Pseudomonas aeruginosa resistance of monosaccharide-functionalized glass surfaces.

Preventing microorganism colonization on a surface is a great challenge in the conception of medical, food and marine devices. Here, we describe the formation of carbohydrate functionalized glass surfaces with D-glucose, D-galactose and D-mannose and how they efficiently affected the bacterial attachment. The carbohydrate entities were covalently attached to the pre-functionalized surface by click chemistry thanks the copper catalysed alkyl-azide cycloaddition. Water contact angle and X-ray photoelectron spectroscopy characterisations showed a homogeneous and quantitative cycloaddition at the scale of microorganisms. The adhesion assays with Pseudomonas aeruginosa, used as model of opportunistic pathogen, indicated a significant diminution of almost 40% of the bacterial accumulation on glycosidic surfaces with respect to initial surface. This activity was further compared with a surface presenting a simple hydroxyl residue. Exploration of specific interactions through Lectin A deficient Pseudomonas aeruginosa mutant strain provided new evidences that Lectin A was involved in biofilm maturation, rather than bacterial attachment. Subsequently, the determination of surface free energy and the adhesion free energy between surfaces and bacterial cell wall showed that the adhesion was thermodynamically unfavourable.

Lectin-Functionalized Composite Hydrogels for "Capture-and-Killing" of Carbapenem-Resistant Pseudomonas aeruginosa.

Infections with multiresistant pathogens are a leading cause for mortality worldwide. Just recently, the World Health Organization (WHO) increased the threat rating for multiresistant Pseudomonas aeruginosa to the highest possible level. With this background, it is crucial to develop novel materials and procedures in the fight against multiresistant pathogens. In this study, we present a novel antimicrobial material, which could find applications as a wound dressing or antimicrobial coating. Lectins are multivalent sugar-binding proteins, which can be found in a variety of plants and bacteria, where they are associated with biofilm formation. By immobilizing lectin B on a protein-based hydrogel surface, we provided the hydrogel with the ability to immobilize ("catch") pathogens upon contact. Furthermore, another hydrogel layer was added which inhibits biofilm formation and releases a highly potent antimicrobial peptide to eradicate microorganisms ("kill"). The composite hydrogel showed a high antimicrobial activity against the reference strain Pseudomonas aeruginosa PAO1 as well as against a carbapenem-resistant clinical isolate (multiresistant Gram-negative class 4) and may thus represent a novel material to develop a new type of antimicrobial wound dressings to prevent infections with this problematic pathogen of burn or other large wounds.

Lectin-mediated reversible immobilization of human cells into a glycosylated macroporous protein hydrogel as a cell culture matrix.

3D cell culture is a helpful approach to study cell-cell interaction in a native-like environment, but is often limited due the challenge of retrieving cells from the material. In this study, we present the use of recombinant lectin B, a sugar-binding protein with four binding cavities, to enable reversible cell integration into a macroporous protein hydrogel matrix. By functionalizing hydrogel precursors with saccharose, lectin B can both bind to sugar moieties on the cellular surface as well as to the modified hydrogel network. Confocal microscopy and flow cytometry analysis revealed cells to be integrated into the network and to adhere and proliferate. Furthermore, the specificity and reversibility was investigated by using a recombinantly produced yellow fluorescent - lectin B fusion protein and a variety of sugars with diverging affinities for lectin B at different concentrations and elution times. Cells could be eluted within minutes by addition of L-fucose to the cell-loaded hydrogels to make cells available for further analysis.

Structures of two lectins from the roots of pokeweed (Phytolacca americana).

Pokeweed lectin (PL), a lectin specific for N-acetylglucosamine-containing saccharides, stimulates peripheral lymphocytes to undergo mitosis by binding to their cell surfaces. Four types of lectins have been isolated from the roots of pokeweed (Phytolacca americana) and shown to contain homologous domains but to have different molecular sizes and biological properties. PL-D, the smallest lectin in the group, has two isolectins, PL-D1 and PL-D2. PL-D1 consists of 84 amino-acid residues, while PL-D2 is identical to PL-D1 in sequence except for the lack of two C-terminal residues, Leu83 and Thr84. The crystal structures of PL-D1 and PL-D2 were solved by the molecular-replacement method and refined to 1.65 and 1.5 A resolution with R factors of 17.2 and 17.6%, respectively. The PL-Ds are composed of two repetitive chitin-binding domains, each of which has four S-S bridges and one putative carbohydrate-binding site. The two carbohydrate-binding sites in PL-D are located on one side of the molecule. The relative orientation of the two domains in PL-D1 differs from that in PL-D2. Two C-terminal residues of PL-D1 are invisible in the present crystal structure, indicating the flexibility of the region. PL-D2 has a Ca2+ ion bound to the C-terminus on the molecular surface. A wide distribution of acidic residues is characteristically observed on one side of the C-terminal region of PL-D.

