Primary structure of a Thomsen-Friedenreich-antigen-specific lectin, jacalin [Artocarpus integrifolia (jack fruit) agglutinin]. Evidence for the presence of an internal repeat

Effect of temperature and pH on the structure and stability of tumor-specific lectin jacalin and insights into the location of its tryptophan residues: CD, DSC and fluorescence studies

Jacalin, the jackfruit seed lectin, exhibits high specificity for the tumor-specific T-antigen and is used in various biomedical and biotechnological applications. Here, we report biophysical studies on the thermal unfolding of jacalin and the effect of pH and temperature on its secondary structure. Differential scanning calorimetric (DSC) studies revealed that native jacalin unfolds at ∼60 °C and that carbohydrate binding stabilizes the protein structure. Circular dichroism spectroscopic studies indicated that the secondary structure of jacalin remains mostly unaffected over pH 2.0-9.0, whereas considerable changes were observed in the tertiary structure. DSC experiments demonstrated that jacalin exhibits two overlapping transitions between pH 2 and 5, which could be attributed to dissociation of the tetrameric protein into subunits and their unfolding. Interestingly, only one transition between pH 6 and 9 was observed, suggesting that the subunit dissociation and unfolding occur simultaneously. While quenching of the protein intrinsic fluorescence by acrylamide increased significantly upon carbohydrate binding, quenching by succinimide is essentially unaffected. We attribute this difference to increased exposure of Trp-123 in the α-chain as it is involved in carbohydrate binding. Both acrylamide and succinimide gave biphasic Stern-Volmer plots, consistent with differential accessibility of the two tryptophan residues of jacalin to them.

Sub-Micellar Concentration of Sodium Dodecyl Sulphate Prevents Thermal Denaturation Induced Aggregation of Plant Lectin, Jacalin

The irreversible thermal unfolding of jacalin, the lectin purified from jackfruit seeds was accompanied by aggregation, where intermolecular interactions among the subunits are favoured over intramolecular interactions. The extent of aggregation increased as a function of temperature, time and protein concentration. The anionic surfactant, sodium dodecyl sulphate (SDS) significantly suppressed the formation of aggregates as observed by turbidity measurements and Rayleigh scattering assay. Moreover, far UV-CD spectra indicate that the protein β sheet transforms into α helical structure, when denatured in the presence of 3 mM SDS. Further, jacalin when heated in the presence of SDS partially retained the hemagglutination activity when jacalin-SDS mixture was diluted to 1:8 factor since 3 mM SDS was found to lyse the red blood cells. Thus, SDS only altered the aggregation behaviour of jacalin by preventing intermolecular hydrogen bonding among the exposed residues but did not completely stabilize the native conformation.

Spectroscopic investigation on the interaction of ruthenium complexes with tumor specific lectin, jacalin

Several ruthenium complexes are regarded as anticancer agents and considered as an alternative to the widely used platinum complexes. Owing to the preferential interaction of jacalin with tumor-associated T-antigen, we report the interaction of jacalin with four ruthenium complex namely, tris(1,10-phenanthroline)ruthenium(II)chloride, bis(1,10-phenanthroline)(N-[1,10]phenanthrolin-5-yl-pyrenylmethanimine)ruthenium(II)chloride, bis(1,10-phenanthroline)(dipyrido[3,2-a:2',3'-c]-phenazine)ruthenium(II)chloride, bis(1,10-phenanthroline)(11-(9-acridinyl)dipyrido[3,2-a:2',3'-c]phenazine)ruthenium(II) chloride. Fluorescence spectroscopic analysis revealed that the ruthenium complexes strongly quenched the intrinsic fluorescence of jacalin through a static quenching procedure, and a non-radiative energy transfer occurred within the molecules. Association constants obtained for the interaction of different ruthenium complexes with jacalin are in the order of 10(5) M(-1), which is in the same range as those obtained for the interaction of lectin with carbohydrate and hydrophobic ligand. Each subunit of the tetrameric jacalin binds one ruthenium complex, and the stoichiometry is found to be unaffected by the presence of the specific sugar, galactose. In addition, agglutination activity of jacalin is largely unaffected by the presence of the ruthenium complexes, indicating that the binding sites for the carbohydrate and the ruthenium complexes are different. These results suggest that the development of lectin-ruthenium complex conjugate would be feasible to target malignant cells in chemo-therapeutics.

