The physico-chemical characteristics of the phosphocholine-containing glycoglycerolipid MfGL-II govern the permeability properties of Mycoplasma fermentans

Infection strategies of mycoplasmas: Unraveling the panoply of virulence factors

Mycoplasmas, the smallest bacteria lacking a cell wall, can cause various diseases in both humans and animals. Mycoplasmas harbor a variety of virulence factors that enable them to overcome numerous barriers of entry into the host; using accessory proteins, mycoplasma adhesins can bind to the receptors or extracellular matrix of the host cell. Although the host immune system can eradicate the invading mycoplasma in most cases, a few sagacious mycoplasmas employ a series of invasion and immune escape strategies to ensure their continued survival within their hosts. For instance, capsular polysaccharides are crucial for anti-phagocytosis and immunomodulation. Invasive enzymes degrade reactive oxygen species, neutrophil extracellular traps, and immunoglobulins. Biofilm formation is important for establishing a persistent infection. During proliferation, successfully surviving mycoplasmas generate numerous metabolites, including hydrogen peroxide, ammonia and hydrogen sulfide; or secrete various exotoxins, such as community-acquired respiratory distress syndrome toxin, and hemolysins; and express various pathogenic enzymes, all of which have potent toxic effects on host cells. Furthermore, some inherent components of mycoplasmas, such as lipids, membrane lipoproteins, and even mycoplasma-generated superantigens, can exert a significant pathogenic impact on the host cells or the immune system. In this review, we describe the proposed virulence factors in the toolkit of notorious mycoplasmas to better understand the pathogenic features of these bacteria, along with their pathogenic mechanisms.

An easy α-glycosylation methodology for the synthesis and stereochemistry of mycoplasma α-glycolipid antigens

Mycoplasma fermentans possesses unique α-glycolipid antigens (GGPL-I and GGPL-III) at the cytoplasm membrane, which carry a phosphocholine group at the sugar primary (6-OH) position. This paper describes a practical synthetic pathway to a GGPL-I homologue (C(16:0)) and its diastereomer, in which our one-pot α-glycosylation method was effectively applied. The synthetic GGPL-I isomers were characterized with (1)H NMR spectroscopy to determine the equilibrium among the three conformers (gg, gt, tg) at the acyclic glycerol moiety. The natural GGPL-I isomer was found to prefer gt (54%) and gg (39%) conformers around the lipid tail, while adopting all of the three conformers with equal probability around the sugar position. This property was very close to what we have observed with respect to the conformation of phosphatidylcholine (DPPC), suggesting that the Mycoplasma glycolipids GGPLs may constitute the cytoplasm fluid membrane together with ubiquitous phospholipids, without inducing stereochemical stress.

Antimicrobial activity of inducible human beta defensin-2 against Mycoplasma pneumoniae

Defensins in innate immunity are known to play critical roles to protect the host from infection by invasive microbes, including Gram-positive and -negative bacteria. However, little is known about the interactions between defensins and mycoplasmas. Human beta defensin (hBD)-2 and hBD-3, but not hBD-1, were found to exert strikingly antimicrobial activity against Mycoplasma pneumoniae. To elucidate the role of defensins in M. pneumoniae infection, a human pulmonary squamous cell line EBC-1 was stimulated with M. pneumoniae and interleukin (IL)-1beta. hBD-2 was markedly upregulated by IL-1beta as well as M. pneumoniae, but neither hBD-1 nor hBD-3 was apparently upregulated. Thus, the results suggest that inducible hBD-2 would play a critical role in the protection of M. pneumoniae infection.

Preparation and Supramolecular Properties of Unadulterated Glycosyl Liposomes from a Bis(α-D-mannopyranosyl)[60]Fullerene Conjugate

The bis(alpha-D-mannopyranosyl)-[60]fullerene conjugate 3 was prepared by thermal coupling of C60 and either 2-azidoethyl 2,3,4,6-tetra-O-acetyl- or 2,3;4,6-di-O-isopropylidene-alpha-D-mannopyranoside (Scheme). Compound 3 was found to readily self-assemble. Dynamic-light-scattering (DLS) and atomic-force microscopy (AFM) experiments supported that the amphiphilic compound gives rise to nano-sized supramolecular structures during sugar deprotection (Ac-group removal) performed in MeOH/CH2Cl2 solution. Encapsulation studies with an aqueous suspension of 3 showed that the self-assembling structure envelopes Ba2+ and the fluorescent dye Acridine Red during its formation, which indicates that it resembles a bilayer vesicle or an unadulterated liposome with an inner hollow space. In addition to this notable property, the unique molecular geometry of the spatially arranged mannosyl surface residues of 3 gives rise to strong binding of the carbohydrate-recognizing lectin Con A. Hence, the polar amphiphilic end of 3 mimics the structure of 3,6-branched tri-alpha-D-mannoside (6; Fig. 3), a natural ligand of the Con A protein.

