Non-linear impacts of harmful algae blooms on the coastal tourism economy

Harmful algae blooms (HABs) occur in water bodies throughout the globe and can have multi-faceted impacts on tourism. However, little is known of the magnitude of economic losses to the tourism sector as a result of HABs. There is limited understanding of the empirical relationships between HAB intensity and duration, and the effects of this phenomenon on the tourism sector. This study is based in the state of Florida, USA, a notable sun, sand, and sea destination in the western hemisphere, where blooms of a marine harmful algae are a recurrent threat to coastal tourism. The empirical framework is based on a month and county-level panel database that combines sales by tourism-related businesses with observations from the official HAB surveillance system of the state of Florida. We use time and space fixed-effects regressions to estimate the loss in tourism revenue associated with one additional day of red tide. Results indicate that impacts of HABs on tourism do not follow a linear pattern with increasing HAB concentrations, but rather appear to follow an inverted-U pattern. In other words, higher concentrations of the HAB organism do not necessarily imply higher economic losses, suggesting that the impacts of HABs on tourism are not driven solely by the biophysical element of cell density. Rather, these impacts appear to be mediated and amplified by human dimensions. The loss to tourism-related businesses due to the 2018 Florida red tide bloom was estimated to be $2.7 billion USD, which implies that HABs and their impact on tourism can be considered as a potential 'billion-dollar' disaster.

Estimating the Cost of Production of Two Pentatomids and One Braconid for the Biocontrol of Spodoptera frugiperda (Lepidoptera: Noctuidae) in Maize Fields in Florida

The fall armyworm is a polyphagous lepidopteran pest that primarily feeds on valuable global crops like maize. Insecticides and transgenic crops have long been a primary option for fall armyworm control, despite growing concerns about transgenic crop resistance inheritance and the rate of insecticide resistance development. Global dissemination of the pest species has highlighted the need for more sustainable approaches to managing overwhelming populations both in their native range and newly introduced regions. As such, integrated pest management programs require more information on natural enemies of the species to make informed planning choices. In this study, we present a cost analysis of the production of three biocontrol agents of the fall armyworm over a year. This model is malleable and aimed towards small-scale growers who might benefit more from an augmentative release of natural enemies than a repetitive use of insecticides, especially since, though the benefits of using either are similar, the biological control option has a lower development cost and is more environmentally sustainable.

Evaluating the Impact of Employing Local Tax Collectors to Improve State-Level Licensing Program Outcomes in Florida

The improvement of public services is an important public policy objective, and several approaches have been proposed and implemented across all levels of government to achieve this goal. A recent policy in Florida (FL) fosters collaboration between local and state governments by allowing local tax collector (TC) offices to receive and support applications for the state's concealed weapons (CW) license program. We use 80,020 application records to estimate process improvements brought about by this policy. Our analysis shows that by using TCs, the time for the application to be processed was one third the time it needed via mail and about 3% at the regional office. The likelihood of errors in applications and supporting documents decreased significantly. The policy, therefore, has improved the effectiveness of the CW licensing service in FL. Similar initiatives can be adopted by government entities facing bottlenecks in permitting or licensing processes.

Fabrication and characterization of thin silicon solar cells produced by in-line spray coating

Orthophosphoric acid spray-coating: a feasible method for pn junction formation on thin c-Si cells with lower cost and environmental impact.

Does intensification improve the economic efficiency of dairy farms?

In recent decades, the dairy sector has shown a global tendency toward intensification. This structural change may have significant effects on farm efficiency and, consequently, on the economic results of the farms. The goal of this study was to offer an empirical analysis of the effect of intensification on dairy farming. To do this, we first classified a sample of dairy farms according to their level of intensification by using a cluster analysis. We then estimated independent stochastic cost frontiers for each group of farms to calculate their levels of efficiency. The methodology used in this study allowed for the presence of different technologies within a sample, which is a methodological issue frequently avoided in the agricultural economics literature. The empirical results showed that intensive farms were closer to their cost frontier than extensive ones, suggesting a positive relationship between intensification and efficiency.