Similarity between protein-protein and protein-carbohydrate interactions, revealed by two crystal structures of lectins from the roots of pokeweed.

The roots of pokeweed (Phytolacca americana) are known to contain the lectins designated PL-A, PL-B, PL-C, PL-D1, and PL-D2. Of these lectins, the crystal structures of two PLs, the ligand-free PL-C and the complex of PL-D2 with tri-N-acetylchitotriose, have been determined at 1.8A resolution. The polypeptide chains of PL-C and PL-D2 form three and two repetitive chitin-binding domains, respectively. In the crystal structure of the PL-D2 complex, one trisaccharide molecule is shared mainly between two neighboring molecules related to each other by a crystallographic 2(1)-screw axis, and infinite helical chains of complexed molecules are generated by the sharing of ligand molecules. The crystal structure of PL-C reveals that the molecule is a dimer of two identical subunits, whose polypeptide chains are located in a head-to-tail fashion by a molecular 2-fold axis. Three putative carbohydrate-binding sites in each subunit are located in the dimer interface. The dimerization of PL-C is performed through the hydrophobic interactions between the carbohydrate-binding sites of the opposite domains in the dimer, leading to a distinct dimerization mode from that of wheat-germ agglutinin. Three aromatic residues in each carbohydrate-binding site of PL-C are involved in the dimerization. These residues correspond to the residues that interact mainly with the trisaccharide in the PL-D2 complex and appear to mimic the saccharide residues in the complex. Consequently, the present structure of the PL-C dimer has no room for accommodating carbohydrate. The quaternary structure of PL-C formed through these putative carbohydrate-binding residues may lead to the lack of hemagglutinating activity.

Comparison of the in vitro antiproliferative effects of five immunosuppressive drugs on lymphocytes in whole blood from cats.

OBJECTIVE: To compare the in vitro immunosuppressive effects of cyclosporine and 4 novel immunosuppressive drugs on lymphocytes in whole blood collected from healthy cats. SAMPLE POPULATION: Whole blood samples collected from 10 healthy adult domestic shorthair cats. PROCEDURE: Mitogen-stimulated lymphocyte proliferation in whole blood incubated with and without various concentrations of cyclosporine, tacrolimus, sirolimus, mycophenolic acid (MPA), or A771726 was measured by use of [3H]thymidine incorporation. Drug concentrations that resulted in a 50% inhibition of mitogen-induced proliferation (IC50) were calculated. Lymphocyte viability was determined by use of the trypan blue dye exclusion method. RESULTS: An obvious dose-response relationship for the antiproliferative effects of each drug was detected. Mean IC50 determined with concanavalin A was 46 nM for cyclosporine, 9 nM for tacrolimus, 12 nM for sirolimus, 16 nM for MPA, and 30 mM for A771726, whereas with pokeweed mitogen, mean IC50 was 33 nM for cyclosporine, 5 nM for tacrolimus, 15 nM for sirolimus, 14 nM for mycophenolic acid, and 25 mM for A771726. Mitogen-stimulated and nonstimulated lymphocytes remained viable, regardless of drug evaluated. CONCLUSIONS AND CLINICAL RELEVANCE: Tacrolimus, sirolimus, MPA, and A771726 inhibited in vitro mitogen-stimulated proliferation of feline lymphocytes in a dose-dependent manner. These novel immunosuppressive drugs may be useful for management of immune-mediated inflammatory diseases and prevention and treatment of rejection in cats that undergo organ transplantation.

Amino acid sequence and some properties of lectin-D from the roots of pokeweed (Phytolacca americana).

Two pokeweed lectins, designated PL-D1 and PL-D2, have been isolated from the roots of pokeweed (Phytolacca americana) using chitin affinity column chromatography followed by gel filtration on a Sephacryl S-200 column and fast protein liquid chromatography on a Mono-Q column, and their amino acid sequences have been analyzed. PL-D1 consists of 84 amino acid residues and has a molecular mass of 9317, while PL-D2 has an identical sequence with PL-D1 except lack of the C-terminal Leu-Thr. PL-D is composed of two chitin-binding domains, A and B, with 50% homology with each other. Both PL-Ds did not agglutinate native rabbit erythrocytes, but showed about 0.1% of the agglutinating activity of wheat germ agglutinin toward trypsin-treated erythrocytes. In the presence of beta (1-->4) linked oligomers of N-acetyl-D-glucosamine, which inhibit the hemagglutination, PL-D1 had an ultraviolet-difference spectrum with maxima at 292-294 nm and 284-285 nm, attributed to the red shift of the tryptophan residue, suggesting the location of tryptophan residue(s) at or near saccharide-binding site of PL-D1.

