Abstract
A specific galactose-binding lectin was shown to inhibit the hemolytic effect of streptolysin O (SLO), an exotoxin produced by Streptococcus pyogenes. Commercially available lectins that recognize N-acetyllactosamine (ECA), T-antigen (PNA), and Tn-antigen (ABA) agglutinated rabbit erythrocytes, but had no effect on SLO-induced hemolysis. In contrast, SLO-induced hemolysis was inhibited by AKL, a lectin purified from sea hare (Aplysia kurodai) eggs that recognizes α-galactoside oligosaccharides. This inhibitory effect was blocked by the co-presence of d-galactose, which binds to AKL. A possible explanation for these findings is that cholesterol-enriched microdomains containing glycosphingolipids in the erythrocyte membrane become occupied by tightly stacked lectin molecules, blocking the interaction between cholesterol and SLO that would otherwise result in penetration of the membrane. Growth of S. pyogenes was inhibited by lectins from a marine invertebrate (AKL) and a mushroom (ABA), but was promoted by a plant lectin (ECA). Both these inhibitory and promoting effects were blocked by co-presence of galactose in the culture medium. Our findings demonstrate the importance of glycans and lectins in regulating mechanisms of toxicity, creation of pores in the target cell membrane, and bacterial growth.
Highlights
Exotoxins are a type of harmful protein secreted by pathogenic microorganisms that damage the host through a specific infectious mechanism
These findings suggest that GSLs targeted by Aplysia kurodai lectin (AKL) are masked by MβCD, such that the lectin cannot bind to glycoconjugates located in cholesterol-enriched microdomains, and that
This concept was supported by SEM observations, which suggested that AKL prevented streptolysin O (SLO) from reaching the RBC membrane and thereby prevented hemolysis (Figure 4A)
Summary
Exotoxins are a type of harmful protein secreted by pathogenic microorganisms that damage the host through a specific infectious mechanism. Streptolysin O (SLO) is an oxygen-labile, thiol-activated hemolytic exotoxin secreted by GAS [3] Pathogenic forms of GAS may cause food poisoning by secreting other virulence factors besides SLO; e.g., streptolysin S (oxygen-stable hemolytic peptide), S. pyogenes exotoxin B (cysteine protease), and NADase (nicotinamide adenine dinucleotide glycohydrolase) [6]. All animals have hemagglutinins or carbohydrate-binding proteins (lectins) that recognize specific glycan structures of glycoconjugates and are able to agglutinate RBCs. Lectins are involved in infectious, toxic, hemolytic, anti-microbial, anti-cancer, and cell signaling processes [7]. We examined the effects of Aplysia kurodai lectin (AKL) on SLO hemolytic activity and on S. pyogenes growth
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