein (AGP)-induced generation of reactive oxygen species in chemotactic peptide pre-activated neutrophil granulocytes.

OBJECTIVE: We have recently shown that terminal sialic acid residues are essential for alpha(1)-acid glycoprotein (AGP)-induced Ca(2+) mobilization in neutrophils. The aim of the present study was to establish the importance of sialic acid residues on AGP in modulating human neutrophil functions, with emphasis on the generation of reactive oxygen species (ROS). MATERIALS AND METHODS: ROS were measured by luminol-enhanced chemiluminescence in isolated human neutrophils. RESULTS: We found that AGP did not provoke ROS generation in resting or L-selectin presensitized neutrophils. Moreover, AGP did not affect the N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced ROS generation, but it slightly suppressed opsonized zymosan-induced responses. However, when the neutrophils were prestimulated with fMLP, the subsequent addition of AGP provoked a marked ROS response. Dose-response studies and time studies revealed that the ROS generating capacity of AGP was highest at a concentration of 0.05 mg/ml and when given 3-10 min after addition of fMLP. A desialylated form of AGP or pretreatment of neutrophils with 3'- and 6'-sialyllactose caused a substantially lower ROS response in neutrophils prestimulated with fMLP. CONCLUSIONS: Our data show that AGP can stimulate a second ROS response in fMLP preactivated neutrophils and that terminal sialic acid residues on AGP play a crucial role in this regard.

alpha(1)-acid glycoprotein (AGP)-induced platelet shape change involves the Rho/Rho kinase signalling pathway.

alpha(1)-acid glycoprotein (AGP) is an acute-phase protein that contributes to inflammation processes. The role of AGP in platelet activation and thrombosis is, however, largely unknown. Therefore, we thoroughly investigated the effects of AGP on human platelets. Platelets were isolated from healthy volunteers and subsequently exposed to AGP. Platelet responses were monitored as change in light transmission, intracellular calcium concentration, light microscopy and protein phosphorylation by Western blot. We found that AGP induced platelet shape change independently of a second release of adenine nucleotides or thromboxane A(2), and that effect was abolished by endothelium-derived platelet inhibitors such as nitric oxide (NO) and adenosine. Furthermore, AGP triggered a minor calcium response and a pronounced Rho/Rho-kinase-dependent increase in Thr696 phosphorylation of myosin phosphatase target subunit 1 (MYPT1). Moreover, the Rho/Rho-kinase inhibitor Y-27632 significantly decreased the AGP-induced shape change. The results also showed that the AGP-elicited shape change was antagonised by pretreatment with low doses of collagen and thrombospondin-1. Our results describe a novel mechanism by which AGP stimulates platelet shape change via activation of the Rho/Rho-kinase signalling pathway. Physiological important platelet inhibitors, such as NO, completely counterbalance the effect of AGP. Hence, the present study indicates that AGP directly contributes to platelet activation, which in turn might have an impact in physiological haemostasis and/or pathological thrombosis.

Determination of Fucose Concentration in a Lectin-Based Displacement Microfluidic Assay.

We compare three different methods to quantify the monosaccharide fucose in solutions using the displacement of a large glycoprotein, lactoferrin. Two microfluidic analysis methods, namely fluorescence detection of (labeled) lactoferrin as it is displaced by unlabeled fucose and the displacement of (unlabeled) lactoferrin in SPR, provide fast responses and continuous data during the experiment, theoretically providing significant information regarding the interaction kinetics between the saccharide groups and binding sites. For comparison, we also performed a static displacement ELISA. The stationary binding site in all cases was immobilized S2-AAL, a monovalent polypeptide based on Aleuria aurantia lectin. Although all three assays showed a similar dynamic range, the microfluidic assays with fluorescent or SPR detection show an advantage in short analysis times. Furthermore, the microfluidic displacement assays provide a possibility to develop a one-step analytical platform.

Synthetic glycopolymers and natural fucoidans cause human platelet aggregation via PEAR1 and GPIbα.