Jacalin-carbohydrate interactions: distortion of the ligand molecule as a determinant of affinity

Jacalin is among the most thoroughly studied lectins. Its carbohydrate-binding site has also been well characterized. It has been postulated that the lower affinity of β-galactosides for jacalin compared with α-galactosides is caused by steric interactions of the substituents in the former with the protein. This issue has been explored energetically and structurally using different appropriate carbohydrate complexes of jacalin. It turns out that the earlier postulation is not correct. The interactions of the substituent with the binding site remain essentially the same irrespective of the anomeric nature of the substitution. This is achieved through a distortion of the sugar ring in β-galactosides. The difference in energy, and therefore in affinity, is caused by a distortion of the sugar ring in β-galactosides. The elucidation of this unprecedented distortion of the ligand as a strategy for modulating affinity is of general interest. The crystal structures also provide a rationale for the relative affinities of the different carbohydrate ligands for jacalin.

Comprehensive list of lectins: origins, natures, and carbohydrate specificities

More than 100 years have passed since the first lectin ricin was discovered. Since then, a wide variety of lectins (lect means "select" in Latin) have been isolated from plants, animals, fungi, bacteria, as well as viruses, and their structures and properties have been characterized. At present, as many as 48 protein scaffolds have been identified as functional lectins from the viewpoint of three-dimensional structures as described in this chapter. In this chapter, representative 53 lectins are selected, and their major properties that include hemagglutinating activity, mitogen activity, blood group specificity, molecular weight, metal requirement, and sugar specificities are summarized as a comprehensive table. The list will provide a practically useful, comprehensive list for not only experienced lectin users but also many other non-expert researchers, who are not familiar to lectins and, therefore, have no access to advanced lectin biotechnologies described in other chapters.

Deletion of the N-terminal dirigent domain in maize beta-glucosidase aggregating factor and its homolog sorghum lectin dramatically alters the sugar-specificities of their lectin domains

Maize beta-glucosidase aggregating factor (BGAF) and its homolog Sorghum Lectin (SL) are modular proteins consisting of an N-terminal dirigent domain and a C-terminal jacalin-related lectin (JRL) domain. BGAF is a polyspecific lectin with a monosaccharide preference for galactose, whereas SL displays preference for GalNAc. Here, we report that deletion of the N-terminal dirigent domain in the above lectins dramatically changes their sugar-specificities. Deletions in the N-terminal region of the dirigent domain of BGAF abolished binding to galactose/lactose, but binding to mannose was unaffected. Glucose, which was a poor inhibitor of hemagglutinating activity of BGAF, displayed higher inhibitory effect on the hemagglutinating activity of deletion mutants. Deletion of the dirigent domain in SL abolished binding to GalNAc, but binding to mannose was not affected. Surprisingly, fructose, an extremely poor inhibitor (minimum inhibitory concentration (MIC) = 125 mM) of SL hemagglutinating activity, was found to be a very potent inhibitor (MIC = 1 mM) of hemagglutinating activity of its JRL domain. These results indicate that the dirigent domain in this class of modular lectins, at least in the case of maize BGAF and SL, influences sugar specificity.