NMR investigations of protein-carbohydrate interactions: insights into the topology of the bound conformation of a lactose isomer and beta-galactosyl xyloses to mistletoe lectin and galectin-1

A hallmark of oligosaccharides is their often limited spatial flexibility, allowing them to access a distinct set of conformers in solution. Viewing each individual or even the complete ensemble of conformations as potential binding partner(s) for lectins in protein-carbohydrate interactions, it is pertinent to address the question on the characteristics of bound state conformation(s) in solution. Also, it is possible that entering the lectin's binding site distorts the low-energy topology of a glycosidic linkage. As a step to delineate the strategy of ligand selection for galactosides, a common physiological docking point, we have performed a NMR study on two non-homologous lectins showing identical monosaccharide specificity. Thus, the conformation of lactose analogues bound to bovine heart galectin-1 and to mistletoe lectin in solution has been determined by transferred nuclear Overhauser effect measurements. It is demonstrated that the lectins select the syn conformation of lactose and various structural analogues (Galbeta(1-->4)Xyl, Galbeta(1-->3)Xyl, Galbeta(1-->2)Xyl, and Galbeta(1-->3)Glc) from the ensemble of presented conformations. No evidence for conformational distortion was obtained. Docking of the analogues to the modeled binding sites furnishes explanations, in structural terms, for exclusive recognition of the syn conformer despite the non-homologous design of the binding sites.

Towards defining the role of glycans as hardware in information storage and transfer: basic principles, experimental approaches and recent progress

The term 'code' in biological information transfer appears to be tightly and hitherto exclusively connected with the genetic code based on nucleotides and translated into functional activities via proteins. However, the recent appreciation of the enormous coding capacity of oligosaccharide chains of natural glycoconjugates has spurred to give heed to a new concept: versatile glycan assembly by the genetically encoded glycosyltransferases endows cells with a probably not yet fully catalogued array of meaningful messages. Enciphered by sugar receptors such as endogenous lectins the information of code words established by a series of covalently linked monosaccharides as letters for example guides correct intra- and intercellular routing of glycoproteins, modulates cell proliferation or migration and mediates cell adhesion. Evidently, the elucidation of the structural frameworks and the recognition strategies within the operation of the sugar code poses a fascinating conundrum. The far-reaching impact of this recognition mode on the level of cells, tissues and organs has fueled vigorous investigations to probe the subtleties of protein-carbohydrate interactions. This review presents information on the necessarily concerted approach using X-ray crystallography, molecular modeling, nuclear magnetic resonance spectroscopy, thermodynamic analysis and engineered ligands and receptors. This part of the treatise is flanked by exemplarily chosen insights made possible by these techniques.

Carrier protein-modulated presentation and recognition of an N-glycan: observations on the interactions of Man(8) glycoform of ribonuclease B with conglutinin

Conglutinin is a serum lectin of the innate immune system, which binds high mannose N-glycans when these are appropriately presented on proteins. Here we use the conglutinin-ribonuclease B (RNaseB)-recognition system as a model to investigate the structural basis of selective recognition of protein-bound oligosaccharides by this carbohydrate-binding receptor. Conglutinin shows little binding to the isolated RNaseB-Man(8 )glycoform, and no binding to Man(5-6) glycoforms. In contrast, when the protein moiety is reduced and denatured we observe that conglutinin binds strongly to the isolated RNaseB-Man(8) glycoform and weakly to the Man(5-6) glycoforms. These results are in accord with observations on the binding to the N-glycans in the absence of carrier protein. NMR analyses of native RNaseB-Man(8) and -Man(5-6) glycoforms reveal that the three-dimensional structure of the protein moiety is essentially identical to that of non-glycosylated RNase (RNaseA). Thus there are no perceptible differences between the RNase protein forms that could account for differential availability of the N-glycan for conglutinin-binding. After reduction and denaturation, the NMR spectrum became typical of a non-structured polypeptide, although the conformational preferences of the N-glycosidic linkage were unchanged, and most importantly, the Man(8 )oligosaccharide retained the average conformational behavior of the free oligosaccharide irrespective of the carrier protein fold. This conformational freedom is clearly not translated into full availability of the oligosaccharide for the carbohydrate-recognition protein. We propose, therefore, that the differing bioactivity of the N-glycan is a reflection of the existence of different geometries of presentation of the carbohydrate determinant in relation to the protein surface within the glycan:carrier protein ensemble.