Fucoidans are sulfated fucose-based polysaccharides that activate platelets and have pro- and anticoagulant effects; thus, they may have therapeutic value. In the present study, we show that 2 synthetic sulfated α-l-fucoside-pendant glycopolymers (with average monomeric units of 13 and 329) and natural fucoidans activate human platelets through a Src- and phosphatidylinositol 3-kinase (PI3K)-dependent and Syk-independent signaling cascade downstream of the platelet endothelial aggregation receptor 1 (PEAR1). Synthetic glycopolymers and natural fucoidan stimulate marked phosphorylation of PEAR1 and Akt, but not Syk. Platelet aggregation and Akt phosphorylation induced by natural fucoidan and synthetic glycopolymers are blocked by a monoclonal antibody to PEAR1. Direct binding of sulfated glycopolymers to epidermal like growth factor (EGF)-like repeat 13 of PEAR1 was shown by avidity-based extracellular protein interaction screen technology. In contrast, synthetic glycopolymers and natural fucoidans activate mouse platelets through a Src- and Syk-dependent pathway regulated by C-type lectin-like receptor 2 (CLEC-2) with only a minor role for PEAR1. Mouse platelets lacking the extracellular domain of GPIbα and human platelets treated with GPIbα-blocking antibodies display a reduced aggregation response to synthetic glycopolymers. We found that synthetic sulfated glycopolymers bind directly to GPIbα, substantiating that GPIbα facilitates the interaction of synthetic glycopolymers with CLEC-2 or PEAR1. Our results establish PEAR1 as the major signaling receptor for natural fucose-based polysaccharides and synthetic glycopolymers in human, but not in mouse, platelets. Sulfated α-l-fucoside-pendant glycopolymers are unique tools for further investigation of the physiological role of PEAR1 in platelets and beyond.

The acute-phase protein alpha 1-acid glycoprotein (AGP) induces rises in cytosolic Ca2+ in neutrophil granulocytes via sialic acid binding immunoglobulin-like lectins (siglecs).

We studied whether the acute-phase protein alpha1-acid glycoprotein (AGP) induces rises in [Ca2+]i in neutrophils and sought to identify the corresponding AGP receptor (or receptors). We found that AGP elicited a minimal rise in [Ca2+]i in Fura-2-loaded neutrophils, and this response was markedly enhanced by pretreatment with anti-L-selectin antibodies. (The EC50 value of the AGP-induced Ca2+ response was 9 microg/ml.) Activation of phospholipase-C, Src tyrosine kinases, and PI3 kinases proved to be essential for the AGP-mediated increase in [Ca2+]i, whereas the p38 MAPK and SYK signaling pathways were not involved. Furthermore, antibodies against sialic acid binding, immunoglobulin-like lectin 5 (Siglec-5) and oligosaccharide 3'-sialyl-lactose both antagonized the AGP-induced response and caused an immediate increase in [Ca2+]i in anti-L-selectin-treated neutrophils, which indicates a signaling capacity of Siglec-5. We used modified forms of AGP (treated with mild periodate or neuraminidase) to establish the importance of sialic acid residues. The modified forms of AGP caused a much smaller rise in [Ca2+]i than did unaltered AGP. Affinity chromatography confirmed that unchanged AGP, but not neuraminidase-treated AGP, bound to Siglec-5. Our report provides the first evidence for a signaling capacity by AGP through a defined receptor. Pre-engagement of L-selectin significantly enhanced this signaling capacity.

Fucoidan-Mimetic Glycopolymers as Tools for Studying Molecular and Cellular Responses in Human Blood Platelets.

The marine sulfated polysaccharide fucoidan displays superior ability to induce platelet aggregation compared to other sulfated polysaccharides. As such, it is an attractive tool for studying molecular and cellular responses in activated platelets. The heterogeneous structure, however, poses a problem in such applications. This study describes the synthesis of sulfated α-l-fucoside-pendant poly(methacryl amides) with homogeneous structures. By using both thiol-mediated chain transfer and reversible addition-fragmentation chain transfer polymerization techniques, glycopolymers with different chain lengths are obtained. These glycopolymers show platelet aggregation response and surface changes similar to those of fucoidan, and cause platelet activation through intracellular signaling as shown by extensive protein tyrosine phosphorylation. As the platelet activating properties of the glycopolymers strongly mimic those of fucoidan, this study concludes these fucoidan-mimetic glycopolymers are unique tools for studying molecular and cellular responses in human blood platelets.

Reverse lectin ELISA for detecting fucosylated forms of α1-acid glycoprotein associated with hepatocellular carcinoma.

Altered fucosylation of glycoproteins is associated with development of hepatocellular carcinoma (HCC). Lectins have been commonly used to assay changes in fucosylation of plasma glycoproteins. In the present study a recombinantly engineered form of the fucose binding lectin Aleuria aurantia (AAL) consisting of a single binding site for fucose (S2), was used to construct a reverse lectin ELISA method. Microtiter plates coated with the S2 lectin were used to capture glycoproteins from plasma samples followed by antibody detection of S2-bound fucosylated α1-acid glycoprotein (S2-bound AGP). The method was used to compare the level of S2-bound AGP in serum samples from a small cohort of patients with hepatitis, cirrhosis or HCC. Using the reverse S2 lectin ELISA it was shown that the levels of S2-bound AGP was significantly higher in HCC patients compared to non-cancer patients and that there was also a significant elevation of S2-bound AGP in HCC patients compared to cirrhosis patients. There was no correlation between the level of S2-bound AGP and total AGP concentration. The performance of S2-bound AGP in differentiating HCC from cirrhosis samples or hepatitis samples were compared to other markers. A combination of S2-bound AGP, α-fetoprotein and AGP concentration showed performances giving area under receiver operating curves of 0.87 and 0.95 respectively.

