Role of binding in Mycoplasma mobile and Mycoplasma pneumoniae gliding analyzed through inhibition by synthesized sialylated compounds

Motility Assays of Mycoplasma mobile Under Light Microscopy

Mycoplasma mobile forms a membrane protrusion at a pole as an organelle. M. mobile cells bind to solid surfaces and glide in the direction of the protrusion. In gliding motility, M. mobile cells catch, pull and release sialylated oligosaccharides on host cells. The observation of Mycoplasma species under light microscopy is useful for the analysis of adhesion ability and the motility mechanism.

Detection of Steps and Rotation in the Gliding Motility of Mycoplasma mobile

Mycoplasma mobile is one of the fastest gliding bacteria, gliding with a speed of 4.5 μm s^-1. This gliding motility is driven by a concerted movement of 450 supramolecular motor units composed of three proteins, Gli123, Gli349, and Gli521, in the gliding motility machinery. With general experimental setups, it is difficult to obtain the information on how each motor unit works. This chapter describes strategies to decrease the number of active motor units to extract stepwise cell movements driven by a minimum number of motor units. We also describe an unforeseen motility mode in which the leg motions convert the gliding motion into rotary motion, which enables us to characterize the motor torque and energy-conversion efficiency by adding some more assumptions.

Reconstitution of a minimal motility system based on Spiroplasma swimming by two bacterial actins in a synthetic minimal bacterium

Motility is one of the most important features of life, but its evolutionary origin remains unknown. In this study, we focused on Spiroplasma, commensal, or parasitic bacteria. They swim by switching the helicity of a ribbon-like cytoskeleton that comprises six proteins, each of which evolved from a nucleosidase and bacterial actin called MreB. We expressed these proteins in a synthetic, nonmotile minimal bacterium, JCVI-syn3B, whose reduced genome was computer-designed and chemically synthesized. The synthetic bacterium exhibited swimming motility with features characteristic of Spiroplasma swimming. Moreover, combinations of Spiroplasma MreB4-MreB5 and MreB1-MreB5 produced a helical cell shape and swimming. These results suggest that the swimming originated from the differentiation and coupling of bacterial actins, and we obtained a minimal system for motility of the synthetic bacterium.

Cell shape controls rheotaxis in small parasitic bacteria

Mycoplasmas, a group of small parasitic bacteria, adhere to and move across host cell surfaces. The role of motility across host cell surfaces in pathogenesis remains unclear. Here, we used optical microscopy to visualize rheotactic behavior in three phylogenetically distant species of Mycoplasma using a microfluidic chamber that enabled the application of precisely controlled fluid flow. We show that directional movements against fluid flow occur synchronously with the polarized cell orienting itself to be parallel against the direction of flow. Analysis of depolarized cells revealed that morphology itself functions as a sensor to recognize rheological properties that mimic those found on host-cell surfaces. These results demonstrate the vital role of cell morphology and motility in responding to mechanical forces encountered in the native environment.

The small, parasitic bacterium Mycoplasma pneumoniae attaches to, and moves over, host cell surfaces. Adherence to host surfaces and motility are critical for the pathogenicity of M. pneumoniae. The role of motility by M. pneumoniae in vivo, however, is poorly understood. Host airways generate constant fluid flow toward the mouth as part of their defense against pathogens and irritants. Consequently, pulmonary invaders must counter the rheological forces found in host airways in order to successfully colonize the host. Here, we demonstrate that M. pneumoniae exhibits directional movement against fluid flow. These findings suggest there is a vital role for rheotactic motility that has evolved in order to overcome host defense mechanisms such as mucociliary clearance.

Force and Stepwise Movements of Gliding Motility in Human Pathogenic Bacterium Mycoplasma pneumoniae

Mycoplasma pneumoniae, a human pathogenic bacterium, binds to sialylated oligosaccharides and glides on host cell surfaces via a unique mechanism. Gliding motility is essential for initiating the infectious process. In the present study, we measured the stall force of an M. pneumoniae cell carrying a bead that was manipulated using optical tweezers on two strains. The stall forces of M129 and FH strains were averaged to be 23.7 and 19.7 pN, respectively, much weaker than those of other bacterial surface motilities. The binding activity and gliding speed of the M129 strain on sialylated oligosaccharides were eight and two times higher than those of the FH strain, respectively, showing that binding activity is not linked to gliding force. Gliding speed decreased when cell binding was reduced by addition of free sialylated oligosaccharides, indicating the existence of a drag force during gliding. We detected stepwise movements, likely caused by a single leg under 0.2-0.3 mM free sialylated oligosaccharides. A step size of 14-19 nm showed that 25-35 propulsion steps per second are required to achieve the usual gliding speed. The step size was reduced to less than half with the load applied using optical tweezers, showing that a 2.5 pN force from a cell is exerted on a leg. The work performed in this step was 16-30% of the free energy of the hydrolysis of ATP molecules, suggesting that this step is linked to the elementary process of M. pneumoniae gliding. We discuss a model to explain the gliding mechanism, based on the information currently available.

Chained Structure of Dimeric F1-like ATPase in Mycoplasma mobile Gliding Machinery

Mycoplasma mobile, a fish pathogen, exhibits gliding motility using ATP hydrolysis on solid surfaces, including animal cells. The gliding machinery can be divided into surface and internal structures. The internal structure of the motor is composed of 28 so-called “chains” that are each composed of 17 repeating protein units called “particles.” These proteins include homologs of the catalytic α and β subunits of F₁-ATPase. In this study, we isolated the particles and determined their structures using negative-staining electron microscopy and high-speed atomic force microscopy. The isolated particles were composed of five proteins, MMOB1660 (α-subunit homolog), -1670 (β-subunit homolog), -1630, -1620, and -4530, and showed ATP hydrolyzing activity. The two-dimensional (2D) structure, with dimensions of 35 and 26 nm, showed a dimer of hexameric ring approximately 12 nm in diameter, resembling F₁-ATPase catalytic (αβ)₃. We isolated the F₁-like ATPase unit, which is composed of MMOB1660, -1670, and -1630. Furthermore, we isolated the chain and analyzed the three-dimensional (3D) structure, showing that dimers of mushroom-like structures resembling F₁-ATPase were connected and aligned along the dimer axis at 31-nm intervals. An atomic model of F₁-ATPase catalytic (αβ)₃ from Bacillus PS3 was successfully fitted to each hexameric ring of the mushroom-like structure. These results suggest that the motor for M. mobile gliding shares an evolutionary origin with F₁-ATPase. Based on the obtained structure, we propose possible force transmission processes in the gliding mechanism.