Artocarpus: a review of its traditional uses, phytochemistry and pharmacology

The genus Artocarpus (Moraceae) comprises about 50 species of evergreen and deciduous trees. Economically, the genus is of appreciable importance as a source of edible fruit, yield fairly good timber and is widely used in folk medicines. The aim of the present review is to present comprehensive information of the chemical constituents, biological and pharmacological research on Artocarpus which will be presented and critically evaluated. The close connection between traditional and modern sources for ethnopharmacological uses of Artocarpus species, especially for treatment against inflammation, malarial fever, diarrhoea, diabetes and tapeworm infection. Artocarpus species are rich in phenolic compounds including flavonoids, stilbenoids, arylbenzofurons and Jacalin, a lectin. The extracts and metabolites of Artocarpus particularly those from leaves, bark, stem and fruit possess several useful bioactive compounds and recently additional data are available on exploitation of these compounds in the various biological activities including antibacterial, antitubercular, antiviral, antifungal, antiplatelet, antiarthritic, tyrosinase inhibitory and cytotoxicity. Several pharmacological studies of the natural products from Artocarpus have conclusively established their mode of action in treatment of various diseases and other health benefits. Jacalin, a lectin present in seeds of this plant has a wide range of activities. Strong interdisciplinary programmes that incorporate conventional and new technologies will be critical for the future development of Artocarpus as a promising source of medicinal products. In the present review, attempts on the important findings have been made on identification; synthesis and bioactivity of metabolites present in Artocarpus which have been highlighted along with the current trends in research on Artocarpus.

Homolog of the maize beta-glucosidase aggregating factor from sorghum is a jacalin-related GalNAc-specific lectin but lacks protein aggregating activity

Recently, we identified the maize beta-glucosidase aggregating factor (BGAF) as a jacalin-related lectin (JRL) and showed that its lectin domain is responsible for beta-glucosidase aggregation. By searching for BGAF homologs in sorghum, we identified and obtained an EST clone and determined its complete sequence. The predicted protein had the same modular structure as maize BGAF, shared 67% sequence identity with it, and revealed the presence of two potential carbohydrate-binding sites (GG...ATYLQ, site I and GG...GVVLD, site II). Maize BGAF1 is the only lectin from a class of modular JRLs containing an N-terminal dirigent and a C-terminal JRL domain, whose sugar specificity and beta-glucosidase aggregating activity have been studied in detail. We purified to homogeneity a BGAF homolog designated as SL (Sorghum lectin) from sorghum and expressed its recombinant version in Escherichia coli. The native protein had a molecular mass of 32 kD and was monomeric. Both native and recombinant SL-agglutinated rabbit erythrocytes, and inhibition assays indicated that SL is a GalNAc-specific lectin. Exchanging the GG...GVVLD motif in SL with that of maize BGAF1 (GG...GIAVT) had no effect on GalNAc-binding, whereas binding to Man was abolished. Substitution of Thr(293) and Gln(296) in site I to corresponding residues (Val(294) and Asp(297)) of maize BGAF1 resulted in the loss of GalNAc-binding, indicating that site I is responsible for generating GalNAc specificity in SL. Gel-shift and pull-down assays after incubating SL with maize and sorghum beta-glucosidases showed no evidence of interaction nor were any SL-protein complexes detected in sorghum tissue extracts, suggesting that the sorghum homolog does not participate in protein-protein interactions.

Proteins that bind high-mannose sugars of the HIV envelope

A broad range of proteins bind high-mannose carbohydrates found on the surface of the envelope protein gp120 of the human immunodeficiency virus and thus interfere with the viral life cycle, providing a potential new way of controlling HIV infection. These proteins interact with the carbohydrate moieties in different ways. A group of them interacts as typical C-type lectins via a Ca2+ ion. Another group interacts with specific single, terminal sugars, without the help of a metal cation. A third group is involved in more intimate interactions, with multiple carbohydrate rings and no metal ion. Finally, there is a group of lectins for which the interaction mode has not yet been elucidated. This review summarizes, principally from a structural point of view, the current state of knowledge about these high-mannose binding proteins and their mode of sugar binding.