HPLC analysis of carbohydrate deficient transferrin isoforms isolated by the Axis-Shield %CDT method.

BACKGROUND: Carbohydrate-deficient transferrin (CDT) is elevated during prolonged overconsumption of alcohol and CDT is considered to be the most specific biochemical marker for alcohol overconsumption. However, an accurate method for analysing CDT is necessary because the test is frequently used for example in legal matters. METHODS: Patient serum samples were analysed with the Axis-Shield %CDT and eluates were pooled together. Transferrin was purified from the pool by affinity chromatography and further analysed with HPLC to determine the ratios of different transferrin isoforms. RESULTS: In the eluates using the Axis-Shield %CDT method, a substantial amount of trisialo transferrin was found, which is generally not considered a CDT isoform. CONCLUSIONS: The fact that trisialo transferrin is present may generate falsely elevated CDT results and it could at least partly explain the discrepancy between results of the Axis-Shield %CDT assay and HPLC in routine analysis.

Synthesis and anticancer properties of fucoidan-mimetic glycopolymer coated gold nanoparticles.

Gold nanoparticles coated with fucoidan-mimetic glycopolymers were synthesized that displayed good colloidal stability and promising anti-cancer properties. Fucoidan mimetic glycopolymers on their own were nontoxic, while glycopolymer coated gold nanoparticles displayed selective cytotoxicity to human colon cancer cell lines (HCT116) while it was non-toxic to mouse fibroblast cells (NIH3T3).

Analysis of glycoproteins in cell culture supernatants using a lectin immunosensor technique.

A method based on a surface plasmon resonance technique for detection of changes in concentration and glycosylation of proteins in cell culture supernatant is described. The method was used to analyze alpha(1)-acid glycoprotein (AGP) produced by a human hepatoma cell line (HepG2). Cell culture supernatant was injected to a BIACORE 2000 instrument and AGP was captured on the sensor chip by immobilized antibodies. The captured glycoprotein was then analyzed for content of carbohydrate epitopes using three different lectins, Aleuria aurantia lectin (AAL), Sambucus nigra agglutinin (SNA), and Triticum vulgaris agglutinin (wheat germ agglutinin, WGA). The method was used to analyze changes in concentration and glycosylation of AGP produced by HepG2 cells grown with or without three different cytokines, interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), and transforming growth factor beta-1 (TGF beta(1)). Using the described method it was shown that when HepG2 cells were grown in the presence of IL-6 both AGP concentration and fucosylation increased. When HepG2 cells instead were grown in the presence of TGF beta(1) AGP fucosylation increased whereas AGP concentration decreased.

Fucosylation of alpha1-acid glycoprotein (orosomucoid) compared with traditional biochemical markers of inflammation in recent onset rheumatoid arthritis.

BACKGROUND: Fucosylation of alpha1-acid glycoprotein (AGP, orosomucoid) has previously been found to be increased in patients with rheumatoid arthritis. Furthermore, the degree of fucosylation has been suggested to reflect disease activity. Therefore, we investigated the fucosylation of AGP in 131 patients (96 women and 35 men) with recent onset rheumatoid arthritis (RA). We compared the results with traditional biochemical markers of inflammation, i.e. plasma concentrations of AGP (P-AGP), and C-reactive protein (P-CRP). METHODS: AGP fucosylation measured with a novel lectin enzyme-linked immunosorbent assay (ELISA) was compared with a disease activity score (DAS28) and its components, and with P-AGP, and P-CRP at the time of diagnosis, and at a follow-up visit 1 year later. RESULTS: Both men and women with RA had increased AGP fucosylation compared to healthy individuals. We found a weak correlation between AGP fucosylation and DAS28 only in men. In men with initially increased AGP fucosylation, the level of fucosylation correlated with the change in DAS28 during the first year following diagnosis. CONCLUSION: We conclude that AGP fucosylation is not superior to traditional markers of disease activity in RA. However, AGP fucosylation may give some additional information to traditional biochemical markers on the disease progression in men.

Lectin affinity capillary electrophoresis in glycoform analysis applying the partial filling technique.

The study of protein glycosylation and its significance in biological interactions is a field of growing interest. This work demonstrates a lectin-based separation of protein glycoforms of alpha1-acid glycoprotein (AGP or orosomucoid) with capillary electrophoresis. Glycoform analysis was performed with a "partial filling technique" with the lectin Concanavalin A (Con A) as affinity ligand. Con A separated human AGP into two peaks; the first peak included AGP glycoforms without biantennary glycans, and the second peak represented the fraction that had one or more biantennary glycans. The applicability of the method was demonstrated with the analysis of AGP from clinical samples and AGP treated with N-glycosidase F. The AGP separation was also used as a reporter system to estimate the dissociation constant (KD) between Con A and a competing sugar.