Physicochemical characterization and biological activity of a glycoglycerolipid from Mycoplasma fermentans

We report a comprehensive physicochemical characterization of a glycoglycerolipid from Mycoplasma fermentans, MfGl-II, in relation to its bioactivity and compared this with the respective behaviors of phosphatidylcholine (PC) and a bacterial glycolipid, lipopolysaccharide (LPS) from deep rough mutant Salmonella minnesota strain R595. The beta left arrow over right arrow alpha gel-to-liquid crystalline phase transition behavior of the hydrocarbon chains with Tc = 30 degrees C for MfGl-II as well as for LPS exhibits high similarity between the two glycolipids. A lipopolysaccharide-binding protein (LBP)-mediated incorporation into negatively charged liposomes is observed for both glycolipids. The determination of the supramolecular aggregate structure confirms the existence of a mixed unilamellar/cubic structure for MfGl-II, similar to that observed for the lipid A moiety of LPS. The biological data clearly show that MfGl-II is able to induce cytokines such as tumor necrosis factor-alpha (TNF-alpha) in human mononuclear cells, although to a significantly lower degree than LPS. In contrast, in the Limulus amebocyte lysate test, MfGl-II is completely inactive, and in the CHO reporter cell line it does not indicate any reactivity with the Toll-like receptors TLR-2 and -4, in contrast to control lipopeptides and LPS. These data confirm the applicability of our conformational concept of endotoxicity to nonlipid A structures: an amphiphilic molecule with a nonlamellar cubic aggregate structure corresponding to a conical conformation of the single molecules and a sufficiently high negative charge density in the backbone.

Interaction of mycoplasmas with host cells

The mycoplasmas form a large group of prokaryotic microorganisms with over 190 species distinguished from ordinary bacteria by their small size, minute genome, and total lack of a cell wall. Owing to their limited biosynthetic capabilities, most mycoplasmas are parasites exhibiting strict host and tissue specificities. The aim of this review is to collate present knowledge on the strategies employed by mycoplasmas while interacting with their host eukaryotic cells. Prominant among these strategies is the adherence of mycoplasma to host cells, identifying the mycoplasmal adhesins as well as the mammalian membrane receptors; the invasion of mycoplasmas into host cells including studies on the role of mycoplasmal surface molecules and signaling mechanisms in the invasion; the fusion of mycoplasmas with host cells, a novel process that raises intriguing questions of how microinjection of mycoplasma components into eukaryotic cells subvert and damage the host cells. The observations of diverse interactions of mycoplasmas with cells of the immune system and their immunomodulatory effects and the discovery of genetic systems that enable mycoplasmas to rapidly change their surface antigenic composition have been important developments in mycoplasma research over the past decade, showing that mycoplasmas possess an impressive capability of maintaining a dynamic surface architecture that is antigenically and functionally versatile, contributing to the capability of the mycoplasmas to adapt to a large range of habitats and cause diseases that are often chronic in nature.

Alternative to fluorescence assays to monitor fusion between Acholeplasma laidlawii cells and liposomes

AIMS

To develop a new technique as an alternative to the fluorescence assays and electron microscopy for the purpose of monitoring the cell-liposome fusion.

METHODS AND RESULTS

Acholeplasma laidlawii whole cells did not oxidize Glucose-6-phosphate (G6P) or Fructose-1,6 diphosphate (F1,6DP) as free (unentrapped) substrates, at concentrations 47 and >270 mM, respectively. Lysed A. laidlawii cells oxidized G6P and F1,6DP at lower concentration of 0.8 and 15 mM, respectively. When these substrates were entrapped inside liposomes, at a final concentration of 1.5 mM, and interacted with A. laidlawii whole cells, in an oxygen electrode chamber, an increase in oxygen uptake was evident. This interaction does not have any effect on cell viability.

SIGNIFICANCE AND IMPACT OF THE STUDY

The experimental system described here is advantageous over classical fluorescence assays in determining the fate of liposome-entrapped material and raises the possibility of studying the kinetics of metabolic substrates, which are normally excluded from the cell by the cell membrane.

Choline-containing lipids in mycoplasmas

Choline-containing lipids were identified and characterized in the cell membrane of Mycoplasma fermentans and were shown to participate in the adhesion to the surface of eukaryotic cells, to stimulate mycoplasma fusion with eukaryotic cells, and to induce cytokine secretion by cells of the immune system. These findings suggest that choline-containing lipids are important mediators of tissue pathology in the infectious process caused by M. fermentans.