Zipper Mechanism Research Articles

2-dimensional impact-damping electrostatic actuators with elastomer-enhanced auxetic structure

Biomimetic robots yearn for compliant actuators that are comparable to biological muscle in both functions and structural properties. For that, electrostatic actuators have been developed to imitate bio-muscle in features of fast response, high power, energy-efficiency, etc. However, those actuators typically lack impact damping performance, making them vulnerable and unstable in real applications. Here, we present auxetic electrostatic actuators that address this issue and demonstrate muscle-like performance by using elastomer-enhanced auxetics and electrostatic zipping mechanism. The proposed actuators contract linearly on applied voltage, producing large actuation strength (15 N) and contraction ratio (59%). Fabricated from readily available materials, our prototypes can quickly attenuate vibrations caused by impacts and absorb shock energy in 0.3 s. Furthermore, leveraging their 2-dimensional working mode and self-locking mechanism, a stiffness-changing muscle for a robotic arm and an active tensegrity device exemplify the potential applications of auxetic electrostatic actuators to a wide range of bionic robots.

Morphology evolution of supramolecular aggregates from C3-symmetric peptide amphiphiles

During the aging of supramolecular systems, new stable materials with different morphologies, molecular packing, and hierarchical organization may form from the initial assembly. Understanding the mechanisms and pathways accompanying age-related changes may allow for the controlled synthesis of multiple materials from a single molecule in a nature-inspired manner. Herein, we demonstrate the multi-stage evolution of a single solution of C3-symmetric peptide amphiphile containing diphenylalanine fragment and benzyl-1,3,5-tricarboxamide core. Transmission electron microscopy reveals the rapid formation of 20–40 nm wide nanoribbons in an aqueous solution within 60 s after preparation. The lateral edges of nanoribbons contain solvent-exposed aromatic residues that tend to merge via an unconventional edge-to-edge zipping mechanism, leading to the nanoribbon’s growth in width. After reaching a critical width and flexibility, “sticky edges” on the same nanoribbon may merge via a self-zipping mechanism, forming rigid nanotubes. Eventually, mechanical perturbations cause buckling and fracture of nanotubes into shorter nanotubes via flexural or tensile failure. This work reports new evolution pathways in soft 2D assemblies and introduces solution ageing as a promising method to control morphology of peptide amphiphiles.

Mfn2-dependent fusion pathway of PE-enriched micron-sized vesicles

Mitofusins (Mfn1 and Mfn2) are the mitochondrial outer-membrane fusion proteins in mammals and belong to the dynamin superfamily of multidomain GTPases. Recent structural studies of truncated variants lacking alpha helical transmembrane domains suggested that Mfns dimerize to promote the approximation and the fusion of the mitochondrial outer membranes upon the hydrolysis of guanine 5'-triphosphate disodium salt (GTP). However, next to the presence of GTP, the fusion activity seems to require multiple regulatory factors that control the dynamics and kinetics of mitochondrial fusion through the formation of Mfn1-Mfn2 heterodimers. Here, we purified and reconstituted the full-length murine Mfn2 protein into giant unilamellar vesicles (GUVs) with different lipid compositions. The incubation with GTP resulted in the fusion of Mfn2-GUVs. High-speed video-microscopy showed that the Mfn2-dependent membrane fusion pathway progressed through a zipper mechanism where the formation and growth of an adhesion patch eventually led to the formation of a membrane opening at the rim of the septum. The presence of physiological concentration (up to 30 mol%) of dioleoyl-phosphatidylethanolamine (DOPE) was shown to be a requisite to observe GTP-induced Mfn2-dependent fusion. Our observations show that Mfn2 alone can promote the fusion of micron-sized DOPE-enriched vesicles without the requirement of regulatory cofactors, such as membrane curvature, or the assistance of other proteins.

