Potato lectin: a three-domain glycoprotein with novel hydroxyproline-containing sequences and sequence similarities to wheat-germ agglutinin

Reusable glycan microarrays using a microwave assisted wet-erase (MAWE) process

Modern studies on binding of proteins to glycans commonly involve the use of synthetic glycans and their derivatives in which a small amount of the material is covalently printed onto a functionalized slide in a glycan microarray format. While incredibly useful to explore binding interactions with many types of samples, the common techniques involve drying the slides, which leads to irreversible association of the protein to the spots on slides to which they bound, thus limiting a microarray to a single use. We have developed a new technique which we term Microwave Assisted Wet-Erase (MAWE) glycan microarrays. In this approach we image the slides under wet conditions to acquire the data, after which the slides are cleaned of binding proteins by treatment with a denaturing SDS solution along with microwave treatment. Slides cleaned in this way can be reused multiple times, and an example here shows the reuse of a single array 15 times. We also demonstrate that this method can be used for a single-array per slide or multi-array per slide platforms. Importantly, the results obtained using this technique for a variety of lectins sequentially applied to a single array, are concordant to those obtained via the classical dry approaches on multiple slides. We also demonstrate that MAWE can be used for different types of samples, such as serum for antibody binding, and whole cells, such as yeast. This technique will greatly conserve precious glycans and prolong the use of existing and new glycan microarrays.

Structure-function and application of plant lectins in disease biology and immunity

Lectins are proteins with a high degree of stereospecificity to recognize various sugar structures and form reversible linkages upon interaction with glyco-conjugate complexes. These are abundantly found in plants, animals and many other species and are known to agglutinate various blood groups of erythrocytes. Further, due to the unique carbohydrate recognition property, lectins have been extensively used in many biological functions that make use of protein-carbohydrate recognition like detection, isolation and characterization of glycoconjugates, histochemistry of cells and tissues, tumor cell recognition and many more. In this review, we have summarized the immunomodulatory effects of plant lectins and their effects against diseases, including antimicrobial action. We found that many plant lectins mediate its microbicidal activity by triggering host immune responses that result in the release of several cytokines followed by activation of effector mechanism. Moreover, certain lectins also enhance the phagocytic activity of macrophages during microbial infections. Lectins along with heat killed microbes can act as vaccine to provide long term protection from deadly microbes. Hence, lectin based therapy can be used as a better substitute to fight microbial diseases efficiently in future.

A rapid and effective method for purification of a heat-resistant lectin from potato (Solanum tuberosum) tubers

The potato lectin has been identified to consist of two chitin-binding modules, each containing twin hevein domains. Based on the thermotolerance of the hevein polypeptide, a simple, rapid, and effective protocol for the small-scale purification of the potato lectin has been developed in this study. The method involves only one anion exchange chromatographic step beyond the ammonium sulfate precipitation and the heating treatment. With this method, the potato lectin, a glycoprotein with molecular mass of approximately 60 kDa was found and purified to homogeneity with 9513.3 u/mg of specific hemagglutination (HA) activity in 76.8% yield. The homogeneity was confirmed by SDS-PAGE electrophoresis and reverse-phase HPLC analysis. The purified lectin was identified using MS-based peptide sequencing (MALDI-TOF/TOF) and showed a 100% Confidence Interval as being homologous to hevein domains in potato lectin. The periodic acid-Schiff staining and ferric-orcinol assay for pentose, as well as its HA activity inhibition by chitosan oligomers further confirmed the purified lectin as a potato chitin-binding lectin. It is noteworthy that the purified potato lectin exhibited heat resistance, by which, together with a short time precipitation by ammonium sulfate, more than 96% of the total proteins in the crude extract were removed. The lectin therefore was easily resolved from the other remining proteins on a DEAE-methyl polyacrylate column.

Sugar-Binding Profiles of Chitin-Binding Lectins from the Hevein Family: A Comprehensive Study

Chitin-binding lectins form the hevein family in plants, which are defined by the presence of single or multiple structurally conserved GlcNAc (N-acetylglucosamine)-binding domains. Although they have been used as probes for chito-oligosaccharides, their detailed specificities remain to be investigated. In this study, we analyzed six chitin-binding lectins, DSA, LEL, PWM, STL, UDA, and WGA, by quantitative frontal affinity chromatography. Some novel features were evident: WGA showed almost comparable affinity for pyridylaminated chitotriose and chitotetraose, while LEL and UDA showed much weaker affinity, and DSA, PWM, and STL had no substantial affinity for the former. WGA showed selective affinity for hybrid-type N-glycans harboring a bisecting GlcNAc residue. UDA showed extensive binding to high-mannose type N-glycans, with affinity increasing with the number of Man residues. DSA showed the highest affinity for highly branched N-glycans consisting of type II LacNAc (N-acetyllactosamine). Further, multivalent features of these lectins were investigated by using glycoconjugate and lectin microarrays. The lectins showed substantial binding to immobilized LacNAc as well as chito-oligosaccharides, although the extents to which they bound varied among them. WGA showed strong binding to heavily sialylated glycoproteins. The above observations will help interpret lectin-glycoprotein interactions in histochemical studies and glyco-biomarker investigations.