Molecular ruler of the attachment organelle in Mycoplasma pneumoniae

Length control is a fundamental requirement for molecular architecture. Even small wall-less bacteria have specially developed macro-molecular structures to support their survival. Mycoplasma pneumoniae, a human pathogen, forms a polar extension called an attachment organelle, which mediates cell division, cytadherence, and cell movement at host cell surface. This characteristic ultrastructure has a constant size of 250–300 nm, but its design principle remains unclear. In this study, we constructed several mutants by genetic manipulation to increase or decrease coiled-coil regions of HMW2, a major component protein of 200 kDa aligned in parallel along the cell axis. HMW2-engineered mutants produced both long and short attachment organelles, which we quantified by transmission electron microscopy and fluorescent microscopy with nano-meter precision. This simple design of HMW2 acting as a molecular ruler for the attachment organelle should provide an insight into bacterial cellular organization and its function for their parasitic lifestyles.

Mycoplasma pneumoniae, a pathogen of “walking pneumonia”, have a membrane protrusion with a precise length of 250–300 nm specially developed to support their parasitic lifestyles. To date, however, there has been no report focusing on the potential length-control mechanisms of this characteristic architecture called an attachment organelle. Here, we found that the coiled-coil domains of the 200-kDa protein HMW2 are aligned in parallel along the cell axis, and acts as a molecular ruler by the assembly into a physical scaffold. The molecular ruler could be engineered by genetic modification to produce both longer and shorter attachment organelle. The analyses of the length-controlled mutant highlight a simple design principle of cellular organization in a small bacterium.

Movements of Mycoplasma mobile Gliding Machinery Detected by High-Speed Atomic Force Microscopy

Mycoplasma mobile, a parasitic bacterium, glides on solid surfaces, such as animal cells and glass, by a special mechanism. This process is driven by the force generated through ATP hydrolysis on an internal structure. However, the spatial and temporal behaviors of the internal structures in living cells are unclear. In this study, we detected the movements of the internal structure by scanning cells immobilized on a glass substrate using high-speed atomic force microscopy (HS-AFM). By scanning the surface of a cell, we succeeded in visualizing particles, 2 nm in height and aligned mostly along the cell axis with a pitch of 31.5 nm, consistent with previously reported features based on electron microscopy. Movements of individual particles were then analyzed by HS-AFM. In the presence of sodium azide, the average speed of particle movements was reduced, suggesting that movement is linked to ATP hydrolysis. Partial inhibition of the reaction by sodium azide enabled us to analyze particle behavior in detail, showing that the particles move 9 nm right, relative to the gliding direction, and 2 nm into the cell interior in 330 ms and then return to their original position, based on ATP hydrolysis.

The Sialoglycan Binding Adhesins of Mycoplasma genitalium and Mycoplasma pneumoniae

Mycoplasma genitalium (Mge) and Mycoplasma pneumoniae (Mpn) are two human pathogens associated with urogenital and respiratory tract infections, respectively. The recent elucidation of the tridimensional structure of their major cytoadhesins by X-ray crystallography and cryo-electron microscopy/tomography, has provided important insights regarding the mechanics of infection and evasion of immune surveillance.

Distinct Mycoplasma pneumoniae Interactions with Sulfated and Sialylated Receptors

Mycoplasma pneumoniae is a cell wall-less bacterial pathogen of the conducting airways, causing bronchitis and atypical or "walking" pneumonia in humans. M. pneumoniae recognizes sialylated and sulfated oligosaccharide receptors to colonize the respiratory tract, but the contribution of the latter is particularly unclear. We used chamber slides coated with sulfatide (3-O-sulfogalactosylceramide) to provide a baseline for M. pneumoniae binding and gliding motility. As expected, M. pneumoniae bound to surfaces coated with sulfatide in a manner that was dependent on sulfatide concentration and incubation temperature and inhibited by competing dextran sulfate. However, mycoplasmas bound to sulfatide exhibited no gliding motility, regardless of receptor density. M. pneumoniae also bound lactose 3'-sulfate ligated to an inert polymer scaffold, and binding was inhibited by competing dextran sulfate. The major adhesin protein P1 mediates adherence to terminal sialic acids linked α-2,3, but P1-specific antibodies that blocked M. pneumoniae hemadsorption (HA) and binding to the sialylated glycoprotein laminin by 95% failed to inhibit mycoplasma binding to sulfatide, suggesting that P1 does not mediate binding to sulfated galactose. Consistent with this conclusion, the M. pneumoniae HA-negative mutant II-3 failed to bind to sialylated receptors but adhered to sulfatide in a temperature-dependent manner.

Immunodominant proteins P1 and P40/P90 from human pathogen Mycoplasma pneumoniae

Mycoplasma pneumoniae is a bacterial human pathogen that causes primary atypical pneumonia. M. pneumoniae motility and infectivity are mediated by the immunodominant proteins P1 and P40/P90, which form a transmembrane adhesion complex. Here we report the structure of P1, determined by X-ray crystallography and cryo-electron microscopy, and the X-ray structure of P40/P90. Contrary to what had been suggested, the binding site for sialic acid was found in P40/P90 and not in P1. Genetic and clinical variability concentrates on the N-terminal domain surfaces of P1 and P40/P90. Polyclonal antibodies generated against the mostly conserved C-terminal domain of P1 inhibited adhesion of M. pneumoniae, and serology assays with sera from infected patients were positive when tested against this C-terminal domain. P40/P90 also showed strong reactivity against human infected sera. The architectural elements determined for P1 and P40/P90 open new possibilities in vaccine development against M. pneumoniae infections.