Improvising on the Fly: Comparison of a Novel Technique for Emergent Zipper Release to a Well-Established Technique in a Simulated Setting

BackgroundPenile skin zipper entrapment is an emergent medical condition in which the penile skin, scrotal skin, or foreskin gets caught within the teeth of a zipper or the slider itself. This can lead to complications such as urethral involvement, skin loss, or tissue necrosis. We propose a novel technique to aid in the release of entrapped skin utilizing wire cutters directed at the inferior portion of the zipper pull. ObjectivesTo describe a novel technique to free entrapped penile skin and compare its performance to the well-established median bar technique in a simulated setting. MethodsA randomized cross-over design was used to compare techniques on successful release, time to release and tissue injury using an animal model of raw chicken skin entrapped in a zipper. Statistical significance was assessed at p < 0.05. ResultsTwenty-two participants were included. There was no statistically significant difference between the novel technique and the median bar technique regarding successful release (100% vs 95.5%, respectively), median time to release (29.1 vs 26.4 seconds, respectively), or frequency of tissue injury (22.7% vs 27.3%). ConclusionPerformance using our novel technique for removal of penile skin from a zipper is similar to the median bar release technique regarding. Our novel technique may be a valid treatment option for the release of entrapped penile skin in a zipper mechanism in the emergency department setting.

A Single-Crystal Monomer to Single-Crystal Polymer Reaction Activated by a Triplet Excimer in a Zipper Mechanism.

A combined experimental and theoretical study focused on the elucidation of the polymerization mechanism of the crystal monomer to crystal polymer reaction of a bisindenedione compound in the solid state. The experimental description and characterization of the polymer product have been reported elsewhere and, in this article, we address the first detailed description of the polymerization process. This reaction pathway consists of the initial formation of a triplet excimer state that relaxes to an intermolecularly bonded triplet state that is the starting point of the propagation step of the polymerization. The overall process can be visualized in the monomer starting state as an open zipper in which a cursor or slider is formed by light absorption and the whole zipper is then closed by propagation of the cursor. To this end, variable-temperature electron spin resonance (ESR), femtosecond transient absorption spectroscopy, and vibrational Raman spectroscopic data have been implemented in combination with quantum chemical calculations. The presented mechanistic insight is of great value to understand the intricacies of such an important reaction and to envisage and diversify the products produced thereof.

A Single‐Crystal Monomer to Single‐Crystal Polymer Reaction Activated by a Triplet Excimer in a Zipper Mechanism

AbstractA combined experimental and theoretical study focused on the elucidation of the polymerization mechanism of the crystal monomer to crystal polymer reaction of a bisindenedione compound in the solid state. The experimental description and characterization of the polymer product have been reported elsewhere and, in this article, we address the first detailed description of the polymerization process. This reaction pathway consists of the initial formation of a triplet excimer state that relaxes to an intermolecularly bonded triplet state that is the starting point of the propagation step of the polymerization. The overall process can be visualized in the monomer starting state as an open zipper in which a cursor or slider is formed by light absorption and the whole zipper is then closed by propagation of the cursor. To this end, variable‐temperature electron spin resonance (ESR), femtosecond transient absorption spectroscopy, and vibrational Raman spectroscopic data have been implemented in combination with quantum chemical calculations. The presented mechanistic insight is of great value to understand the intricacies of such an important reaction and to envisage and diversify the products produced thereof.

The bacterial lectin LecA from P. aeruginosa alters membrane organization by dispersing ordered domains

The dynamic reorganization of plasma membrane nanodomains (lipid rafts) plays a key role in host cell infection by human pathogens. Bacteria can induce the reorganization of lipid rafts as a result of the interactions between bacterial lectins and lipid raft glycosphingolipids (GSLs). However, it is still unclear how such interactions trigger the initial stage of the infection mechanism. Here, we study the GSL globotriaosylceramide (Gb3), a key receptor involved in the cellular uptake of the Gram-negative bacterium P. aeruginosa. The bacterial surface lectin LecA targets Gb3 and promotes bacterial invasion via a lipid zipper mechanism. We mimic the plasma membrane using supported lipid bilayers (SLBs), containing liquid-ordered and liquid-disordered lipid domains. We observe that the liquid-ordered domains in the SLBs disperse upon interaction with LecA, accompanied by a deformation of SLBs surface. Our results link the membrane reorganization triggered by LecA with the P. aeruginosa infections in host cells.