Studies on recombinant single chain Jacalin lectin reveal reduced affinity for saccharides despite normal folding like native Jacalin

Sugar binding studies, inactivation, unfolding, and refolding of native Jacalin (nJacalin) from Artocarpus integrifolia and recombinant single-chain Jacalin (rJacalin) expressed in Escherichia coli were studied by intrinsic fluorescence and thermal and chemical denaturation approaches. Interestingly, rJacalin does not undergo any proteolytic processing in an E. coli environment. It has 100fold less affinity for methyl-alpha-galactose (Ka: 2.48 x 10(2)) in comparison to nJacalin (Ka: 1.58 x 10(4)), and it also binds Thomsen-Friedenreich (TF) disaccharide (Galbeta1-3GalNAc) with less affinity. Overall sugar binding characteristics of rJacalin are qualitatively similar to that of nJacalin (Gal<MealphaGal<MealphaTFdisaccharide). Circular dichroism studies at near- and far-UV, thermal, and chemical denaturation studies reveal that the rJacalin behaves like nJacalin. Guanidine hydrochloride-induced denaturation, followed by renaturation, yielded total recovery of sugar binding activity of rJacalin in comparison to partial recovery for nJacalin. This signifies the minor changes in the refolding pathways between native and recombinant lectins. The stability of rJacalin is dramatically reduced in the extreme pH range unlike nJacalin. Both lectins do not bind 1-anilino-8-naphthalene sulfonic acid (ANS) in the pH range of 5 to 12 but they do in the pH range of 1-3. Solute quenching studies of the lectin using acrylamide, KI, and CsCl indicated that the tryptophan residues have full accessibility to the neutral quencher and poor accessibility to ionic quenchers. In summary, biophysical and biochemical studies on the native versus recombinant Jacalin suggest that post-translational modification, i.e., the processing of Jacalin into two chains is probably not a prerequisite for sugar binding but may be required for higher affinity.

The Antineoplastic Lectin of the Common Edible Mushroom (Agaricus bisporus) Has Two Binding Sites, Each Specific for a Different Configuration at a Single Epimeric Hydroxyl

The lectin from the common mushroom Agaricus bisporus, the most popular edible species in Western countries, has potent antiproliferative effects on human epithelial cancer cells, without any apparent cytotoxicity. This property confers to it an important therapeutic potential as an antineoplastic agent. The three-dimensional structure of the lectin was determined by x-ray diffraction. The protein is a tetramer with 222 symmetry, and each monomer presents a novel fold with two beta sheets connected by a helix-loop-helix motif. Selectivity was studied by examining the binding of four monosaccharides and seven disaccharides in two different crystal forms. The T-antigen disaccharide, Galbeta1-3GalNAc, mediator of the antiproliferative effects of the protein, binds at a shallow depression on the surface of the molecule. The binding of N-acetylgalactosamine overlaps with that moiety of the T antigen, but surprisingly, N-acetylglucosamine, which differs from N-acetylgalactosamine only in the configuration of epimeric hydroxyl 4, binds at a totally different site on the opposite side of the helix-loop-helix motif. The lectin thus has two distinct binding sites per monomer that recognize the different configuration of a single epimeric hydroxyl. The structure of the protein and its two carbohydrate-binding sites are described in detail in this study.

Structural basis for the energetics of jacalin-sugar interactions: promiscuity versus specificity