Structural analysis of N-linked oligosaccharide of mitogenic lectin-B from the roots of pokeweed (Phytolacca americana).

The structure of an asparagine (N-) linked oligosaccharide of pokeweed lectin-B (PL-B) and the amino acid sequences around two glycosylation sites were identified. The pyridylamino (PA) oligosaccharide prepared from PL-B was eluted as a single peak on both reversed-phase (RP-) HPLC and size-fractionation (SF-) HPLC, and its structure was estimated to be Man alpha 1-->6(Man alpha 1-->3)(Xyl beta 1-->2) Man beta 1-->4GlcNAc beta 1-->4(Fuc alpha 1-->3)GlcNAc by a combination of component analysis, successive exoglycosidase digestions, IS-MS analysis, and 500 MHz 1H-NMR. Two tryptic glycopeptides were isolated from the reduced and S-pyridylethylated PL-B after gel filtration followed by RP-HPLC, indicating the presence of two glycosylation sites in PL-B. The amino acid sequences around the two glycosylation sites were determined to be Cys-Gly-Val-Asp-Phe-Gly-Asn(CHO)-Arg.

A high degree of sequence homology in the putative carbohydrate recognition domains of pokeweed mitogen and wheat germ agglutinin: poly-N-acetyllactosamine-binding lectins from different species.

The complete amino acid sequence of a poly-N-acetyllactosamine-binding pokeweed mitogen 4 (Pa-4) was determined using a protein sequencer. After digestion of Pa-4 with endoproteinase Lys-C, Asp-N, Arg-C or Glu-C, the resulting peptides were separated by reversed-phase high-performance liquid chromatography (HPLC) and then subjected to sequence analysis using a protein sequencer. The complete amino acid sequence of Pa-4 was found to exhibit a high degree of homology with that of wheat germ agglutinin (WGA) regarding their overall sequences and the spatial arrangement of cysteine-glycine. Furthermore, the amino acid residues of WGA directly involved in carbohydrate-binding sites were found in the homologous region in Pa-4. This is the first report to show that lectins from different plant families (Phytolaccaceae for Pa-4 and Gramineae for WGA) possess homologous primary sequences.

Purification and characterization of three mitogenic lectins from the roots of pokeweed (Phytolacca americana).

Three mitogenic lectins, designated PL-A, PL-B, and PL-C, were purified from the roots of pokeweed (Phytolacca americana) using Q-Sepharose column chromatography followed by gel filtration on Sephadex G-75, hydrophobic chromatography on Butyl-Toyopearl, and FPLC on a Mono-Q column. PL-A, PL-B, and PL-C are acidic proteins having isoelectric points of 4.35 and their apparent molecular masses were 22, 48, and 21 kDa by SDS-polyacrylamide gel electrophoresis in the presence of 2-mercaptoethanol, respectively. The three lectins have similar amino acid compositions rich in half-cystine and similar N-terminal sequences, indicating that they are homologous proteins. Identical sequences of N-terminal regions and six corresponding tryptic peptides in PL-A and PL-B suggested that PL-A may be an N-terminal half fragment of PL-B. Although all of three lectins have mitogenic activities, PL-B is a mitogenic lectin with the most potent hemagglutinating and mitogenic activities, and PL-C has almost no hemagglutinating activity.

Isolation and characterization of pokeweed mitogen-like phytomitogens from Shoriku, Phytolacca esculenta.

From saline extracts of Phytolacca esculenta (shoriku) roots, two phytomitogenes were isolated by salting out with (NH4),SO4 and chromatography on DEAE-cellulose and Sephadex G-100 columns. Both fractions were homogeneous on disc electrophoresis and on immunoelectrophoresis. One of these (Fraction E-2) was shown to be similar to pokeweed mitogen in respect to mol. wt (32,000) and amino acid composition. The other (Fraction E-3) was a protein of 18,000 mol. wt. Both fractions had similar biological activities to pokeweed mitogen in their ability to stimulate pig blood lymphocytes in vitro to incorporate tritiated thymidine, and to induce blastoid transformation. Both fractions contained an unusually large amount of cystine, i.e., 18 half-cystine residues % for Fraction E-2 and 22 residues % for Fraction E-3. Although these mitogens were resistant to deproteinizing procedures such as perchloric acid treatment and Sevag's procedure, the DNA synthesis-stimulating activity was inactivated by digestion with Pronase E and Nagarse, but resistant to trypsin, chymotrypsin, deoxyribonuclease, ribonuclease, lysozyme and neuraminidase. The activity was stable at acidic and neutral pH (4-7) but unstable at alkaline pH. The activity at pH 7.3 was stabilized by the addition of Ca2+ or Mg2+. On the addition of more than 2 mM of Ca2+, precipitation of mitogen occurred. From the above results the molecular basis of the mitogenic activity of shoriku mitogen is discussed.