Molecular mechanism for pore-formation in lipid membranes by the hemolytic lectin CEL-III from marine invertebrate Cucumaria echinata

Plant lectins: A new antimicrobial frontier

Pathogenic bacteria, viruses, fungi, parasites, and other microbes constantly change to ensure survival. Several pathogens have adopted strict and intricate strategies to fight medical treatments. Many drugs, frequently prescribed to treat these pathogens, are becoming obsolete and ineffective. Because pathogens have gained the capacity to tolerate or resist medications targeted at them, hence the term antimicrobial resistance (AMR), in that regard, many natural compounds have been routinely used as new antimicrobial agents to treat infections. Thus, plant lectins, the carbohydrate-binding proteins, have been targeted as promising drug candidates. This article reviewed more than 150 published papers on plant lectins with promising antibacterial and antifungal properties. We have also demonstrated how some plant lectins could express a synergistic action as adjuvants to boost the efficacy of obsolete or abandoned antimicrobial drugs. Emphasis has also been given to their plausible mechanism of action. The study further reports on the immunomodulatory effect of plant lectins and how they boost the immune system to curb or prevent infection.

Crystallization and preliminary crystallographic study of oligomers of the haemolytic lectin CEL-III from the sea cucumber Cucumaria echinata

CEL-III is a Ca(2+)-dependent haemolytic lectin isolated from the marine invertebrate Cucumaria echinata. This lectin binds to Gal/GalNAc-containing carbohydrate chains on the cell surface and, after conformational changes, oligomerizes to form ion-permeable pores in cell membranes. CEL-III also forms soluble oligomers similar to those formed in cell membranes upon binding of specific carbohydrates in high-pH and high-salt solutions. These soluble and membrane CEL-III oligomers were crystallized and X-ray diffraction data were collected. Crystals of soluble oligomers and membrane oligomers diffracted X-rays to 3.3 and 4.2 Å resolution, respectively, using synchrotron radiation and the former was found to belong to space group C2. Self-rotation functional analysis of the soluble oligomer crystal suggested that it might be composed of heptameric CEL-III.

Holothuria grisea agglutinin (HGA): the first invertebrate lectin with anti-inflammatory effects

Holothuria grisea agglutinin (HGA) is a dimeric lectin of molecular mass 228 kDa by gel filtration with monomers of 105 kDa by SDS-PAGE. The lectin is highly thermostable as it retains full activity for 1 h at 70 °C. Unlike other lectins purified from marine invertebrates, the hemagglutination activity of HGA does not require any divalent metal ions. The affinity analysis of HGA showed that only mucin was able to inhibit the hemagglutinating activity. HGA administered intravenously was tested in classical models of nociception and inflammation. HGA was able to inhibit neutrophil migration into the peritoneal cavity induced by carrageenan. This inhibitory effect was 68% at a dose of 1 mg/kg. In acetic acid-induced writhing tests, a significant antinociceptive effect was observed by treatment with HGA (0.1; 1 or 10 mg/kg) reducing constrictions by 27, 90 and 84%, respectively. In formalin tests, HGA at a dose of 10 mg/kg showed antinociceptive effect only in the inflammatory phase (phase 2). Nevertheless, in hot-plate tests, HGA did not show any nociceptive effect. In rota-rod and open-field tests, HGA did not alter the animals' behavior. The treatment with HGA 10 mg/kg presented diminished myeloperoxidase activity activity (81.6% inhibition) and raised the circulating levels of NO by 50.4% when compared with the carrageenan group. HGA has demonstrated the ability to modulate the inflammatory response in models of inflammation in vivo. HGA is the first marine invertebrate lectin that showed an anti-inflammatory effect. This finding opens a new perspective on the potential of lectins from the marine environment.

Interactions of a lysozyme-monomethoxypolyethylene glycol conjugate with lipopolysaccharides and lipid bilayers and effects of conjugate on gram-negative bacteria

We have been studying a lysozyme derivative, called mPEG-lysozyme, in which Lys 33 is bound with a monomethoxypolyethylene glycol derivative. Here, we examined the surface hydrophobicity of the derivative and also its interactions with lipopolysaccharides and lipid bilayers. These properties may affect the antimicrobial activity of mPEG-lysozyme toward Gram-negative microorganisms. The lysozyme derivative had more than 150% of the antimicrobial activity for such microorganisms with that of native lysozyme taken to be 100%. Spectroscopic analyses indicated that mPEG-lysozyme bound to lipopolysaccharides with higher affinity than lysozyme, because of the high surface hydrophobicity of the derivative. In an experiment on carboxyfluorescein-leakage, mPEG-lysozyme strongly interacted with liposomes constructed from phosphatidylcholine, releasing carboxyfluorescein from the liposomes more effectively than lysozyme did. mPEG-lysozyme may perturb the outer membrane of Gram-negative microorganisms, gaining itself access to the peptidoglycan layers of the bacterium.