Lectin typing of methicillin-resistant Staphylococcus aureus

Glycomics Microarrays Reveal Differential In Situ Presentation of the Biofilm Polysaccharide Poly-N-acetylglucosamine on Acinetobacter baumannii and Staphylococcus aureus Cell Surfaces

The biofilm component poly-N-acetylglucosamine (PNAG) is an important virulence determinant in medical-device-related infections caused by ESKAPE group pathogens including Gram-positive Staphylococcus aureus and Gram-negative Acinetobacter baumannii. PNAG presentation on bacterial cell surfaces and its accessibility for host interactions are not fully understood. We employed a lectin microarray to examine PNAG surface presentation and interactions on methicillin-sensitive (MSSA) and methicillin-resistant S. aureus (MRSA) and a clinical A. baumannii isolate. Purified PNAG bound to wheatgerm agglutinin (WGA) and succinylated WGA (sWGA) lectins only. PNAG was the main accessible surface component on MSSA but was relatively inaccessible on the A. baumannii surface, where it modulated the presentation of other surface molecules. Carbohydrate microarrays demonstrated similar specificities of S. aureus and A. baumannii for their most intensely binding carbohydrates, including 3' and 6'sialyllactose, but differences in moderately binding ligands, including blood groups A and B. An N-acetylglucosamine-binding lectin function which binds to PNAG identified on the A. baumannii cell surface may contribute to biofilm structure and PNAG surface presentation on A. baumannii. Overall, these data indicated differences in PNAG presentation and accessibility for interactions on Gram-positive and Gram-negative cell surfaces which may play an important role in biofilm-mediated pathogenesis.

Differential recognition of Haemophilus influenzae whole bacterial cells and isolated lipooligosaccharides by galactose-specific lectins

Bacterial surfaces are decorated with carbohydrate structures that may serve as ligands for host receptors. Based on their ability to recognize specific sugar epitopes, plant lectins are extensively used for bacteria typing. We previously observed that the galactose-specific agglutinins from Ricinus communis (RCA) and Viscum album (VAA) exhibited differential binding to nontypeable Haemophilus influenzae (NTHi) clinical isolates, their binding being distinctly affected by truncation of the lipooligosaccharide (LOS). Here, we examined their binding to the structurally similar LOS molecules isolated from strains NTHi375 and RdKW20, using microarray binding assays, saturation transfer difference NMR, and molecular dynamics simulations. RCA bound the LOS_RdKW20 glycoform displaying terminal Galβ(1,4)Glcβ, whereas VAA recognized the Galα(1,4)Galβ(1,4)Glcβ epitope in LOS_NTHi375 but not in LOS_RdKW20, unveiling a different presentation. Binding assays to whole bacterial cells were consistent with LOS_NTHi375 serving as ligand for VAA, and also suggested recognition of the glycoprotein HMW1. Regarding RCA, comparable binding to NTHi375 and RdKW20 cells was observed. Interestingly, an increase in LOS_NTHi375 abundance or expression of HMW1 in RdKW20 impaired RCA binding. Overall, the results revealed that, besides the LOS, other carbohydrate structures on the bacterial surface serve as lectin ligands, and highlighted the impact of the specific display of cell surface components on lectin binding.

In vivo Release of Lectins from the Green Alga Ulva fasciata

The green alga Ulva fasciata Delile (Ulvaceae), after thawing from storage at −20oC, has been used to study the in vivo biosynthesis and release of lectins. The alga was made to resume viable growth by immersion in a PBS buffer, pH 7.4, containing 0.01% w/v sodium azide and irradiating with a halophosphate lamp. The growing alga readily took up 14C leucine, when this was added to the buffer, as seen by a decrease in a sample count rate of ~ 8000 cpm over a period of twenty minutes. The transfer of the radioactivity fed algae into fresh PBS buffer resulted in 14C labeled proteins being subsequently released into solution. As well as observing changes in levels of radioactivity, the release of proteins was also monitored by UV absorption at 280 nm. Both techniques indicated an initial steady release over the first twelve hours, followed by a slower approach to a plateau value. Transfer of the algae that had undergone an initial period of protein release into a subsequent second and third volume of fresh PBS buffer produced similar UV absorption profiles, but the total quantities of material released were reduced. Identification of the released proteins was obtained from their ability to agglutinate red blood cells, which was inhibited by L-fucose, and their electrophoretic mobilities when compared with earlier isolated samples of the U. fasciata lectin. The reference lectin was obtained by affinity chromatography, following the selective precipitation of the water soluble algal proteins with ammonium sulfate. We postulate that the observed release profiles support the previously suggested concept that lectins have the ability to function as protection agents for living marine algae.