Utility of pentose colorimetric assay for the purification of potato lectin, an arabinose-rich glycoprotein

Potato lectin (Solanum tuberosum agglutinin, STA) is an unusual glycoprotein containing approximately 50% carbohydrates by weight. Of the total carbohydrates, 92% is contributed by L: -arabinose, which are O-linked to hydroxyproline residues. The ferric chloride-orcinol assay (Bial's test), which is specific for pentoses has so far been used only for the determination of free pentoses in biological samples. However, this colorimetric assay has not been used for the detection of pentoses in bound form as it occurs in Solanaceae lectins (potato, tomato, and Datura lectins). Utilizing the pentose colorimetric assay for monitoring the presence of potato lectin, a simpler and shorter procedure for the purification of this lectin from potato tubers has been developed. The yield of potato lectin (1.73 mg per 100 g potato tuber) is twice compared to the yields reported in earlier procedures. Although potato lectin is well known for its specificity to free trimers and tetramers of N-acetyl-D: -glucosamine (GlcNAc), it possesses a similar specificity to the core (GlcNAc)(2) of N-linked glycoproteins. The utilization of the pentose assay in the purification of arabinose-rich lectins/agglutinins obviates the necessity for the use of agglutination assay in the various purification steps. The pentose assay appears to be a simple and convenient colorimetric assay for detecting any pentose-rich glycoprotein in plant extracts. The utility of the pentose assay appears to have a significant potential in the detection of hydroxyproline-rich glycoproteins (HRGPs), which are generally O-arabinosylated.

Insights into the anti-microbial defense of marine invertebrates: the penaeid shrimps and the oyster Crassostrea gigas

Research on innate immunity of the penaeid shrimps and the oyster Crassostrea gigas is motivated greatly by economical necessities. Indeed, the aquaculture of these organisms is now limited by the development of infectious diseases. Studying anti-microbial peptides/proteins (AMPs), which are effector molecules of the host defense, is particularly attractive not only for progressing basic knowledge on immunity but also because they offer various possible applications for disease management in aquaculture. AMPs are explored with a global approach,considering their structure, properties, function, gene expression, and tissue distribution during the response to infections. In shrimp, investigations of the penaeidins, which are constitutively expressed peptides, have highlighted the importance of hemocytes and hematopoiesis as major elements of the immune response, providing both local and systemic reactions. The activation of hematopoiesis must be regarded as a regulatory way for the expression and distribution of constitutively expressed immune effectors. As complementary approaches, genomics and gene profiling are promising to deepen our understanding of the anti-microbial defense of the oyster and the shrimp. However, real progress will depend also on the characterization of hemocyte lineages and hematopoiesis of these marine invertebrates as well as on the ontogenesis of their immune systems.

The tomato lectin consists of two homologous chitin-binding modules separated by an extensin-like linker

A cDNA encoding a putative lectin expressed in tomato leaves was identified and analysed. The lectin consists of two homologous chitin-binding modules interconnected by a short proline-rich domain containing a single Ser[Pro]( n ) repetitive motif. Each module comprises two in-tandem-arrayed hevein domains separated by a tetrapeptide linker. Besides the chitin-binding modules and proline-rich domain, the lectin contains two short unrelated domains located at the N- and C-termini of the protein respectively. Eventual elucidation of the molecular structure of the tomato lectin confirms the presumed chimaeric nature of the Solanaceae lectins but also indicates that all previously proposed models need to be revised.

Potato lectin: an updated model of a unique chimeric plant protein

A complete cDNA encoding a potato tuber lectin has been identified and sequenced. Based on the deduced amino acid sequence, the still enigmatic molecular structure of the classical chimeric potato lectin could eventually be determined. Basically, the potato lectin consists of two nearly identical chitin-binding modules, built up of two in-tandem arrayed hevein domains that are interconnected by an extensin-like domain of approximately 60 amino acid residues. Although this structure confirms the 'canonical' chimeric nature of the Solanaceae lectins, it differs fundamentally from all previously proposed models. The new insights in the structure are also discussed in view of the physiological role of the Solanaceae lectins.