Epithelial cell invasion by salmonella typhimurium induces modulation of genes controlled by aryl hydrocarbon receptor signaling and involved in extracellular matrix biogenesis

ABSTRACT Salmonella is the only bacterium able to enter a host cell by the two known mechanisms: trigger and zipper. The trigger mechanism relies on the injection of bacterial effectors into the host cell through the Salmonella type III secretion system 1. In the zipper mechanism, mediated by the invasins Rck and PagN, the bacterium takes advantage of a cellular receptor for invasion. This study describes the transcriptomic reprogramming of the IEC-6 intestinal epithelial cell line to Salmonella Typhimurium strains that invaded cells by a trigger, a zipper, or both mechanisms. Using S. Typhimurium strains invalidated for one or other entry mechanism, we have shown that IEC-6 cells could support both entries. Comparison of the gene expression profiles of exposed cells showed that irrespective of the mechanism used for entry, the transcriptomic reprogramming of the cell was nearly the same. On the other hand, when gene expression was compared between cells unexposed or exposed to the bacterium, the transcriptomic reprogramming of exposed cells was significantly different. It is particularly interesting to note the modulation of expression of numerous target genes of the aryl hydrocarbon receptor showing that this transcription factor was activated by S. Typhimurium infection. Numerous genes associated with the extracellular matrix were also modified. This was confirmed at the protein level by western-blotting showing a dramatic modification in some extracellular matrix proteins. Analysis of a selected set of modulated genes showed that the expression of the majority of these genes was modulated during the intracellular life of S. Typhimurium.

High-Performance Ionanofluids from Subzipped Carbon Nanotube Networks

Investments in the transfer and storage of thermal energy along with renewable energy sources strengthen health and economic infrastructure. These factors intensify energy diversification and the more rapid post-COVID recovery of economies. Ionanofluids (INFs) composed of long multiwalled carbon nanotubes (MWCNTs) rich in sp2-hybridized atoms and ionic liquids (ILs) display excellent thermal conductivity enhancement with respect to the pure IL, high thermal stability, and attractive rheology. However, the influence of the morphology, physicochemistry of nanoparticles and the IL-nanostructure interactions on the mechanism of heat transfer and rheological properties of INFs remain unidentified. Here, we show that intertube nanolayer coalescence, supported by 1D geometry assembly, leads to the subzipping of MWCNT bundles and formation of thermal bridges toward 3D networks in the whole INF volume. We identified stable networks of straight and bent MWCNTs separated by a layer of ions at the junctions. We found that the interactions between the ultrasonication-induced breaking nanotubes and the cations were covalent in nature. Furthermore, we found that the ionic layer imposed by close MWCNT surfaces favored enrichment of the cis conformer of the bis(trifluoromethylsulfonyl)imide anion. Our results demonstrate how the molecular perfection of the MWCNT structure with its supramolecular arrangement affects the extraordinary thermal conductivity enhancement of INFs. Thus, we gave the realistic description of the interactions at the IL-CNT interface with its (super)structure and chemistry as well as the molecular structure of the continuous phase. We anticipate our results to be a starting point for more complex studies on the supramolecular zipping mechanism. For example, ionically functionalized MWCNTs toward polyionic systems─of projected and controlled nanolayers─could enable the design of even more efficient heat-transfer fluids and miniaturization of flexible electronics.

Recognition of Aβ oligomer by LilrB2 acceptor: a tetracoordinated zipper mechanism.

Leukocyte immunoglobulin-like receptor B2 (LilrB2) is one of discovered cell surface β-amyloid (Aβ) receptors and taken as a promising therapeutic target for the treatment of Alzheimer's disease (AD). Aβ42 oligomer rather than monomer is toxic to neuronal cells and can directly bind to LilrB2, resulting in synaptic loss and cognitive impairment in the development of AD. Therefore, uncovering the mechanism of interaction between Aβ42 oligomer and LilrB2 becomes the first step to obtain a clear drug target and specific binding sites. Herein, a tetracoordinated mechanism for the Aβ oligomer-LilrB2 binding was first put forward by employing Aβ42 dimer mimic-antiparallel copies of Aβ42 core fragment 16KLVFFA21, to bind LilrB2 as models, in which four key residues (F5/F6/L12/F14) in the Aβ42 mimic are bound strongly with LilrB2 residue(s) or accommodated by four hydrophobic cavities in LilrB2 to generate a stable complex. Bi-dentate binding, however, cannot keep the complex Aβ42 mimic-LilrB2 stable. The inhibitor fluspirilene can disturb the binding of four key residues of Aβ42 to LilrB2, justifying the tetracoordinated zipper mechanism on the other hand.