Identification and sequence analyses of the gliding machinery proteins from Mycoplasma mobile

Mycoplasma mobile, a fish pathogen, exhibits its own specialized gliding motility on host cells based on ATP hydrolysis. The special protein machinery enabling this motility is composed of surface and internal protein complexes. Four proteins, MMOBs 1630, 1660, 1670, and 4860 constitute the internal complex, including paralogs of F-type ATPase/synthase α and β subunits. In the present study, the cellular localisation for the candidate gliding machinery proteins, MMOBs 1620, 1640, 1650, and 5430 was investigated by using a total internal reflection fluorescence microscopy system after tagging these proteins with the enhanced yellow fluorescent protein (EYFP). The M. mobile strain expressing a fusion protein MMOB1620-EYFP exhibited reduced cell-binding activity and a strain expressing MMOB1640 fused with EYFP exhibited increased gliding speed, showing the involvement of these proteins in the gliding mechanism. Based on the genomic sequences, we analysed the sequence conservativity in the proteins of the internal and the surface complexes from four gliding mycoplasma species. The proteins in the internal complex were more conserved compared to the surface complex, suggesting that the surface complex undergoes modifications depending on the host. The analyses suggested that the internal gliding complex was highly conserved probably due to its role in the motility mechanism.

Refined Mechanism of Mycoplasma mobile Gliding Based on Structure, ATPase Activity, and Sialic Acid Binding of Machinery

Mycoplasma mobile, a fish pathogen, glides on solid surfaces by repeated catch, pull, and release of sialylated oligosaccharides by a unique mechanism based on ATP energy. The gliding machinery is composed of huge surface proteins and an internal "jellyfish"-like structure. Here, we elucidated the detailed three-dimensional structures of the machinery by electron cryotomography. The internal "tentacle"-like structure hydrolyzed ATP, which was consistent with the fact that the paralogs of the α- and β-subunits of F₁-ATPase are at the tentacle structure. The electron microscopy suggested conformational changes of the tentacle structure depending on the presence of ATP analogs. The gliding machinery was isolated and showed that the binding activity to sialylated oligosaccharide was higher in the presence of ADP than in the presence of ATP. Based on these results, we proposed a model to explain the mechanism of M. mobile gliding.IMPORTANCE The genus Mycoplasma is made up of the smallest parasitic and sometimes commensal bacteria; Mycoplasma pneumoniae, which causes human "walking pneumonia," is representative. More than ten Mycoplasma species glide on host tissues by novel mechanisms, always in the direction of the distal side of the machinery. Mycoplasma mobile, the fastest species in the genus, catches, pulls, and releases sialylated oligosaccharides (SOs), the carbohydrate molecules also targeted by influenza viruses, by means of a specific receptor and using ATP hydrolysis for energy. Here, the architecture of the gliding machinery was visualized three dimensionally by electron cryotomography (ECT), and changes in the structure and binding activity coupled to ATP hydrolysis were discovered. Based on the results, a refined mechanism was proposed for this unique motility.

Identification of novel protein domain for sialyloligosaccharide binding essential to Mycoplasma mobile gliding

Sialic acids, terminal structures of sialylated glycoconjugates, are widely distributed in animal tissues and are often involved in intercellular recognitions, including some bacteria and viruses. Mycoplasma mobile, a fish pathogenic bacterium, binds to sialyloligosaccharide (SO) through adhesin Gli349 and glides on host cell surfaces. The amino acid sequence of Gli349 shows no similarity to known SO-binding proteins. In the present study, we predicted the binding part of Gli349, produced it in Escherichia coli and proved its binding activity to SOs of fetuin using atomic force microscopy. Binding was detected with a frequency of 10.3% under retraction speed of 400 nm/s and was shown to be specific for SO, as binding events were competitively inhibited by the addition of free 3'-sialyllactose. The histogram of the unbinding forces showed 24 pN and additional peaks. These results suggested that the distal end of Gli349 constitutes a novel sialoadhesin domain and is directly involved in the gliding mechanism of M. mobile.

Behaviors and Energy Source of Mycoplasma gallisepticum Gliding

Mycoplasma gallisepticum, an avian-pathogenic bacterium, glides on host tissue surfaces by using a common motility system with Mycoplasma pneumoniae In the present study, we observed and analyzed the gliding behaviors of M. gallisepticum in detail by using optical microscopes. M. gallisepticum glided at a speed of 0.27 ± 0.09 μm/s with directional changes relative to the cell axis of 0.6 degree ± 44.6 degrees/5 s without the rolling of the cell body. To examine the effects of viscosity on gliding, we analyzed the gliding behaviors under viscous environments. The gliding speed was constant in various concentrations of methylcellulose but was affected by Ficoll. To investigate the relationship between binding and gliding, we analyzed the inhibitory effects of sialyllactose on binding and gliding. The binding and gliding speed sigmoidally decreased with sialyllactose concentration, indicating the cooperative binding of the cell. To determine the direct energy source of gliding, we used a membrane-permeabilized ghost model. We permeabilized M. gallisepticum cells with Triton X-100 or Triton X-100 containing ATP and analyzed the gliding of permeabilized cells. The cells permeabilized with Triton X-100 did not show gliding; in contrast, the cells permeabilized with Triton X-100 containing ATP showed gliding at a speed of 0.014 ± 0.007 μm/s. These results indicate that the direct energy source for the gliding motility of M. gallisepticum is ATP.IMPORTANCE Mycoplasmas, the smallest bacteria, are parasitic and occasionally commensal. Mycoplasma gallisepticum is related to human-pathogenic mycoplasmas-Mycoplasma pneumoniae and Mycoplasma genitalium-which cause so-called "walking pneumonia" and nongonococcal urethritis, respectively. These mycoplasmas trap sialylated oligosaccharides, which are common targets among influenza viruses, on host trachea or urinary tract surfaces and glide to enlarge the infected areas. Interestingly, this gliding motility is not related to other bacterial motilities or eukaryotic motilities. Here, we quantitatively analyze cell behaviors in gliding and clarify the direct energy source. The results provide clues for elucidating this unique motility mechanism.