Jacalin, a tetrameric lectin, is one of the two lectins present in jackfruit (Artocarpus integrifolia) seeds. Its crystal structure revealed, for the first time, the occurrence of the beta-prism I fold in lectins. The structure led to the elucidation of the crucial role of a new N terminus generated by post-translational proteolysis for the lectin's specificity for galactose. Subsequent X-ray studies on other carbohydrate complexes showed that the extended binding site of jacalin consisted of, in addition to the primary binding site, a hydrophobic secondary site A composed of aromatic residues and a secondary site B involved mainly in water-bridges. A recent investigation involving surface plasmon resonance and the X-ray analysis of a methyl-alpha-mannose complex, had led to a suggestion of promiscuity in the lectin's sugar specificity. To explore this suggestion further, detailed isothermal titration calorimetric studies on the interaction of galactose (Gal), mannose (Man), glucose (Glc), Me-alpha-Gal, Me-alpha-Man, Me-alpha-Glc and other mono- and oligosaccharides of biological relevance and crystallographic studies on the jacalin-Me-alpha-Glc complex and a new form of the jacalin-Me-alpha-Man complex, have been carried out. The binding affinity of Me-alpha-Man is 20 times weaker than that of Me-alpha-Gal. The corresponding number is 27, when the binding affinities of Gal and Me-alpha-Gal, and those of Man and Me-alpha-Man are compared. Glucose (Glc) shows no measurable binding, while the binding affinity of Me-alpha-Glc is slightly less than that of Me-alpha-Man. The available crystal structures of jacalin-sugar complexes provide a convincing explanation for the energetics of binding in terms of interactions at the primary binding site and secondary site A. The other sugars used in calorimetric studies show no detectable binding to jacalin. These results and other available evidence suggest that jacalin is specific to O-glycans and its affinity to N-glycans is extremely weak or non-existent and therefore of limited value in processes involving biological recognition.

Structural Basis for the Carbohydrate Specificities of Artocarpin: Variation in the Length of a Loop as a Strategy for Generating Ligand Specificity

Artocarpin, a tetrameric lectin of molecular mass 65 kDa, is one of the two lectins extracted from the seeds of jackfruit. The structures of the complexes of artocarpin with mannotriose and mannopentose reported here, together with the structures of artocarpin and its complex with Me-alpha-mannose reported earlier, show that the lectin possesses a deep-seated binding site formed by three loops. The binding site can be considered as composed of two subsites; the primary site and the secondary site. Interactions at the primary site composed of two of the loops involve mainly hydrogen bonds, while those at the secondary site comprising the third loop are primarily van der Waals in nature. Mannotriose in its complex with the lectin interacts through all the three mannopyranosyl residues; mannopentose interacts with the protein using at least three of the five mannose residues. The complexes provide a structural explanation for the carbohydrate specificities of artocarpin. A detailed comparison with the sugar complexes of heltuba, the only other mannose-specific jacalin-like lectin with known three-dimensional structure in sugar-bound form, establishes the role of the sugar-binding loop constituting the secondary site, in conferring different specificities at the oligosaccharide level. This loop is four residues longer in artocarpin than in heltuba, providing an instance where variation in loop length is used as a strategy for generating carbohydrate specificity.

Structural basis of the carbohydrate specificities of jacalin: an X-ray and modeling study

The structures of the complexes of tetrameric jacalin with Gal, Me-alpha-GalNAc, Me-alpha-T-antigen, GalNAcbeta1-3Gal-alpha-O-Me and Galalpha1-6Glc (mellibiose) show that the sugar-binding site of jacalin has three components: the primary site, secondary site A, and secondary site B. In these structures and in the two structures reported earlier, Gal or GalNAc occupy the primary site with the anomeric carbon pointing towards secondary site A. The alpha-substituents, when present, interact, primarily hydrophobically, with secondary site A which has variable geometry. O-H..., centered pi and C-H...pi hydrogen bonds involving this site also exist. On the other hand, beta-substitution leads to severe steric clashes. Therefore, in complexes involving beta-linked disaccharides, the reducing sugar binds at the primary site with the non-reducing end located at secondary site B. The interactions at secondary site B are primarily through water bridges. Thus, the nature of the linkage determines the mode of the association of the sugar with jacalin. The interactions observed in the crystal structures and modeling based on them provide a satisfactory qualitative explanation of the available thermodynamic data on jacalin-carbohydrate interactions. They also lead to fresh insights into the nature of the binding of glycoproteins by jacalin.