Description of a monomeric prototype galectin from the lizard Podarcis hispanica

Galectins are a continuously expanding family of beta-galactoside-binding lectins present in a variety of evolutionarily divergent animal species. Here we report, for the first time, that expression of galectins extends to the reptilia lineage of lizards. Up to five lactose-binding proteins were isolated from the lizard Podarcis hispanica by affinity chromatography on asialofetuin-Sepharose. The main component, which is most abundantly expressed in skin, was purified from this tissue and further characterized. Under native conditions the protein behaved as a monomer with a molecular mass of 14,500 Da and an isoelectric point of 6.3. Based on sequence homology of the 58 N-terminal amino acid residues with galectins, and on its demonstrated galactoside-binding activity, this lectin we named LG-14 (from Lizard Galectin and 14 kDa) is classified as a new member of the galectin family. LG-14 falls into and strengthen the still thinly populated category of monomeric prototype galectins.

Conformational studies of the Man8 oligosaccharide on native ribonuclease B and on the reduced and denatured protein

Site-specific presentation of oligosaccharides in the context of carrier proteins can influence markedly their recognition by carbohydrate-binding proteins. On RNaseB, the Man5-9 N-glycans at Asn-34 are bound by the serum lectin conglutinin when the glycoprotein is reduced and denatured, but there is no binding to the N-glycans on the native form of RNaseB. The RNaseB Man8, which is a glycoform preferentially bound by conglutinin, is the subject of the present study. The conformational behavior of the protein-linked oligosaccharide Man8 is investigated on the native and on the reduced and denatured RNaseB, using a combination of NMR and theoretical calculations. Quantitative data on the NOESY crosspeaks have been obtained, thereby allowing the comparison of mobilities of homologous linkages within the glycan chain. Oligosaccharide conformations compatible with the NMR data have been explored by molecular modeling of the free oligosaccharide, using two different force fields (AMBER and SYBYL). There are some differences between the results produced by the two force fields, the AMBER simulations providing a better agreement with the experimental data. The results indicate that both on the native and on the reduced heat-denatured glycoprotein, the RNase Man8 oligosaccharide exhibits a conformational behavior very similar to that of the free oligosaccharide. However, this conformational freedom of the N-glcyan does not amount to full availability for carbohydrate-recognition proteins and enzymes.

Medicinal chemistry based on the sugar code: fundamentals of lectinology and experimental strategies with lectins as targets

Theoretical calculations reveal that oligosaccharides are second to no other class of biochemical oligomery in terms of coding capacity. As integral part of cellular glycoconjugates they can serve as recognitive units for receptors (lectins). Having first been detected in plants, lectins are present ubiquitously. Remarkably for this field, they serve as bacterial and viral adhesins. Following a description of these branches of lectinology to illustrate history, current status and potential for medicinal chemistry, we document that lectins are involved in a wide variety of biochemical processes including intra- and intercellular glycoconjugate trafficking, initiation of signal transduction affecting e. g. growth regulation and cell adhesion in animals. It is thus justified to compare crucial carbohydrate epitopes with the postal code ensuring correct mail routing and delivery. In view of the functional relevance of lectins the design of high-affinity reagents to occupy their carbohydrate recognition domains offers the perspective for an attractive source of new drugs. Their applications can be supposed to encompass the use as cell-type-selective determinant for targeted drug delivery and as blocking devices in anti-adhesion therapy during infections and inflammatory disease. To master the task of devising custom-made glycans/glycomimetics for this purpose, the individual enthalpic and entropic contributions in the molecular rendezvous between the sugar receptor under scrutiny and its ligand in the presence of solvent molecules undergoing positional rearrangements need to be understood and rationally exploited. As remunerative means to this end, cleverly orchestrated deployment of a panel of methods is essential. Concerning the carbohydrate ligand, its topological parameters and flexibility are assessed by the combination of computer-assisted molecular-mechanics and molecular-dynamics calculations and NMR-spectroscopic measurements. In the presence of the receptor, the latter technique will provide insights into conformational aspects of the bound ligand and into spatial vicinity of the ligand to distinct side chains of amino acids establishing the binding site in solution. Also in solution, the hydrogen-bonding pattern in the complex can be mapped with monodeoxy and monofluoro derivatives of the oligosaccharide. Together with X-ray crystallographic and microcalorimetric studies the limits of a feasible affinity enhancement can be systematically probed. With galactoside-binding lectins as instructive mo del, recent progress in this area of drug design will be documented, emphasizing the general applicability of the outlined interdisciplinary approach.