Production and characterization of recombinant P1 adhesin essential for adhesion, gliding, and antigenic variation in the human pathogenic bacterium, Mycoplasma pneumoniae

Mycoplasma pneumoniae forms an attachment organelle at one cell pole, binds to the host cell surface, and glides via a unique mechanism. A 170-kDa protein, P1 adhesin, present on the organelle surface plays a critical role in the binding and gliding process. In this study, we obtained a recombinant P1 adhesin comprising 1476 amino acid residues, excluding the C-terminal domain of 109 amino acids that carried the transmembrane segment, that were fused to additional 17 amino acid residues carrying a hexa-histidine (6 × His) tag using an Escherichia coli expression system. The recombinant protein showed solubility, and chirality in circular dichroism (CD). The results of analytical gel filtration, ultracentrifugation, negative-staining electron microscopy, and small-angle X-ray scattering (SAXS) showed that the recombinant protein exists in a monomeric form with a uniformly folded structure. SAXS analysis suggested the presence of a compact and ellipsoidal structure rather than random or molten globule-like conformation. Structure model based on SAXS results fitted well with the corresponding structure obtained with cryo-electron tomography from a closely related species, M. genitalium. This recombinant protein may be useful for structural and functional studies as well as for the preparation of antibodies for medical applications.

Mycoplasma genitalium adhesin P110 binds sialic-acid human receptors

Adhesion of pathogenic bacteria to target cells is a prerequisite for colonization and further infection. The main adhesins of the emerging sexually transmitted pathogen Mycoplasma genitalium, P140 and P110, interact to form a Nap complex anchored to the cell membrane. Herein, we present the crystal structures of the extracellular region of the virulence factor P110 (916 residues) unliganded and in complex with sialic acid oligosaccharides. P110 interacts only with the neuraminic acid moiety of the oligosaccharides and experiments with human cells demonstrate that these interactions are essential for mycoplasma cytadherence. Additionally, structural information provides a deep insight of the P110 antigenic regions undergoing programmed variation to evade the host immune response. These results enlighten the interplay of M. genitalium with human target cells, offering new strategies to control mycoplasma infections.

How the Mycoplasma genitalium cytadhesins P140 and P110 promote host cell invasion remains poorly understood. Here, combining structural analysis with functional assays, Aparicio et al. identify the P110 domain that binds to sialylated receptors essential for mycoplasma cytadherence.

Sialylated Receptor Setting Influences Mycoplasma pneumoniae Attachment and Gliding Motility

Mycoplasma pneumoniae is a common cause of human respiratory tract infections, including bronchitis and atypical pneumonia. M. pneumoniae binds glycoprotein receptors having terminal sialic acid residues via the P1 adhesin protein. Here, we explored the impact of sialic acid presentation on M. pneumoniae adherence and gliding on surfaces coated with sialylated glycoproteins, or chemically functionalized with α-2,3- and α-2,6-sialyllactose ligated individually or in combination to a polymer scaffold in precisely controlled densities. In both models, gliding required a higher receptor density threshold than adherence, and receptor density influenced gliding frequency but not gliding speed. However, very high densities of α-2,3-sialyllactose actually reduced gliding frequency over peak levels observed at lower densities. Both α-2,3- and α-2,6-sialyllactose supported M. pneumoniae adherence, but gliding was only observed on the former. Finally, gliding on α-2,3-sialyllactose was inhibited on surfaces also conjugated with α-2,6-sialyllactose, suggesting that both moieties bind P1 despite the inability of the latter to support gliding. Our results indicate that the nature and density of host receptor moieties profoundly influences M. pneumoniae gliding, which could affect pathogenesis and infection outcome. Furthermore, precise functionalization of polymer scaffolds shows great promise for further analysis of sialic acid presentation and M. pneumoniae adherence and gliding.

Linear motor driven-rotary motion of a membrane-permeabilized ghost in Mycoplasma mobile

Mycoplasma mobile exhibits a smooth gliding movement as does its membrane-permeabilized ghost model. Ghost experiments revealed that the energy source for M. mobile motility is adenosine triphosphate (ATP) and that the gliding comprises repetitions of 70 nm steps. Here we show a new motility mode, in which the ghost model prepared with 0.013% Triton X-100 exhibits directed rotational motions with an average speed of approximately 2.1 Hz when ATP concentration is greater than 3.0 × 10⁻¹ mM. We found that rotary ghosts treated with sialyllactose, the binding target for leg proteins, were stopped. Although the origin of the rotation has not been conclusively determined, this result suggested that biomolecules embedded on the cell membrane nonspecifically attach to the glass and work as a fluid pivot point and that the linear motion of the leg is a driving force for the rotary motion. This simple geometry exemplifies the new motility mode, by which the movement of a linear motor is efficiently converted to a constant rotation of the object on a micrometer scale.

Detailed Analyses of Stall Force Generation in Mycoplasma mobile Gliding

Mycoplasma mobile is a bacterium that uses a unique mechanism to glide on solid surfaces at a velocity of up to 4.5 μm/s. Its gliding machinery comprises hundreds of units that generate the force for gliding based on the energy derived from ATP; the units catch and pull sialylated oligosaccharides fixed to solid surfaces. In this study, we measured the stall force of wild-type and mutant strains of M. mobile carrying a bead manipulated using optical tweezers. The strains that had been enhanced for binding exhibited weaker stall forces than the wild-type strain, indicating that stall force is related to force generation rather than to binding. The stall force of the wild-type strain decreased linearly from 113 to 19 picoNewtons after the addition of 0-0.5 mM free sialyllactose (a sialylated oligosaccharide), with a decrease in the number of working units. After the addition of 0.5 mM sialyllactose, the cells carrying a bead loaded using optical tweezers exhibited stepwise movements with force increments. The force increments ranged from 1 to 2 picoNewtons. Considering the 70-nm step size, this small-unit force may be explained by the large gear ratio involved in the M. mobile gliding machinery.

Cryo-electron tomography analyses of terminal organelle mutants suggest the motility mechanism of Mycoplasma genitalium

The terminal organelle of Mycoplasma genitalium is responsible for bacterial adhesion, motility and pathogenicity. Localized at the cell tip, it comprises an electron-dense core that is anchored to the cell membrane at its distal end and to the cytoplasm at its proximal end. The surface of the terminal organelle is also covered with adhesion proteins. We performed cellular cryoelectron tomography on deletion mutants of eleven proteins that are implicated in building the terminal organelle, to systematically analyze the ultrastructural effects. These data were correlated with microcinematographies, from which the motility patterns can be quantitatively assessed. We visualized diverse phenotypes, ranging from mild to severe cell adhesion, motility and segregation defects. Based on our observations, we propose a double-spring ratchet model for the motility mechanism that explains our current and previous observations. Our model, which expands and integrates the previously suggested inchworm model, allocates specific functions to each of the essential components of this unique bacterial motility system.