Deglycosylation of glycoproteins with trifluoromethanesulphonic acid: elucidation of molecular structure and function

The alteration of proteins by post-translational modifications, including phosphorylation, sulphation, processing by proteolysis, lipid attachment and glycosylation, gives rise to a broad range of molecules that can have an identical underlying protein core. An understanding of glycosylation of proteins is important in clarifying the nature of the numerous variants observed and in determining the biological roles of these modifications. Deglycosylation with TFMS (trifluoromethanesulphonic acid) [Edge, Faltynek, Hof, Reichert, and Weber, (1981) Anal. Biochem. 118, 131-137] has been used extensively to remove carbohydrate from glycoproteins, while leaving the protein backbone intact. Glycosylated proteins from animals, plants, fungi and bacteria have been deglycosylated with TFMS, and the most extensively studied types of carbohydrate chains in mammals, the N-linked, O-linked and glycosaminoglycan chains, are all removed by this procedure. The method is based on the finding that linkages between sugars are sensitive to cleavage by TFMS, whereas the peptide bond is stable and is not broken, even with prolonged deglycosylation. The relative susceptibility of individual sugars in glycosidic linkage varies with the substituents at C-2 and the occurrence of amido and acetyl groups, but even the most stable sugars are removed under conditions that are sufficiently mild to prevent scission of peptide bonds. The post-translational modifications of proteins have been shown to be required for diverse biological functions, and selective procedures to remove these modifications play an important role in the elucidation of protein structure and function.

Characterization and sequence of tomato 2S seed albumin: a storage protein with sequence similarities to the fruit lectin

We found a 2S storage albumin from the seed of tomato ( Lycopersicon esculentum L. cv. Cherry) that cross-reacted with antiserum to the fruit lectin, and named it Lec2SA. According to its size and basicity, Lec2SA was classified into four isoforms. These isoforms have an M(r) of approximately 12,000, and are composed of a small subunit (M(r) 4,000) and a large subunit (M(r) 8,000) linked by disulfide bonds. The complete amino acid sequence of Lec2SA was determined. The small subunit was composed of 32 amino acids, whereas the large subunit contained 70 amino acids with a pyroglutamine as the N-terminal residue. The sequence of Lec2SA was similar to that of 2S albumins from different plants, such as Brazil nut and castor beans. Furthermore, a sequence similarity was found between the large subunit of Lec2SA and the peptide sequence from tomato lectin. Although these similarities were found, Lec2SA did not show hemagglutinating activity or sugar-chain-binding activity, indicating that Lec2SA lacks the carbohydrate-binding domain. These results suggest that tomato lectin is a chimeric lectin sharing the seed storage protein-like domain that is incorporated into the gene encoding tomato lectin through gene fusion.

Plant lectins: occurrence, biochemistry, functions and applications

Growing insights into the many roles of glycoconjugates in biorecognition as ligands for lectins indicates a need to compare plant and animal lectins. Furthermore, the popularity of plant lectins as laboratory tools for glycan detection and characterization is an incentive to start this review with a brief introduction to landmarks in the history of lectinology. Based on carbohydrate recognition by lectins, initially described for concanavalin A in 1936, the chemical nature of the ABH-blood group system was unraveled, which was a key factor in introducing the term lectin in 1954. How these versatile probes are produced in plants and how they are swiftly and efficiently purified are outlined, and insights into the diversity of plant lectin structures are also given. The current status of understanding their functions calls for dividing them into external activities, such as harmful effects on aggressors, and internal roles, for example in the transport and assembly of appropriate ligands, or in the targeting of enzymatic activities. As stated above, attention is given to intriguing parallels in structural/functional aspects of plant and animal lectins as well as to explaining caveats and concerns regarding their application in crop protection or in tumor therapy by immunomodulation. Integrating the research from these two lectin superfamilies, the concepts are discussed on the role of information-bearing glycan epitopes and functional consequences of lectin binding as translation of the sugar code (functional glycomics).

Classification of plant lectins in families of structurally and evolutionary related proteins

The majority of plant lectins can be classified in seven families of structurally and evolutionary related proteins. Within a given lectin family most but not necessarily all members are built up of protomers with a similar primary structure and overall 3-D fold. The overall structure of the native lectins is not only determined by the structure of the protomers but depends also on the degree of oligomerization and in some cases on the post-translational processing of the lectin precursors. In general, lectin families are fairly homogeneous for what concerns the overall specificity of the individual lectins, which illustrates that the 3-D structure of the binding site has been conserved during evolution. In the case of the jacalin-related lectins the occurrence of a mannose- and galactose-binding subfamily can be explained by the fact that a post-translational cleavage of the protomers (of the galactose-binding subfamily) yields a slightly altered binding site. Unlike the other families, the legume lectins display a wide range of specificites, which is clearly reflected in the occurrence of sugar-binding sites with a different 3-D structure.