LBA02-12 RBFOX2 COPY NUMBER VARIATION VITIATES URETHRAL CLOSURE CAUSING HYPOSPADIAS

You have accessJournal of UrologyCME1 May 2022LBA02-12 RBFOX2 COPY NUMBER VARIATION VITIATES URETHRAL CLOSURE CAUSING HYPOSPADIAS Victor Ruthig, Fredi Ruiz Rojano, Jeffrey White, Marisol O'Neill, and Dolores Lamb Victor RuthigVictor Ruthig More articles by this author , Fredi Ruiz RojanoFredi Ruiz Rojano More articles by this author , Jeffrey WhiteJeffrey White More articles by this author , Marisol O'NeillMarisol O'Neill More articles by this author , and Dolores LambDolores Lamb More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000002670.12AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: The dosage-sensitive gene, RBFOX2, encodes a RNA binding protein that is a regulator of alternative mRNA splicing. Copy number variations (CNVs) in RBFOX2 cause birth defects in the cardiac and nervous systems. A subset of patients were identified in public databases with genitourinary birth defects, including hydronephrosis and hypospadias, associated with RBFOX2 CNVs. RBOX2 CNVs are more common in patients with GU and CAKUT anomalies (2.4 % of non-syndromic patients with GU birth defects, 0% of our control patients with no GU anomalies and 0.11% of subjects in the general population (Database of Genomic Variants) and 0.06% of patients with anomalies in DECIPHER (p<0.00001; ANOVA). Work by others posited that RBFOX2-mediated splicing is integral in the mesenchymal-to-epithelial transition pathway. In support of this hypothesis, our RNA-sequencing analysis with postnatal penises from Rbfox2-knockout mice, that exhibit CAKUT and/or hypospadias, identified disruption of this pathway. Sequencing analysis revealed evidence of RBFOX2 interaction with sex hormone signal pathways. METHODS: We tested the hypothesis that the developmental origins of a subset of hypospadias is due to RBFOX2 CNVs. Whole exome sequencing identified patients with RBFOX2 CNVs and SNPs. To define the cell type specific expression ofRbfox2, spatiotemporal expression was defined over a fetal time course of mouse penises before and after sex determination of the genital tubercle. Fluorescent in situ hybridization and immunofluorescent whole mount samples were imaged using confocal microscopy. RESULTS: Whole exome sequencing data confirmed in patients with RBFOX2 CNV and damaging SNPs, that these variants were a root cause for lower tract genitourinary anomalies, as well as CAKUT, cardiac defects, intellectual disabilities and head deformities. Imaging experiments defined Rbfox2 expression after sex determination of the murine male genital tubercle. Rbfox2 expression is first confined to the peri-urethral space of the developing penis. In this region, the most abundant urethral RBFOX2 protein signal travels distally starting at the base of the penis as a urethral ring of signal that halts at the junction of the penile body and glans. The glans is encased with an epithelial layer of cells that are strongly RBFOX2-positive. These cells aggregate at the site of glandular urethra formation. Most RBFOX2-positive glandular epithelial cells co-express androgen receptor. The preputial folds have a similar epithelial net of RBFOX2- and androgen receptor-positive cells. CONCLUSIONS: The coincident locations of RBFOX2 signal during urethral formation and development of hypospadias when Rbfox2 is deleted, implicate RBFOX2 as a molecular player in the double zipper mechanism of urethral formation and closure. The more peripheral co-expression of RBFOX2 and androgen receptor in the glandular and preputial epithelium may be part of a RBFOX2-mediated balancing of androgen and estrogen signaling. The hypospadias that is observed when Rbfox2 is deleted would then, at least partly, be due to resultant favoring of the feminization pathway. Source of Funding: AUA/UCF Research Scholar Award to JW; NIH-R01DK078121 and Frederick J. and Theresa Dow Wallace Fund of the New York Community Trust to DJL; NIH-T32DK007763 to DJL for MO © 2022 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 207Issue Supplement 5May 2022Page: e1046 Advertisement Copyright & Permissions© 2022 by American Urological Association Education and Research, Inc.MetricsAuthor Information Victor Ruthig More articles by this author Fredi Ruiz Rojano More articles by this author Jeffrey White More articles by this author Marisol O'Neill More articles by this author Dolores Lamb More articles by this author Expand All Advertisement PDF DownloadLoading ...