Versatile Methodology for Glycosurfaces: Direct Ligation of Nonderivatized Reducing Saccharides to Poly(pentafluorophenyl acrylate) Grafted Surfaces via Hydrazide Conjugation

In this work, we report a convenient and versatile strategy for surface-grafted glycopolymer constructs with the goal of surface modification that controls the chemical presentation and grafting density of carbohydrate side chains. This approach employs a difunctional hydrazine linker, chemically modified to an active ester containing poly(pentafluorophenyl acrylate) grafted scaffold, to conjugate a variety of saccharides through the reducing end. The successive conjugation steps are carried out under mild conditions and yield high surface densities of sugars, as high as 4.8 nmol·cm^-2, capable of multivalency, with an intact structure and retained bioactivity. We also demonstrate that this glycosylated surface can bind specific lectins according to the structure of its pendant carbohydrate. To demonstrate bioactivity, this surface platform is used to study the binding events of a human respiratory tract pathogen, Mycoplasma pneumoniae, on surfaces conjugated with sialylated sugars.

Structural characterization of the NAP; the major adhesion complex of the human pathogen Mycoplasma genitalium

Mycoplasma genitalium, the causative agent of non-gonococcal urethritis and pelvic inflammatory disease in humans, is a small eubacterium that lacks a peptidoglycan cell wall. On the surface of its plasma membrane is the major surface adhesion complex, known as NAP that is essential for adhesion and gliding motility of the organism. Here, we have performed cryo-electron tomography of intact cells and detergent permeabilized M. genitalium cell aggregates, providing sub-tomogram averages of free and cell-attached NAPs respectively, revealing a tetrameric complex with two-fold rotational (C2) symmetry. Each NAP has two pairs of globular lobes (named α and β lobes), arranged as a dimer of heterodimers with each lobe connected by a stalk to the cell membrane. The β lobes are larger than the α lobes by 20%. Classification of NAPs showed that the complex can tilt with respect to the cell membrane. A protein complex containing exclusively the proteins P140 and P110, was purified from M. genitalium and was structurally characterized by negative-stain single particle EM reconstruction. The close structural similarity found between intact NAPs and the isolated P140/P110 complexes, shows that dimers of P140/P110 heterodimers are the only components of the extracellular region of intact NAPs in M. genitalium.

Chemotaxis without Conventional Two-Component System, Based on Cell Polarity and Aerobic Conditions in Helicity-Switching Swimming of Spiroplasma eriocheiris

Spiroplasma eriocheiris is a pathogen that causes mass mortality in Chinese mitten crab, Eriocheir sinensis. S. eriocheiris causes tremor disease and infects almost all of the artificial breeding crustaceans, resulting in disastrous effects on the aquaculture economy in China. S. eriocheiris is a wall-less helical bacterium, measuring 2.0 to 10.0 μm long, and can swim up to 5 μm per second in a viscous medium without flagella by switching the cell helicity at a kink traveling from the front to the tail. In this study, we showed that S. eriocheiris performs chemotaxis without the conventional two-component system, a system commonly found in bacterial chemotaxis. The chemotaxis of S. eriocheiris was observed more clearly when the cells were cultivated under anaerobic conditions. The cells were polarized as evidenced by a tip structure, swimming in the direction of the tip, and were shown to reverse their swimming direction in response to attractants. Triton X-100 treatment revealed the internal structure, a dumbbell-shaped core in the tip that is connected by a flat ribbon, which traces the shortest line in the helical cell shape from the tip to the other pole. Sixteen proteins were identified as the components of the internal structure by mass spectrometry, including Fibril protein and four types of MreB proteins.

Directed Binding of Gliding Bacterium, Mycoplasma mobile, Shown by Detachment Force and Bond Lifetime

Mycoplasma mobile, a fish-pathogenic bacterium, features a protrusion that enables it to glide smoothly on solid surfaces at a velocity of up to 4.5 µm s⁻¹ in the direction of the protrusion. M. mobile glides by a repeated catch-pull-release of sialylated oligosaccharides fixed on a solid surface by hundreds of 50-nm flexible “legs” sticking out from the protrusion. This gliding mechanism may be explained by a possible directed binding of each leg with sialylated oligosaccharides, by which the leg can be detached more easily forward than backward. In the present study, we used a polystyrene bead held by optical tweezers to detach a starved cell at rest from a glass surface coated with sialylated oligosaccharides and concluded that the detachment force forward is 1.6- to 1.8-fold less than that backward, which may be linked to a catch bond-like behavior of the cell. These results suggest that this directed binding has a critical role in the gliding mechanism.

Mycoplasma species are the smallest bacteria and are parasitic and occasionally commensal, as represented by Mycoplasma pneumoniae, which causes so-called “walking pneumonia” in humans. Dozens of species glide on host tissues, always in the direction of the characteristic cellular protrusion, by novel mechanisms. The fastest species, Mycoplasma mobile, catches, pulls, and releases sialylated oligosaccharides (SOs), which are common targets among influenza viruses, by means of a specific receptor based on the energy of ATP hydrolysis. Here, force measurements made with optical tweezers revealed that the force required to detach a cell from SOs is smaller forward than backward along the gliding direction. The directed binding should be a clue to elucidate this novel motility mechanism.

Integrated Information and Prospects for Gliding Mechanism of the Pathogenic Bacterium Mycoplasma pneumoniae

Mycoplasma pneumoniae forms a membrane protrusion at a cell pole and is known to adhere to solid surfaces, including animal cells, and can glide on these surfaces with a speed up to 1 μm per second. Notably, gliding appears to be involved in the infectious process in addition to providing the bacteria with a means of escaping the host's immune systems. However, the genome of M. pneumoniae does not encode any of the known genes found in other bacterial motility systems or any conventional motor proteins that are responsible for eukaryotic motility. Thus, further analysis of the mechanism underlying M. pneumoniae gliding is warranted. The gliding machinery formed as the membrane protrusion can be divided into the surface and internal structures. On the surface, P1 adhesin, a 170 kDa transmembrane protein forms an adhesin complex with other two proteins. The internal structure features a terminal button, paired plates, and a bowl (wheel) complex. In total, the organelle is composed of more than 15 proteins. By integrating the currently available information by genetics, microscopy, and structural analyses, we have suggested a working model for the architecture of the organelle. Furthermore, in this article, we suggest and discuss a possible mechanism of gliding based on the structural model, in which the force generated around the bowl complex transmits through the paired plates, reaching the adhesin complex, resulting in the repeated catch of sialylated oligosaccharides on the host surface by the adhesin complex.