The 2.15 A crystal structure of CG-16, the developmentally regulated homodimeric chicken galectin

Differential developmental regulation of expression, fine-specificity differences in ligand recognition and disparate capacity for homodimerization are characteristics of the two currently known proto-type chicken galectins. The X-ray crystal structure of the first avian galectin, the homodimeric agglutinin from chicken liver (CG-16), has been solved in the absence of ligand in two crystal forms. Although the arrangement of lectin dimers in the two crystals is different, the structure of the monomers and their association into the extended beta-sandwich that characterises the dimer are virtually identical. The fold establishes a beta-sandwich motif composed of a five-stranded and a six-stranded beta-sheet evocative of proto-type mammalian galectins. The carbohydrate-binding site is occupied by six water molecules that take the place of the sugar in the complex. They help to stabilise in the absence of the ligand the spatial arrangement of the amino acid side-chains involved in sugar recognition. Docking of N-acetyllactosamine into the binding site reveals that three of these water molecules, which are in direct contact with the protein, occupy positions equivalent to the key sugar hydroxyl groups, namely the hydroxyls at positions 4 and 6 of the galactose unit and at position 3 of the N-acetylglucosamine unit. Crystallographic data are fully consistent with the binding features in solution previously derived from chemical mapping with deoxy, fluoro and O-methyl derivatives and laser photo-CIDNP (chemically induced dynamic nuclear polarisation) studies. The possible molecular basis for the monomeric character of the chicken intestinal galectin as well as potential mechanisms of oxidative inactivation by disulphide bridging are evaluated on the basis of the given structural information concerning the CG-16 dimer interface and the cysteine residues, respectively.

Rat liver contains age-regulated cytosolic 3-deoxy-D-glycero-D-galacto-non-2-ulopyranosonic acid (Kdn)

Kdn (3-deoxy-D-glycero-D-galacto-non-2-ulopyranosonic acid), a unique deaminated member of the sialic acid family, has emerged as a new building block of glycoconjugates from a wide variety of organisms, ranging from bacteria to mammals. In particular, the presence of Kdn has been demonstrated in different rat organs and tissues, but not in liver. Here we report on the detection and quantitation of Kdn in rat liver and on its variations with postnatal development and aging. We have previously established the optimal conditions for derivatization of Kdn with 1,2-diamino-4, 5-methylene-dioxybenzene (DMB), and detection by reverse-phase HPLC. Analysis of whole liver homogenates and different subcellular fractions reveals that Kdn is fundamentally present in the cytosolic fraction as nucleotide precursor. The expression of Kdn, Neu5Gc, and Neu5Ac changes unevenly with age. While the content of Neu5Ac, the major species, and Neu5Gc decreases to a different extent from newborn to old animals, Kdn content decreases from newborn to trace amounts in adult rats and increases again with aging. Thus, expression of Kdn, Neu5Gc, and Neu5Ac appears to be independently regulated.