Disialo-trisialo bridging of transferrin is due to increased branching and fucosylation of the carbohydrate moiety.

BACKGROUND: Carbohydrate deficient transferrin (CDT) is used for detection of alcohol abuse and follow-up. High performance liquid chromatography (HPLC) of transferrin glycoforms is highly specific for identification of alcohol abuse, but unresolved disialo- and trisialotransferrin glycoforms sometimes makes interpretation difficult. The cause of this phenomenon is unknown, cannot be explained by genetic variants of transferrin, but seems to be associated with liver disease. METHODS: Nineteen serum samples showing di-tri bridging when analyzed by HPLC were collected. Transferrin was purified by affinity chromatography, and N-linked oligosaccharides were released enzymatically. The N-glycans were further analyzed by high performance anion-exchange chromatography with pulsed amperometric detection and MALDI-TOF mass spectrometry. RESULTS: The HPLC-analysis showed three different types of glycoform patterns. The N-glycans from fifteen samples showed patterns with increased number of triantennary structures containing one or two fucose residues. One sample contained an increased amount of triantennary glycans without fucose. Three samples showed a glycosylation pattern similar to normal transferrin. CONCLUSIONS: The di-tri bridging phenomenon was associated with alterations in transferrin glycosylation in the majority of cases. Transferrin contained a higher extent of triantennary and often fucosylated N-linked oligosaccharides. These results may be important in future diagnostic approaches to liver diseases.

Elucidating the selectivity of recombinant forms of Aleuria aurantia lectin using weak affinity chromatography.

Aberrant glycosylation is connected to several pathological conditions and lectins are useful tools to characterize glycosylated biomarkers. The Aleuria aurantia lectin (AAL) is of special interest since it interacts with all types of fucosylated saccharides. AAL has been expressed in Escherichia coli as a fully functional recombinant protein. Engineered variants of AAL have been developed with the aim of creating monovalent lectins with more homogenous binding characteristics. Four different forms of AAL were studied in the present work: native AAL purified from A. aurantia mushrooms, recombinant AAL dimer, recombinant AAL monomer and recombinant AAL site 2 (S2-AAL). The affinities of these AAL forms toward a number of saccharides were determined with weak affinity chromatography (WAC). Disaccharides with fucose linked α1-3 to GlcNAc interacted with higher affinity compared to fucose linked α1-6 or α1-4 and the obtained dissociation constants (K(d)) were in the range of 10µM for all AAL forms. Tetra- and pentasaccharides with fucose in α1-2, α1-3 or α1-4 had K(d) values ranging from 0.1 to 7mM while a large α1-6 fucosylated oligosaccharide had a K(d) of about 20µM. The recombinant multivalent AAL forms and native AAL exhibited similar affinities toward all saccharides, but S2-AAL had a lower affinity especially regarding a sialic acid containing fucosylated saccharide. It was demonstrated that WAC is a valuable technique in determining the detailed binding profile of the lectins. Specific advantages with WAC include a low consumption of non-labeled saccharides, possibility to analyze mixtures and a simple procedure using standard HPLC equipment.

Detection of a high affinity binding site in recombinant Aleuria aurantia lectin.

Lectins are carbohydrate binding proteins that are involved in many recognition events at molecular and cellular levels. Lectin-oligosaccharide interactions are generally considered to be of weak affinity, however some mushroom lectins have unusually high binding affinity towards oligosaccharides with K (d) values in the micromolar range. This would make mushroom lectins ideal candidates to study protein-carbohydrate interactions. In the present study we investigated the properties of a recombinant form of the mushroom lectin Aleuria aurantia (AAL). AAL is a fucose-binding lectin composed of two identical 312-amino acid subunits. Each subunit contains five binding sites for fucose. We found that one of the binding sites in rAAL had unusually high affinities towards fucose and fucose-containing oligosaccharides with K (d) values in the nanomolar range. This site could bind to oligosaccharides with fucose linked alpha1-2, alpha1-3 or alpha1-4, but in contrast to the other binding sites in AAL it could not bind oligosaccharides with alpha1-6 linked fucose. This binding site is not detected in native AAL (nAAL) one possible explanation may be that this site is blocked with free fucose in nAAL. Recombinant AAL was produced in E. coli as a His-tagged protein, and purified in a one-step procedure. The resulting protein was analyzed by electrophoresis, enzyme-linked lectin assay and circular dichroism spectroscopy, and compared to nAAL. Binding properties were measured using tryptophan fluorescence and surface plasmon resonance. Removal of the His-tag did not alter the binding properties of recombinant AAL in the enzyme-linked lectin assay. Our study forms a basis for understanding the AAL-oligosaccharide interaction and for using molecular techniques to design lectins with novel specificities and high binding affinities towards oligosaccharides.