The Zipperator! A Novel Model to Simulate Penile Zipper Entrapment.

The Zipperator! A Novel Model to Simulate Penile Zipper Entrapment.

Structural Diversities of Lectins Binding to the Glycosphingolipid Gb3.

Glycolipids are present on the surfaces of all living cells and thereby represent targets for many protein receptors, such as lectins. Understanding the interactions between lectins and glycolipids is essential for investigating the functions of lectins and the dynamics of glycolipids in living membranes. This review focuses on lectins binding to the glycosphingolipid globotriaosylceramide (Gb3), an attractive host cell receptor, particularly for pathogens and pathogenic products. Shiga toxin (Stx), from Shigella dysenteriae or Escherichia coli, which is one of the most virulent bacterial toxins, binds and clusters Gb3, leading to local negative membrane curvature and the formation of tubular plasma membrane invaginations as the initial step for clathrin-independent endocytosis. After internalization, it is embracing the retrograde transport pathway. In comparison, the homotetrameric lectin LecA from Pseudomonas aeruginosa can also bind to Gb3, triggering the so-called lipid zipper mechanism, which results in membrane engulfment of the bacterium as an important step for its cellular uptake. Notably, both lectins bind to Gb3 but induce distinct plasma membrane domains and exploit mainly different transport pathways. Not only, several other Gb3-binding lectins have been described from bacterial origins, such as the adhesins SadP (from Streptococcus suis) and PapG (from E. coli), but also from animal, fungal, or plant origins. The variety of amino acid sequences and folds demonstrates the structural versatilities of Gb3-binding lectins and asks the question of the evolution of specificity and carbohydrate recognition in different kingdoms of life.

The Gb3-enriched CD59/flotillin plasma membrane domain regulates host cell invasion by Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa has gained precedence over the years due to its ability to develop resistance to existing antibiotics, thereby necessitating alternative strategies to understand and combat the bacterium. Our previous work identified the interaction between the bacterial lectin LecA and its host cell glycosphingolipid receptor globotriaosylceramide (Gb3) as a crucial step for the engulfment of P. aeruginosa via the lipid zipper mechanism. In this study, we define the LecA-associated host cell membrane domain by pull-down and mass spectrometry analysis. We unraveled a predilection of LecA for binding to saturated, long fatty acyl chain-containing Gb3 species in the extracellular membrane leaflet and an induction of dynamic phosphatidylinositol (3,4,5)-trisphosphate (PIP3) clusters at the intracellular leaflet co-localizing with sites of LecA binding. We found flotillins and the GPI-anchored protein CD59 not only to be an integral part of the LecA-interacting membrane domain, but also majorly influencing bacterial invasion as depletion of either of these host cell proteins resulted in about 50% reduced invasiveness of the P. aeruginosa strain PAO1. In summary, we report that the LecA-Gb3 interaction at the extracellular leaflet induces the formation of a plasma membrane domain enriched in saturated Gb3 species, CD59, PIP3 and flotillin thereby facilitating efficient uptake of PAO1.

Insights into ADAMTS13 structure: impact on thrombotic thrombocytopenic purpura diagnosis and management.