A ZYGOTE-SPECIFIC PROTEIN WITH HYDROXYPROLINE-RICH GLYCOPROTEIN DOMAINS AND LECTIN-LIKE DOMAINS INVOLVED IN THE ASSEMBLY OF THE CELL WALL OF CHLAMYDOMONAS REINHARDTII (CHLOROPHYTA)

The cell wall of Chlamydomonas reinhardtii zygotes, which forms rapidly after the fusion of wall-free gametes, provides a tractable system for studying the properties and assembly of hydroxyproline-rich glycoproteins, the major proteinaceous components of green algal and plant cell walls. We report the cloning of the zsp2 gene and the analysis of its ZSP-2 product, a 58.9 kDa polypeptide that is synthesized exclusively by zygotes. The protein contains two (SP)_x repeats, establishing it as a member of the cell wall hydroxyproline-rich glycoproteins family. It also contains a 4-fold iteration of an amino acid sequence centered around cysteine residues, a configuration found in both plant and animal lectins. Furthermore, we report four observations on pellicle composition and production. First, cell-free preparations of the pellicle matrix are rich in hydroxyproline, arabinose, and galactose and contain bundles of very long fibrils. Second, glutathione blocks pellicle formation and results in the accumulation of long fibrils in the growth medium. Third, antibody to ZSP-2 also blocks pellicle formation. Fourth, ZSP-2 immunolocalizes to the boundary between the outer layers of the wall proper and the pellicle matrix. These observations are consistent with the possibility that the Cys-rich (glutathione-sensitive) lectin-like domains of ZSP-2 may bind to sugar residues on the long fibrils and anchor them to the cell wall, thereby initiating and maintaining pellicle formation.

A gene encoding a hevein-like protein from elderberry fruits is homologous to PR-4 and class V chitinase genes

We isolated SN-HLPf (Sambucus nigra hevein-like fruit protein), a hevein-like chitin-binding protein, from mature elderberry fruits. Cloning of the corresponding gene demonstrated that SN-HLPf is synthesized as a chimeric precursor consisting of an N-terminal chitin-binding domain corresponding to the mature elderberry protein and an unrelated C-terminal domain. Sequence comparisons indicated that the N-terminal domain of this precursor has high sequence similarity with the N-terminal domain of class I PR-4 (pathogenesis-related) proteins, whereas the C terminus is most closely related to that of class V chitinases. On the basis of these sequence homologies the gene encoding SN-HLPf can be considered a hybrid between a PR-4 and a class V chitinase gene.

Ultrastructural localisation and further biochemical characterisation of prolyl 4-hydroxylase from Phaseolus vulgaris: comparative analysis

Prolyl 4-hydroxylase (EC 1.14.11.2), the enzyme responsible for the post-translational hydroxylation of peptide proline, has been well described in animals but has been little studied in plants. The best characterised example is the enzyme from French bean (Phaseolus vulgaris). In this study, the biochemical properties of this plant enzyme were examined in more detail and, using specific polyclonal antibodies, the localisation of the enzyme was determined. Both alpha- and beta-subunits did not show multiple forms, suggesting a relatively broad specificity of the enzyme complex with respect to the target hydroxylated amino acid sequences. Antibodies to the mammalian and Chlamydomonas enzymes cross-react with the higher plant subunits, indicating that some epitopes are highly conserved. The P. vulgaris enzyme was inhibited by analogues of oxoglutarate, but was not susceptible to doxorubicin. Inhibition of the bean enzyme by an oxaloglycine derivative resulted in the retention of the target (hydroxy)proline-rich protein in the endomembrane system. Immunolocalisation of the enzyme showed close association with the endoplasmic reticulum and Golgi apparatus in root tip cells of P. vulgaris or Tropaeolum majus. This localisation was particularly pronounced in Golgi-associated vesicles of young root tip cells of T. majus, cell types where rapid synthesis and deposition of wall material was observed. These data are consistent with the hypothesis, proposed by Bolwell [G.P. Bolwell, Dynamic aspects of the plant extracellular matrix, Int. Rev. Cytol. 146 (1993) 261-324], that protein hydroxylation must be completed before the glycosylation of the target (hydroxy)proline-rich glycoproteins in the Golgi stack.