Binding of mannose-6-phosphate and heparin by boar seminal plasma PSP-II, a member of the spermadhesin protein family

PSP-I/PSP-II, a heterodimer of glycosylated spermadhesins, is the major component of boar seminal plasma. Similarly to other spermadhesins, the PSP-II subunit is a lectin which displays heparin- and zona pellucida glycoprotein-binding activities. We have investigated the ligand binding capabilities of the heterodimer and the isolated subunits using several polysaccharides, glycoproteins, and phospholipids. PSP-II binds the sulfated polysaccharides heparin and fucoidan in a dose-dependent and seemingly-specific manner. In addition, PSP-II binds oligosaccharides containing exposed mannose-6-phosphate monoester groups and the binding is selectively inhibited by mannose-6-phosphate and glucose-6-phosphate. Inhibition experiments indicate that binding of PSP-II to sulfated polysaccharides and mannose-6-phosphate-containing oligosaccharides involves distinct but possibly overlapping binding sites. Heterodimer formation with PSP-I abolishes both the heparin and the mannose-6-phosphate binding capabilities, suggesting that the corresponding sites may be located at the dimer interface. Using the crystal structure of PSP-I/PSP-II heterodimer as a template, we have explored possible binding sites which satisfy the observed binding characteristics. In the proposed models, PSP-II Arg43 appears to play a pivotal role in both heparin- and mannose-6-phosphate-complexation as well as in heterodimer formation.

Different architecture of the combining site of the two chicken galectins revealed by chemical mapping studies with synthetic ligand derivatives

The detailed comparison of the carbohydrate-binding properties of related galectins from one organism can be facilitated by the application of an array of deliberately tailored methyl beta-lactoside derivatives. Focusing on chicken due to its expression of two galectins as a model for this approach, the combining-site architecture of the lectin from adult liver (CL-16) is apparently homologous to that previously observed for bovine galectin-1 (Solís, D., Jiménez-Barbero, J., Martín-Lomas, M., and Díaz-Mauriño, T. (1994) Eur. J. Biochem. 223, 107-114). Besides preservation of the key interactions and minor differences, the lectin from adult intestine (CL-14) is able to accommodate an axial HO-3 at the glucose moiety. Homology-based modeling enabled us to tentatively attribute the observed differences to a slightly different orientation of pivotal side chains in the binding pocket due to distinct substitutions of amino acid residues in the variable region within the carbohydrate-recognition domain. Thus, the results suggest overlapping but distinct ranges of potential ligands for the two chicken lectins and provide new information on their relationship to mammalian galectins. The described approach is suggested to be of relevance to design pharmaceuticals with enhanced selectivity to a certain member within a family of related lectins.

Glycosylated boar spermadhesin AWN-1 isoforms. Biological origin, structural characterization by lectin mapping, localization of O-glycosylation sites, and effect of glycosylation on ligand binding

Spermadhesin AWN-1 is a 133-residues boar sperm surface lectin with capability to bind different ligands, e.g. glycoproteins from zona pellucida (ZP), soybean trypsin inhibitor and heparin, and is involved in capacitation and binding of spermatozoa to the homologous zona pellucida. Here, we report the characterization of N- and O-glycosylated isoforms of AWN-1. Non-glycosylated AWN-1 is present in seminal plasma and on epididymal and ejaculated spermatozoa whereas its N- and O-glycosylated isoforms are only secretory products of the seminal vesicles. Lectin mapping indicated the presence of the glycosylated AWN-1 isoform mixture of both fucosylated and non-fucosylated N-glycans, and of two different classes of O-linked carbohydrate chains. These N- and O-linked oligosaccharide chains are neither sialylated nor contain terminal Gal beta (1-4)-GlcNAc sequences. Noteworthy, N- and O-glycosylation (either class) are mutually exclusive on the same protein molecule, indicating that each glycosylated AWN-1 molecule contains a single oligosaccharide chain. Peptide mapping was used to locate the N- and the O-glycosylation sites. Glycosylation of AWN-1 with either of the carbohydrate chain types greatly impaired the ability of the spermadhesin to bind biotinylated zona pellucida glycoproteins and soybean trypsin inhibitor, suggesting that the blocking effect may be due to steric hindrance of the ligand-binding pocket.

Probing hydrogen-bonding interactions of bovine heart galectin-1 and methyl beta-lactoside by use of engineered ligands

The binding of different synthetic monodeoxy, O-methyl and fluorodeoxy derivatives of methyl beta-lactoside to galectin-1 from bovine heart has been studied to probe the role of hydrogen bonding in the recognition and binding. The energetic contributions of the hydroxyl groups of methyl beta-lactoside directly involved in the interaction have been estimated and the nature of the protein residues involved has been predicted on the basis of the free energy data. Interpretations of the results have been sustained by molecular modeling of the three-dimensional structure of the sugars in solution. One side of the disaccharide molecule is not involved (HO-6 and HO-2') or only marginally involved (HO-3') in hydrogen bonding. Moreover, O-methylation at these positions causes an enhancement of the binding, suggesting favourable interactions of the methyl groups which may come into contact with hydrophobic residues at the periphery of the combining site. Hydrogen-bonding interactions are almost exclusively restricted to the other side of the molecule: the C-4' and C-6' hydroxyl groups act as donors of the strongest hydrogen bonds to charged groups of the lectin, while the C-3 hydroxyl group participates in a strong hydrogen bond with a neutral group. The results also suggest that the N-acetyl NH group in N-acetyllactosamine, as well as the hydroxyl group at position C-2 in methyl beta-lactoside, are involved in a polar interaction with neutral groups of the combining site. This hydrogen-bonding pattern contrasts markedly with that previously reported for the two galactose-specific Ricinus communis lectins. The recognition of different epitopes of the same basic structure underlies the differences in the oligosaccharide-binding specificities of galectin-1 and the R. communis lectins.

[The syndrome of renal and pulmonary vasculitis with positive neutrophil anticytoplasmic antibodies and antibasement membrane antibodies. A case report]

The authors present a case of Goodpasture's syndrome with necrotizing vasculitis of spleen and appendix. Serological examination shows antiglomerular basement membrane antibodies and antineutrophil cytoplasmic antibodies. The authors review the literature to establish if this or other similar cases can be considered a distinct disease entity. The authors also mention the laboratory methods that are currently being used to classify more precisely the vasculitides associated with glomerulonephritis.

Differential recognition by conglutinin and mannan-binding protein of N-glycans presented on neoglycolipids and glycoproteins with special reference to complement glycoprotein C3 and ribonuclease B

Conglutinin and mannan-binding protein are serum proteins that have similar carbohydrate binding specificities toward high mannose-type oligosaccharides, and yet only conglutinin binds the complement glycoprotein iC3b, which contains oligosaccharides of this type. In the present study, the interactions of conglutinin and mannan-binding protein were evaluated with the complement glycoprotein C3, including various physiologically derived fragments of this glycoprotein, and neoglycolipids prepared from oligosaccharides released from C3 and its isolated alpha and beta chains. Several conclusions can be drawn. First, the interaction of conglutinin is profoundly influenced by the state of the protein moiety of the alpha chain in the vicinity of the glycosylation site Asn-917. Second, the binding to the C3-derived glycoprotein iC3b appears to be exclusively mediated through the Man8 or Man9 oligosaccharide on the alpha chain; there is no evidence for other N-linked oligosaccharides on C3 that are uniquely bound by conglutinin. Third, although conglutinin shows a more restricted binding relative to mannan-binding protein toward the oligosaccharides free of protein, it has a broader binding pattern toward the oligosaccharides as presented on C3-derived glycoproteins. From these and additional observations with RNase B, which contains high mannose-type oligosaccharides at Asn-34, it is clear that the protein moieties of these glycoproteins markedly influence the presentation of the oligosaccharides such that biological specificity is mediated by the commonly occurring high mannose-type oligosaccharides in the context of specific carrier proteins.

Involvement of the glucose moiety in the molecular recognition of methyl beta-lactoside by ricin: synthesis, conformational analysis, and binding studies of different derivatives at the C-3 region

Syntheses of the 3-aminodeoxy (4), 3-deoxy-3-methyl (5), and 3-epi (6) derivatives of methyl beta-lactoside (1) have been achieved from 1 in a straightforward way, and their solution conformations in water and dimethyl sulfoxide analysed through molecular mechanics and dynamics calculations and nuclear magnetic resonance data. The overall shape of all the compounds studied is fairly similar and may be described by conformers included in a low energy region with phi = 15 +/- 45 degrees and psi = -25 +/- 30 degrees, that is ca. 5% of the total potential energy surface for the glycosidic linkages of the disaccharides. The binding of the different compounds to ricin, the galactose-specific toxin from Ricinus communis, has been investigated. The results confirm the involvement of the C-3 region in a nonpolar interaction with the protein at the periphery of the combining site.

Characterization of two glycosylated boar spermadhesins

Boar spermadhesins AQN-1, AQN-3 and AWN form a recently described protein family, synthesized by the sexual accessory glands, and become associated with the sperm head upon ejaculation. They contain 109-133 amino acid residues, two conserved disulphide bridges, are not glycosylated, and have 40-60% primary structure identity. These boar polypeptides are multifunctional proteins, which possess heparin-, serine-protease-inhibitor- and/or zona-pellucida-glycoprotein-binding capability and have, therefore, been implicated in sperm capacitation and sperm-oocyte attachment. AQN-2 (18-20 kDa), however, is unique among boar spermadhesins in that it is the only member of the family which is known to be glycosylated and which possesses weak zona-pellucida-binding but not seminal-plasma-inhibitor-binding ability. In this study we report the structural and functional characterization of the two glycoproteins contained in the AQN-2 fraction. One component is identical with PSP-I, a major porcine seminal plasma protein whose function has not yet been identified, while the second protein is a glycosylated isoform of AQN-3. Here we show that the inability of the glycosylated boar spermadhesins to bind seminal-plasma protease inhibitors as well as the weak binding of glycosylated AQN-3 to zona pellucida glycoproteins is due to the presence of the oligosacharide chain on a conserved asparagine residue. This indicates that modification of a spermadhesin polypeptide framework may serve to modulate its ligand-binding capabilities.

Hydrogen-bonding pattern of methyl beta-lactoside binding to the Ricinus communis lectins

The binding of O-methyl and fluorodeoxy derivatives of methyl beta-lactoside to the Ricinus communis toxin (RCA60) and agglutinin (RCA120) was studied in order to determine the donor/acceptor relationships of the hydrogen bonds between the hydroxyl groups of methyl beta-lactoside and the binding sites of the lectins. Free energy contributions of the hydrogen bonds at each position have been estimated from these data and from those previously reported for the monodeoxy derivatives [Rivera-Sagredo, A., Solís, D., Díaz-Mauriño, T., Jiménez-Barbero, J. & Martín-Lomas, M. (1991) Eur. J. Biochem. 197, 217-228; Rivera-Sagredo, A., Jiménez-Barbero, J., Martín-Lomas, M., Solís, D. & Díaz-Mauriño, T. (1992) Carbohydr. Res. 232, 207-226]. The nature of the groups of the lectins involved in hydrogen bonding has been predicted on the basis of the free energy data. Analysis of the results indicates that both the C-3' and C-4' hydroxyl groups act as hydrogen-bond donors to charged groups of both RCA60 and RCA120. The C-6' and probably also the C-2' hydroxyl groups participate both as donors and as acceptors of two hydrogen bonds with neutral groups of the lectins. And finally, the C-6 hydroxyl group possibly acts as a donor of a weak hydrogen bond to a neutral group in RCA60, but not in RCA120. The results provide a molecular basis to explain some features of the binding specificity of the lectins. Comparison of RCA60 binding data with the recently refined X-ray crystal structure of the RCA60-lactose complex shows similarities but also some discrepancies that can be attributed to the marked influence of the pH on the carbohydrate-lectin interaction.

Reduction of ricin toxicity without impairing the saccharide-binding properties by chemical modification of the carboxyl groups

The usefulness of ricin as a research tool is handicapped by its extremely biohazardous nature. In this work, ricin toxicity has been reduced by chemical modification of carboxyl groups using 1-ethyl-3(3-dimethylaminopropyl) carbodiimide and [14C]glycine methyl ester. The reaction was carried out in 8 M urea and in the presence of 0.1 M lactose to protect the groups involved in saccharide binding. Together with carboxyl groups, tyrosine residues were also modified. The maximum modification achieved was 13 carboxyl groups and 7 tyrosines per molecule (about 30% of total carboxyls and tyrosines). The modification did not alter substantially the strength and specificity of the carbohydrate-binding ability of the lectin, as observed by hemagglutination tests and by inhibition assays with different carbohydrate structures. However, the LD50 decreased 90-fold when the highest modification was achieved. Therefore, the modified lectin can be used more safely in the study of galactose-containing carbohydrates.

Does fibrinogen contain populations with different degree of sialylation?

The reactivity of the galactose specific lectin from Ricinus communis seeds, ricin, towards the fractions of fibrinogen separated by DEAE-cellulose chromatography and their isolated glycopeptides was studied. Ricin is known to differentiate oligosaccharide chains with different degree of sialylation. The results indicated that the fractionation of fibrinogen is not correlated with a different degree of sialylation of its oligosaccharide chains. The higher sialic acid content of the most acidic fraction correlates with a higher neutral sugar content due to the presence of highly glycosylated contaminants. The possibility that the heterogeneity in the degree of sialylation is only of intramolecular nature is discussed.

Studies of the molecular recognition of synthetic methyl beta-lactoside analogues by Ricinus communis agglutinin

The 2-, 3-, 6-, 2'-, 3'-, 4'-, and 6'-deoxy derivatives and the 3-O-methyl derivative of methyl beta-lactoside have been synthesised and their binding to the galactose-specific agglutinin from Ricinus communis (RCA-120) has been investigated. The results indicate that HO-3,4,6 of the beta-D-galactopyranose moiety are the key polar groups. The main difference from the closely related ricin lectin RCA-60 involves HO-6 of the D-glucopyranose moiety, which seems to contribute to the binding of the carbohydrate to RCA-60 but not to RCA-120.

Involvement of the lysine-binding sites of plasminogen on its interaction with concanavalin A

Two different interactions are involved in the binding of plasminogen to concanavalin A-Sepharose: both variants 1 and 2 interact with the lectin through the lysine-binding sites and, in addition, variant 1 binds to concanavalin A due to carbohydrate recognition. Both kinds of interactions were also observed in solution by analytical ultracentrifugation. The binding of Lys-plasminogen to concanavalin A via lysine-binding sites largely exceeds that of Glu-plasminogen, in accordance with the higher affinity for lysine of Lys-plasminogen. This fact can be applied to the separation of both forms of plasminogen in a single chromatographic step.

Fractionation of plasmic fibrin(ogen) digests by lectin affinity chromatography

A method for the fractionation of plasmic digests of both fibrinogen and fibrin was developed by taking advantage of the different chromatographic behaviour of fibrinogen and its fragments on immobilized concanavalin A and Lens culinaris agglutinin. Columns with different lectin concentration but with the same total lectin content were tested. Fragment E was retained on all the concanavalin A-Sepharose preparations while fragment D was mostly eluted in the unbound fraction. However, the binding of fragment DD depended on the lectin concentration of the gel. Thus, the percentage of fragment DD specifically bound to concanavalin A-Sepharose increased from 5-10% to 67% as the lectin density of the gel increased from 0.9 to 8.7 mg/ml gel. On the other hand, Lens culinaris agglutinin-Sepharose retained fibrinogen and high molecular weight fragments depending on the lectin concentration of the gel while neither fragment E nor fragment D were bound to any of the columns.