Fundamental knowledge on the role of a disintegrin and metalloprotease with thrombospondin type one repeats, member 13 (ADAMTS13) has been crucial to better understand the pathophysiology of the rare and life-threatening disease thrombotic thrombocytopenic purpura (TTP). ADAMTS13 works through a molecular zipper mechanism to proteolyze its substrate von Willebrand factor (VWF). Recent insights into the structure and function of ADAMTS13 led to the identification of an allosteric activation mechanism. Therefore, ADAMTS13 is roughly folded in two in which the N-terminal spacer (S) domain and C-terminal T7-CUB2 domains interact to adopt a closed conformation. Upon substrate binding, ADAMTS13 adopts an open conformation in which the S-T7-CUB2 interaction is abrogated to further position VWF towards the catalytic cleft, inducing activation of the latent metalloprotease domain and resulting in cleavage of VWF. Unravelling the structure function relationship of ADAMTS13 helped identifying open ADAMTS13 as a novel and unique biomarker for immune-mediated TTP (iTTP). This novel biomarker has potential in the diagnosis, treatment and follow-up of iTTP. In this review, the most recent findings on the structure and working mechanism of ADAMTS13 are addressed. In addition, how those findings led to the identification of a novel biomarker, and how this novel biomarker could have an impact on the diagnosis, management and follow-up of iTTP patients are discussed.

Domain zipping and unzipping modulates TRPM4's properties in human cardiac conduction disease.

The transient receptor potential melastatin 4 (TRPM4) is a Ca2+ -activated nonselective cation channel linked to human cardiac diseases. The human mutation K914R within TRPM4's S4-S5 linker was identified in patients with atrioventricular block. During UV-flash-mediated Ca2+ transients, TRPM4K914R generated a threefold augmented membrane current concomitant with 2 to 3-fold slowed down activation and deactivation kinetics resulting in excessive membrane currents during human cardiac action potentials. Mutagenesis of K914 paired with molecular modeling suggested the importance of the nanoscopic interface between the S4-S5 linker, the MHR4-, and TRP-domain as a major determinant for TRPM4's behavior. Rational mutagenesis of an interacting amino acid (R1062Q) in the TRP domain was able to offset K914R`s gain-of-function by zipping and unzipping of this nanoscopic interface. In conclusion, repulsion and attraction between the amino acids at positions 914 and 1062 alters the flexibility of the nanoscopic interface suggesting a zipping and unzipping mechanism that modulates TRPM4's functions. Pharmacological modulation of this intramolecular mechanism might represent a novel therapeutic strategy for the management of TRPM4-mediated cardiac diseases.

Domain Zipping and Unzipping Modulates TRPM4's Properties in Human Cardiac Conduction Disease

The transient receptor potential melastatin 4 (TRPM4) is a Ca2+ -activated nonselective cation channel linked to human cardiac diseases. The human mutation K914R within TRPM4's S4-S5 linker was identified in patients with atrioventricular block. During UV-flash-mediated Ca2+ transients, TRPM4K914R generated a threefold augmented membrane current concomitant with 2 to 3-fold slowed down activation and deactivation kinetics resulting in excessive membrane currents during human cardiac action potentials. Mutagenesis of K914 paired with molecular modeling suggested the importance of the nanoscopic interface between the S4-S5 linker, the MHR4-, and TRP-domain as a major determinant for TRPM4's behavior. Rational mutagenesis of an interacting amino acid (R1062Q) in the TRP domain was able to offset K914R`s gain-of-function by zipping and unzipping of this nanoscopic interface. In conclusion, repulsion and attraction between the amino acids at positions 914 and 1062 alters the flexibility of the nanoscopic interface suggesting a zipping and unzipping mechanism that modulates TRPM4's functions. Pharmacological modulation of this intramolecular mechanism might represent a novel therapeutic strategy for the management of TRPM4-mediated cardiac diseases.

Simulations Reveal Multiple Intermediates in the Unzipping Mechanism of Neuronal SNARE Complex

The assembling of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor protein complex is a fundamental step in neuronal exocytosis, and it has been extensively studied in the last two decades. Yet, many details of this process remain inaccessible with the current experimental space and time resolution. Here, we study the zipping mechanism of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex computationally by using a coarse-grained model. We explore the different pathways available and analyze their dependence on the computational model employed. We reveal and characterize multiple intermediate states, in agreement with previous experimental findings. We use our model to analyze the influence of single-residue mutations on the thermodynamics of the folding process.

Salmonella Typhimurium Invalidated for the Three Currently Known Invasion Factors Keeps Its Ability to Invade Several Cell Models.

To establish an infection, Salmonella has to interact with eukaryotic cells. Invasion of non-phagocytic cells (i.e., epithelial, fibroblast and endothelial cells) involves either a trigger or a zipper mechanism mediated by the T3SS-1 or the invasin Rck, respectively. