The Detection of Bovine Lactoferrin Binding Protein on Toxoplasma gondii

Diverse Mechanisms of Antimicrobial Activities of Lactoferrins, Lactoferricins, and Other Lactoferrin-Derived Peptides

Lactoferrins are an iron-binding glycoprotein that have important protective roles in the mammalian body through their numerous functions, which include antimicrobial, antitumor, anti-inflammatory, immunomodulatory, and antioxidant activities. Among these, their antimicrobial activity has been the most studied, although the mechanism behind antimicrobial activities remains to be elucidated. Thirty years ago, the first lactoferrin-derived peptide was isolated and showed higher antimicrobial activity than the native lactoferrin lactoferricin. Since then, numerous studies have investigated the antimicrobial potencies of lactoferrins, lactoferricins, and other lactoferrin-derived peptides to better understand their antimicrobial activities at the molecular level. This review defines the current antibacterial, antiviral, antifungal, and antiparasitic activities of lactoferrins, lactoferricins, and lactoferrin-derived peptides. The primary focus is on their different mechanisms of activity against bacteria, viruses, fungi, and parasites. The role of their structure, amino-acid composition, conformation, charge, hydrophobicity, and other factors that affect their mechanisms of antimicrobial activity are also reviewed.

Binding and Endocytosis of Bovine Hololactoferrin by the Parasite Entamoeba histolytica

Entamoeba histolytica is a human parasite that requires iron (Fe) for its metabolic function and virulence. Bovine lactoferrin (B-Lf) and its peptides can be found in the digestive tract after dairy products are ingested. The aim of this study was to compare virulent trophozoites recently isolated from hamster liver abscesses with nonvirulent trophozoites maintained for more than 30 years in cultures in vitro regarding their interaction with iron-charged B-Lf (B-holo-Lf). We performed growth kinetics analyses of trophozoites in B-holo-Lf and throughout several consecutive transfers. The virulent parasites showed higher growth and tolerance to iron than nonvirulent parasites. Both amoeba variants specifically bound B-holo-Lf with a similar K_d. However, averages of 9.45 × 10⁵ and 6.65 × 10⁶ binding sites/cell were found for B-holo-Lf in nonvirulent and virulent amoebae, respectively. Virulent amoebae bound more efficiently to human and bovine holo-Lf, human holo-transferrin, and human and bovine hemoglobin than nonvirulent amoebae. Virulent amoebae showed two types of B-holo-Lf binding proteins. Although both amoebae endocytosed this glycoprotein through clathrin-coated vesicles, the virulent amoebae also endocytosed B-holo-Lf through a cholesterol-dependent mechanism. Both amoeba variants secreted cysteine proteases cleaving B-holo-Lf. These data demonstrate that the B-Lf endocytosis is more efficient in virulent amoebae.

Toxoplasma gondii binds sheep prolactin

Taking into account the literature reports on the involvement of prolactin (PRL) in the regulation of immunity against Toxoplasma gondii, we decided to check whether this parasite has the ability to bind the lactotrophic hormone. We examined T. gondii binding of sheep fluoresceine- and biotine-labeled prolactin isolated from pituitary (shPRL). In this work we announced for the first time that shPRL was bound to live tachyzoites of RH (type I) and ME49 (type II) strains. Furthermore, by use of competitive inhibition analysis, we confirmed that this binding was specific for both tested T. gondii strains.

The multifunctional glycolytic protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a novel macrophage lactoferrin receptor1This article is part of Special Issue entitled Lactoferrin and has undergone the Journal's usual peer review process

Several proteins with limited cell type distribution have been shown to bind lactoferrin. However, except in the case of hepatic and intestinal cells, these have not been definitively identified and characterized. Here we report that the multifunctional glycolytic protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH) functions as a novel receptor for lactoferrin (Lf) in macrophages. GAPDH is a well-known moonlighting protein, and previous work from our laboratory has indicated its localization on macrophage cell surfaces, wherein it functions as a transferrin (Tf) receptor. The KD value for GAPDH–lactoferrin interaction was determined to be 43.8 nmol/L. Utilizing co-immunoprecipitation, immunoflorescence, and immunogold labelling electron microscopy we could demonstrate the trafficking of lactoferrin to the endosomal compartment along with GAPDH. We also found that upon iron depletion the binding of lactoferrin to macrophage cell surface is enhanced. This correlated with an increased expression of surface GAPDH, while other known lactoferrin receptors CD14 and lipoprotein receptor-related protein (LRP) were found to remain unaltered in expression levels. This suggests that upon iron depletion, cells prefer to use GAPDH to acquire lactoferrin. As GAPDH is an ubiquitously expressed molecule, its function as a receptor for lactoferrin may not be limited to macrophages.

Iron-saturated lactoferrin and pathogenic protozoa: could this protein be an iron source for their parasitic style of life?

Iron is an essential nutrient for the survival of pathogens inside a host. As a general strategy against microbes, mammals have evolved complex iron-withholding systems for efficiently decreasing the iron accessible to invaders. Pathogens that inhabit the respiratory, intestinal and genitourinary tracts encounter an iron-deficient environment on the mucosal surface, where ferric iron is chelated by lactoferrin, an extracellular glycoprotein of the innate immune system. However, parasitic protozoa have developed several mechanisms to obtain iron from host holo-lactoferrin. Tritrichomonas fetus, Trichomonas vaginalis, Toxoplasma gondii and Entamoeba histolytica express lactoferrin-binding proteins and use holo-lactoferrin as an iron source for growth in vitro; in some species, these binding proteins are immunogenic and, therefore, may serve as potential vaccine targets. Another mechanism to acquire lactoferrin iron has been reported in Leishmania spp. promastigotes, which use a surface reductase to recognize and reduce ferric iron to the accessible ferrous form. Cysteine proteases that cleave lactoferrin have been reported in E. histolytica. This review summarizes the available information on how parasites uptake and use the iron from lactoferrin to survive in hostile host environments.

Identification of Toxoplasma gondii proteins binding human lactoferrin: A new aspect of rhoptry proteins function

In this paper, we report on the isolation, purification and identification of two Toxoplasma gondii membrane proteins binding human lactoferrin. Parasite membrane proteins were isolated using the commercial Mem-PER Eukaryotic Membrane Protein Extraction System. After purification by lactoferrin affinity chromatography, three protein bands were detected with the molecular mass of 74, 63 and 58 kDa, two of which (63 and 58 kDa) specifically bound biotin labeled human lactoferrin as examined by competitive inhibition. Further identification of latter proteins by ESI/MS/MS amino acid sequencing technique revealed those proteins as Toxoplasma ROP4 (band 63 kDa) and ROP2 (band 58 kDa) antigens known to be involved in many mechanisms essential for the parasite pathogenicity, including host lactoferrin acquisition as determined in this study.