Binding profile of Artocarpus integrifolia agglutinin (Jacalin)

Artocarpus integrifolia agglutinin (Jacalin) from the seeds of jack fruits has attracted considerable attention for its diverse biological activities and has been recognized as a Galbeta1-->3GalNAc (T) specific lectin. In previous studies, the information of its binding was limited to the inhibition results of monosaccharides and several T related disaccharides, but its interaction with other carbohydrate structural units occurring in natural glycans has not been characterized. For this reason, the binding profile of this lectin was studied by enzyme linked lectinosorbent assay (ELLSA) with our glycan/ligand collection. Among glycoproteins (gps) tested for binding, high density of multi-Galbeta1-->3GalNAcalpha1--> (mT(alpha)) and GalNAcalpha1-->Ser/Thr (mTn) containing gps reacted most avidly with Jacalin. As inhibitors expressed as nanograms yielding 50% inhibition, these mT(alpha) and mTn containing glycans were about 7.1 x 10(3), 4.0 x 10(5), and 7.8 x 10(5) times more potent than monomeric T(alpha), GalNAc, and Gal. Of the sugars tested and expressed as nanomoles for 50% inhibition, Tn containing peptides, T(alpha), and the human P blood group active disaccharide (P(alpha), GalNAcbeta1-->3Galalpha1-->) were the best and about 283 times more active than Gal. We conclude that the most potent ligands for this lectin are mTn, mT, and possibly P(alpha) glycotopes, while GalNAcbeta1-->4Galbeta1-->, GalNAcalpha1-->3Gal, GalNAcalpha1-->3GalNAc, and Galalpha1-->3Gal determinants were poor inhibitors. Thus, the overall binding profile of Jacalin can be defined in decreasing order as high density of mTn, and mT(alpha) >>> simple Tn cluster > monomeric T(alpha) > monomeric P(alpha) > monomeric Tn > monomeric T > GalNAc > Gal > Methylalpha1-->Man z.Gt; Man and Glc (inactive). Our finding should aid in the selection of this lectin for biological applications.

Galactose-binding lectin from the seeds of champedak (Artocarpus integer): sequences of its subunits and interactions with human serum O-glycosylated glycoproteins

Our group has previously reported the isolation, partial characterisation, and application of a Galbeta1-3GalNAc- and IgA1-reactive lectin from the seeds of champedak (Artocarpus integer). In the present study, we have subjected the purified lectin to reverse-phase high performance liquid chromatography and sequenced its subunits. Determination of the N-terminal sequence of the first 47 residues of the large subunit demonstrated at least 95% homology to the N-terminal sequence of the alpha chains of a few other galactose-binding Artocarpus lectins. The two smaller subunits of the lectin, each comprised of 21 amino acid residues, demonstrated minor sequence variability. Their sequences were generally comparable to the beta chains of the other galactose-binding Artocarpus lectins. When used to probe human serum glycopeptides that were separated by two-dimensional gel electrophoresis, the lectin demonstrated strong apparent interactions with glycopeptides of IgA1, hemopexin, alpha2-HS glycoprotein, alpha1-antichymotrypsin, and a few unknown glycoproteins. Immobilisation of the lectin to Sepharose generated an affinity column that may be used to isolate the O-glycosylated serum glycoproteins.

The primary structure of the acidic lectin from winged bean (Psophocarpus tetragonolobus): insights in carbohydrate recognition, adenine binding and quaternary association

The amino acid sequence of the winged bean acidic lectin (WBA II) was determined by chemical means and by recombinant techniques. From the N- and C-terminal sequence, obtained chemically, primers were designed for PCR amplification of the genomic DNA. The PCR product was cloned and sequenced to get the complete primary structure of WBA II. Peptide fragments for sequencing were also obtained by tryptic cleavages of the native lectin. The WBA II sequence showed a high degree of homology with that of WBA I and Erythrina corallodendron lectin (ECorL), especially in the regions involved in subunit association, where there is a very high conservation of residues. This perhaps implies the importance of this particular region in subunit interactions in this lectin. In addition, many of the residues, involved in carbohydrate binding in legume lectins, appear to be conserved in WBA II. The distinct differences in anomeric specificity observed amongst WBA I, WBA II, ECorL and peanut agglutinin (PNA) may be explained by subtle differences in sequence/structure of their D-loops. WBA II binds adenine quite strongly; a putative adenine binding sequence has been identified.