Novel mechanisms power bacterial gliding motility

For many bacteria, motility is essential for survival, growth, virulence, biofilm formation and intra/interspecies interactions. Since natural environments differ, bacteria have evolved remarkable motility systems to adapt, including swimming in aqueous media, and swarming, twitching and gliding on solid and semi-solid surfaces. Although tremendous advances have been achieved in understanding swimming and swarming motilities powered by flagella, and twitching motility powered by Type IV pili, little is known about gliding motility. Bacterial gliders are a heterogeneous group containing diverse bacteria that utilize surface motilities that do not depend on traditional flagella or pili, but are powered by mechanisms that are less well understood. Recently, advances in our understanding of the molecular machineries for several gliding bacteria revealed the roles of modified ion channels, secretion systems and unique machinery for surface movements. These novel mechanisms provide rich source materials for studying the function and evolution of complex microbial nanomachines. In this review, we summarize recent findings made on the gliding mechanisms of the myxobacteria, flavobacteria and mycoplasmas.

Periodicity in Attachment Organelle Revealed by Electron Cryotomography Suggests Conformational Changes in Gliding Mechanism of Mycoplasma pneumoniae

Mycoplasma pneumoniae, a pathogenic bacterium, glides on host surfaces using a unique mechanism. It forms an attachment organelle at a cell pole as a protrusion comprised of knoblike surface structures and an internal core. Here, we analyzed the three-dimensional structure of the organelle in detail by electron cryotomography. On the surface, knoblike particles formed a two-dimensional array, albeit with limited regularity. Analyses using a nonbinding mutant and an antibody showed that the knoblike particles correspond to a naplike structure that has been observed by negative-staining electron microscopy and is likely to be formed as a complex of P1 adhesin, the key protein for binding and gliding. The paired thin and thick plates feature a rigid hexagonal lattice and striations with highly variable repeat distances, respectively. The combination of variable and invariant structures in the internal core and the P1 adhesin array on the surface suggest a model in which axial extension and compression of the thick plate along a rigid thin plate is coupled with attachment to and detachment from the substrate during gliding.

Human mycoplasma pneumonia, epidemic all over the world in recent years, is caused by a pathogenic bacterium, Mycoplasma pneumoniae. This tiny bacterium, about 2 µm in cell body length, glides on the surface of the human trachea to infect the host by binding to sialylated oligosaccharides, which are also the binding targets of influenza viruses. The mechanism of mycoplasmal gliding motility is not related to any other well-studied motility systems, such as bacterial flagella and cytoplasmic motor proteins. Here, we visualized the attachment organelle, a cellular architecture for gliding, three dimensionally by using electron cryotomography and other conventional methods. A possible gliding mechanism has been suggested based on the architectural images.

Potential Molecular Targets for Narrow-Spectrum Agents to Combat Mycoplasma pneumoniae Infection and Disease

As Mycoplasma pneumoniae macrolide resistance grows and spreads worldwide, it is becoming more important to develop new drugs to prevent infection or limit disease. Because other mycoplasma species have acquired resistance to other classes of antibiotics, it is reasonable to presume that M. pneumoniae can do the same, so switching to commonly used antibiotics like fluoroquinolones will not result in forms of therapy with long-term utility. Moreover, broad-spectrum antibiotics can have serious consequences for the patient, as these drugs may have severe impacts on the natural microbiota of the individual, compromising the health of the patient either short-term or long-term. Therefore, developing narrow-spectrum antibiotics that effectively target only M. pneumoniae and no more than a small portion of the microbiota is likely to yield impactful, positive results that can be used perhaps indefinitely to combat M. pneumoniae. Development of these agents requires a deep understanding of the basic biology of M. pneumoniae, in many areas deeper than what is currently known. In this review, we discuss potential targets for new, narrow-spectrum agents and both the positive and negative aspects of selecting these targets, which include toxic molecules, metabolic pathways, and attachment and motility. By gathering this information together, we anticipate that it will be easier for researchers to evaluate topics of priority for study of M. pneumoniae.

Reprint of “Prospects for the gliding mechanism of Mycoplasma mobile”

Mycoplasma mobile forms gliding machinery at a cell pole and glides continuously in the direction of the cell pole at up to 4.5 μm per second on solid surfaces such as animal cells. This motility system is not related to those of any other bacteria or eukaryotes. M. mobile uses ATP energy to repeatedly catch, pull, and release sialylated oligosaccharides on host cells with its approximately 50-nm long legs. The gliding machinery is a large structure composed of huge surface proteins and internal jellyfish-like structure. This system may have developed from an accidental combination between an adhesin and a rotary ATPase, both of which are essential for the adhesive parasitic life of Mycoplasmas.

Systematic Structural Analyses of Attachment Organelle in Mycoplasma pneumoniae

Mycoplasma pneumoniae, a human pathogenic bacterium, glides on host cell surfaces by a unique and unknown mechanism. It forms an attachment organelle at a cell pole as a membrane protrusion composed of surface and internal structures, with a highly organized architecture. In the present study, we succeeded in isolating the internal structure of the organelle by sucrose-gradient centrifugation. The negative-staining electron microscopy clarified the details and dimensions of the internal structure, which is composed of terminal button, paired plates, and bowl complex from the end of cell front. Peptide mass fingerprinting of the structure suggested 25 novel components for the organelle, and 3 of them were suggested for their involvement in the structure through their subcellular localization determined by enhanced yellow fluorescent protein (EYFP) tagging. Thirteen component proteins including the previously reported ones were mapped on the organelle systematically for the first time, in nanometer order by EYFP tagging and immunoelectron microscopy. Two, three, and six specific proteins localized specifically to the terminal button, the paired plates, and the bowl, respectively and interestingly, HMW2 molecules were aligned parallel to form the plate. The integration of these results gave the whole image of the organelle and allowed us to discuss possible gliding mechanisms.