Modulation of the pharmacological effects of enzymatically-active PLA2 by BTL-2, an isolectin isolated from the Bryothamnion triquetrum red alga

Background

An interaction between lectins from marine algae and PLA₂ from rattlesnake was suggested some years ago. We, herein, studied the effects elicited by a small isolectin (BTL-2), isolated from Bryothamnion triquetrum, on the pharmacological and biological activities of a PLA₂ isolated from rattlesnake venom (Crotalus durissus cascavella), to better understand the enzymatic and pharmacological mechanisms of the PLA₂ and its complex.

Results

This PLA₂ consisted of 122 amino acids (approximate molecular mass of 14 kDa), its pI was estimated to be 8.3, and its amino acid sequence shared a high degree of similarity with that of other neurotoxic and enzymatically-active PLA₂s. BTL-2 had a molecular mass estimated in approximately 9 kDa and was characterized as a basic protein. In addition, BTL-2 did not exhibit any enzymatic activity.

The PLA₂ and BTL-2 formed a stable heterodimer with a molecular mass of approximately 24–26 kDa, estimated by molecular exclusion HPLC. In the presence of BTL-2, we observed a significant increase in PLA₂ activity, 23% higher than that of PLA₂ alone. BTL-2 demonstrated an inhibition of 98% in the growth of the Gram-positive bacterial strain, Clavibacter michiganensis michiganensis (Cmm), but only 9.8% inhibition of the Gram-negative bacterial strain, Xanthomonas axonopodis pv passiflorae (Xap). PLA₂ decreased bacterial growth by 27.3% and 98.5% for Xap and Cmm, respectively, while incubating these two proteins with PLA₂-BTL-2 inhibited their growths by 36.2% for Xap and 98.5% for Cmm.

PLA₂ significantly induced platelet aggregation in washed platelets, whereas BTL-2 did not induce significant platelet aggregation in any assay. However, BTL-2 significantly inhibited platelet aggregation induced by PLA₂. In addition, PLA₂ exhibited strong oedematogenic activity, which was decreased in the presence of BTL-2. BTL-2 alone did not induce oedema and did not decrease or abolish the oedema induced by the 48/80 compound.

Conclusion

The unexpected results observed for the PLA₂-BTL-2 complex strongly suggest that the pharmacological activity of this PLA₂ is not solely dependent on the presence of enzymatic activity, and that other pharmacological regions may also be involved. In addition, we describe for the first time an interaction between two different molecules, which form a stable complex with significant changes in their original biological action. This opens new possibilities for understanding the function and action of crude venom, an extremely complex mixture of different molecules.

Lectin typing of five medically important Candida species

This study reports the patterns of agglutination of 93 clinical Candida isolates by 14 commercial lectins. The isolates were of the species Candida albicans (55), C. tropicalis (12), C. guilliermondii (10). C. glabrata (eight) and C. parapsilosis (eight). Hundred percent of isolates were agglutinated, at least, by a panel of three lectins: Canavalia ensiformis (ConA), Lens culinaris (LCA) and Pisum sativum (PSA), all of them with alpha-D-mannose specificity. In addition, another panel of three lectins could distinguish between C. glabrata, C. tropicalis and C. albicans. Lectin typing may be of potential value for taxonomic and epidemiological studies of yeasts in clinical laboratories.