Jacalin: a jackfruit (Artocarpus heterophyllus) seed-derived lectin of versatile applications in immunobiological research

Jacalin, the major protein from the jackfruit (Artocarpus heterophyllus) seeds, is a tetrameric two-chain lectin (molecular mass 65 kDa) combining a heavy alpha chain of 133 amino acid residues with a light beta chain of 20-21 amino acid residues. It is highly specific for the alpha-O-glycoside of the disaccharide Thomsen-Friedenreich antigen (Gal beta1-3GalNAc), even in its sialylated form. This property has made jacalin suitable for studying various O-linked glycoproteins, particularly human IgA1. Jacalin's uniqueness in being strongly mitogenic for human CD4+ T lymphocytes has made it a useful tool for the evaluation of the immune status of patients infected with human immunodeficiency virus (HIV)-1. The abundance of source material for the production of jacalin, its ease of purification, yield and stability have made it an attractive cost-effective lectin. It has found applications in diverse areas such as the isolation of human plasma glycoproteins (IgA1, C1-inhibitor, hemopexin, alpha2-HSG), the investigation of IgA-nephropathy, the analysis of O-linked glycoproteins and the detection of tumours.

Jacalin interacts with Asn-linked glycopeptides containing multi-antennary oligosaccharide structure with terminal alpha-linked galactose

The carbohydrate binding properties of jacalin lectin were examined using RAF9 cell-derived D-[6-3H]glucosamine-radiolabeled total glycopeptides containing N-linked and O-linked oligosaccharides. The binding of N-linked glycopeptides to jacalin was abolished by treatment of alpha-galactosidase whereas O-linked glycopeptides were still bound lectin after this treatment. The removal of O-linked oligosaccharides by mild alkaline/borohydride treatment completely eliminated the lectin binding of alpha-galactosidase treated glycopeptides. These results demonstrate that jacalin interacts with cellular glycopeptides containing N-linked oligosaccharides with terminal alpha-galactose residues as well as glycopeptides containing O-linked oligosaccharides.

A novel mode of carbohydrate recognition in jacalin, a Moraceae plant lectin with a beta-prism fold

Jacalin, a tetrameric two-chain lectin (66,000 Mr) from jackfruit seeds, is highly specific for the tumour associated T-antigenic disaccharide. The crystal structure of jacalin with methyl-alpha-D-galactose reveals that each subunit has a three-fold symmetric beta-prism fold made up of three four-stranded beta-sheets. The lectin exhibits a novel carbohydrate-binding site involving the N terminus of the alpha-chain which is generated through a post-translational modification involving proteolysis, the first known instance where such a modification has been used to confer carbohydrate specificity. This new lectin fold may be characteristic of the Moraceae plant family. The structure provides an explanation for the relative affinities of the lectin for galactose derivatives and provides insights into the structural basis of its T-antigen specificity.

Preparative isolation of the lectin jacalin by anion-exchange high-performance liquid chromatography

The lectin jacalin from Artocarpus integrifolia was purified to homogeneity in a single step by preparative anion-exchange high-performance liquid chromatography (HPLC). Selection of the optimum chromatographic parameters in gradient elution allowed a rapid procedure to be obtained for the qualitative and quantitative isolation of the most important alpha- and alpha'-jacalin components. A recovery of 27-33% was obtained from a total soluble extract using a polyacrylate-DEAE HPLC column. The identities of the two isolated polypeptides were established by N-terminal amino acid sequence analysis and from the IgA1 binding lectin activity.