Human mycoplasma pneumonia, an epidemic of which occurred around the world a few years ago, is caused by a pathogenic bacterium, Mycoplasma pneumoniae. This tiny bacterium, about 2 μm long, infects humans by gliding on the surface of the trachea through binding to sialylated oligosaccharides, which are also the binding targets of influenza viruses. The mechanism underlying Mycoplasma "gliding motility" is not related to any other well-studied motility systems, such as bacterial flagella and eukaryotic motor proteins. Here, we isolated the internal structure of “attachment organelle", a cellular architecture, and suggested novel component proteins. The organelle was analyzed systematically by focusing on the protein components under fluorescence and electron microscopy, and a possible gliding mechanism was suggested.

Three-Dimensional Superlocalization Imaging of Gliding Mycoplasma mobile by Extraordinary Light Transmission through Arrayed Nanoholes

In this paper, we describe super-resolved sampling of live bacteria based on extraordinary optical transmission (EOT) of light. EOT is produced by surface plasmon confinement and coupling with nanostructures. Bacterial fluorescence is excited by the localized fields for subdiffraction-limited sampling. The concept was applied to elucidating bacterial dynamics of gliding Mycoplasma mobile (M. mobile). The results analyzed with multiple M. mobile bacteria show individual characters and reveal that M. mobile undergoes a significant axial variation at 94 nm. The sampling error of the method is estimated to be much smaller than 1/10 of the diffraction limit both in the lateral and depth axis. The method provides a powerful tool for investigation of biomolecular dynamics at subwavelength precision.

Gliding Direction of Mycoplasma mobile

Mycoplasma mobile glides in the direction of its cell pole by a unique mechanism in which hundreds of legs, each protruding from its own gliding unit, catch, pull, and release sialylated oligosaccharides fixed on a solid surface. In this study, we found that 77% of cells glided to the left with a change in direction of 8.4° ± 17.6° μm(-1) displacement. The cell body did not roll around the cell axis, and elongated, thinner cells also glided while tracing a curved trajectory to the left. Under viscous conditions, the range of deviation of the gliding direction decreased. In the presence of 250 μM free sialyllactose, in which the binding of the legs (i.e., the catching of sialylated oligosaccharides) was reduced, 70% and 30% of cells glided to the left and the right, respectively, with changes in direction of ∼30° μm(-1). The gliding ghosts, in which a cell was permeabilized by Triton X-100 and reactivated by ATP, glided more straightly. These results can be explained by the following assumptions based on the suggested gliding machinery and mechanism: (i) the units of gliding machinery may be aligned helically around the cell, (ii) the legs extend via the process of thermal fluctuation and catch the sialylated oligosaccharides, and (iii) the legs generate a propulsion force that is tilted from the cell axis to the left in 70% and to the right in 30% of cells.

IMPORTANCE

Mycoplasmas are bacteria that are generally parasitic to animals and plants. Some Mycoplasma species form a protrusion at a pole, bind to solid surfaces, and glide. Although these species appear to consistently glide in the direction of the protrusion, their exact gliding direction has not been examined. This study analyzed the gliding direction in detail under various conditions and, based on the results, suggested features of the machinery and the mechanism of gliding.

Prospects for the gliding mechanism of Mycoplasma mobile

Mycoplasma mobile forms gliding machinery at a cell pole and glides continuously in the direction of the cell pole at up to 4.5μm per second on solid surfaces such as animal cells. This motility system is not related to those of any other bacteria or eukaryotes. M. mobile uses ATP energy to repeatedly catch, pull, and release sialylated oligosaccharides on host cells with its approximately 50-nm long legs. The gliding machinery is a large structure composed of huge surface proteins and internal jellyfish-like structure. This system may have developed from an accidental combination between an adhesin and a rotary ATPase, both of which are essential for the adhesive parasitic life of Mycoplasmas.

Gliding Motility of Mycoplasma mobile on Uniform Oligosaccharides

The binding and gliding of Mycoplasma mobile on a plastic plate covered by 53 uniform oligosaccharides were analyzed. Mycoplasmas bound to and glided on only 21 of the fixed sialylated oligosaccharides (SOs), showing that sialic acid is essential as the binding target. The affinities were mostly consistent with our previous results on the inhibitory effects of free SOs and suggested that M. mobile recognizes SOs from the nonreducing end with four continuous sites as follows. (i and ii) A sialic acid at the nonreducing end is tightly recognized by tandemly connected two sites. (iii) The third site is recognized by a loose groove that may be affected by branches. (iv) The fourth site is recognized by a large groove that may be enhanced by branches, especially those with a negative charge. The cells glided on uniform SOs in manners apparently similar to those of the gliding on mixed SOs. The gliding speed was related inversely to the mycoplasma's affinity for SO, suggesting that the detaching step may be one of the speed determinants. The cells glided faster and with smaller fluctuations on the uniform SOs than on the mixtures, suggesting that the drag caused by the variation in SOs influences gliding behaviors.

IMPORTANCE

Mycoplasma is a group of bacteria generally parasitic to animals and plants. Some Mycoplasma species form a protrusion at a pole, bind to solid surfaces, and glide in the direction of the protrusion. These procedures are essential for parasitism. Usually, mycoplasmas glide on mixed sialylated oligosaccharides (SOs) derived from glycoprotein and glycolipid. Since gliding motility on uniform oligosaccharides has never been observed, this study gives critical information about recognition and interaction between receptors and SOs.

First identification of proteins involved in motility of Mycoplasma gallisepticum

Mycoplasma gallisepticum, the most pathogenic mycoplasma in poultry, is able to glide over solid surfaces. Although this gliding motility was first observed in 1968, no specific protein has yet been shown to be involved in gliding. We examined M. gallisepticum strains and clonal variants for motility and found that the cytadherence proteins GapA and CrmA were required for gliding. Loss of GapA or CrmA resulted in the loss of motility and hemadsorption and led to drastic changes in the characteristic flask-shape of the cells. To identify further genes involved in motility, a transposon mutant library of M. gallisepticum was generated and screened for motility-deficient mutants, using a screening assay based on colony morphology. Motility-deficient mutants had transposon insertions in gapA and the neighbouring downstream gene crmA. In addition, insertions were seen in gene mgc2, immediately upstream of gapA, in two motility-deficient mutants. In contrast to the GapA/CrmA mutants, the mgc2 motility mutants still possessed the ability to hemadsorb. Complementation of these mutants with a mgc2-hexahistidine fusion gene restored the motile phenotype. This is the first report assigning specific M. gallisepticum proteins to involvement in gliding motility.

Unitary step of gliding machinery in Mycoplasma mobile

Among the bacteria that glide on substrate surfaces, Mycoplasma mobile is one of the fastest, exhibiting smooth movement with a speed of 2.0-4.5 μm⋅s(-1) with a cycle of attachment to and detachment from sialylated oligosaccharides. To study the gliding mechanism at the molecular level, we applied an assay with a fluorescently labeled and membrane-permeabilized ghost model, and investigated the motility by high precision colocalization microscopy. Under conditions designed to reduce the number of motor interactions on a randomly oriented substrate, ghosts took unitary 70-nm steps in the direction of gliding. Although it remains possible that the stepping behavior is produced by multiple interactions, our data suggest that these steps are produced by a unitary gliding machine that need not move between sites arranged on a cytoskeletal lattice.

Cytadherence of Mycoplasma pneumoniae induces inflammatory responses through autophagy and toll-like receptor 4

Mycoplasma pneumoniae causes pneumonia, tracheobronchitis, pharyngitis, and asthma in humans. The pathogenesis of M. pneumoniae infection is attributed to excessive immune responses. We previously demonstrated that M. pneumoniae lipoproteins induced inflammatory responses through Toll-like receptor 2 (TLR2). In the present study, we demonstrated that M. pneumoniae induced strong inflammatory responses in macrophages derived from TLR2 knockout (KO) mice. Cytokine production in TLR2 KO macrophages was increased compared with that in the macrophages of wild-type (WT) mice. Heat-killed, antibiotic-treated, and overgrown M. pneumoniae failed to induce inflammatory responses in TLR2 KO macrophages. 3-Methyladenine and chloroquine, inhibitors of autophagy, decreased the induction of inflammatory responses in TLR2 KO macrophages. These inflammatory responses were also inhibited in macrophages treated with the TLR4 inhibitor VIPER and those obtained from TLR2 and TLR4 (TLR2/4) double-KO mice. Two mutants that lacked the ability to induce inflammatory responses in TLR2 KO macrophages were obtained by transposon mutagenesis. The transposons were inserted in atpC encoding an ATP synthase F0F1 ε subunit and F10_orf750 encoding hypothetical protein MPN333. These mutants showed deficiencies in cytadherence. These results suggest that cytadherence of M. pneumoniae induces inflammatory responses through TLR4 and autophagy.

Localization of P42 and F(1)-ATPase α-subunit homolog of the gliding machinery in Mycoplasma mobile revealed by newly developed gene manipulation and fluorescent protein tagging

Mycoplasma mobile has a unique mechanism that enables it to glide on solid surfaces faster than any other gliding mycoplasma. To elucidate the gliding mechanism, we developed a transformation system for M. mobile based on a transposon derived from Tn4001. Modification of the electroporation conditions, outgrowth time, and colony formation from the standard method for Mycoplasma species enabled successful transformation. A fluorescent-protein tagging technique was developed using the enhanced yellow fluorescent protein (EYFP) and applied to two proteins that have been suggested to be involved in the gliding mechanism: P42 (MMOB1050), which is transcribed as continuous mRNA with other proteins essential for gliding, and a homolog of the F1-ATPase α-subunit (MMOB1660). Analysis of the amino acid sequence of P42 by PSI-BLAST suggested that P42 evolved from a common ancestor with FtsZ, the bacterial tubulin homologue. The roles of P42 and the F(1)-ATPase subunit homolog are discussed as part of our proposed gliding mechanism.

Quantitative assessment of Mycoplasma hemadsorption activity by flow cytometry

A number of adherent mycoplasmas have developed highly complex polar structures that are involved in diverse aspects of the biology of these microorganisms and play a key role as virulence factors by promoting adhesion to host cells in the first stages of infection. Attachment activity of mycoplasma cells has been traditionally investigated by determining their hemadsorption ability to red blood cells and it is a distinctive trait widely examined when characterizing the different mycoplasma species. Despite the fact that protocols to qualitatively determine the hemadsorption or hemagglutination of mycoplasmas are straightforward, current methods when investigating hemadsorption at the quantitative level are expensive and poorly reproducible. By using flow cytometry, we have developed a procedure to quantify rapidly and accurately the hemadsorption activity of mycoplasmas in the presence of SYBR Green I, a vital fluorochrome that stains nucleic acids, allowing to resolve erythrocyte and mycoplasma cells by their different size and fluorescence. This method is very reproducible and permits the kinetic analysis of the obtained data and a precise hemadsorption quantification based on standard binding parameters such as the dissociation constant K_d. The procedure we developed could be easily implemented in a standardized assay to test the hemadsorption activity of the growing number of clinical isolates and mutant strains of different mycoplasma species, providing valuable data about the virulence of these microorganisms.

In vitro spatial and temporal analysis of Mycoplasma pneumoniae colonization of human airway epithelium

Mycoplasma pneumoniae is an important cause of respiratory disease, especially in school-age children and young adults. We employed normal human bronchial epithelial (NHBE) cells in air-liquid interface culture to study the interaction of M. pneumoniae with differentiated airway epithelium. These airway cells, when grown in air-liquid interface culture, polarize, form tight junctions, produce mucus, and develop ciliary function. We examined both qualitatively and quantitatively the role of mycoplasma gliding motility in the colonization pattern of developing airway cells, comparing wild-type M. pneumoniae and mutants thereof with moderate to severe defects in gliding motility. Adherence assays with radiolabeled mycoplasmas demonstrated a dramatic reduction in binding for all strains with airway cell polarization, independent of acquisition of mucociliary function. Adherence levels dropped further once NHBE cells achieved terminal differentiation, with mucociliary activity strongly selecting for full gliding competence. Analysis over time by confocal microscopy demonstrated a distinct colonization pattern that appeared to originate primarily with ciliated cells, but lateral spread from the base of the cilia was slower than expected. The data support a model in which the mucociliary apparatus impairs colonization yet cilia provide a conduit for mycoplasma access to the host cell surface and suggest acquisition of a barrier function, perhaps associated with tethered mucin levels, with NHBE cell polarization.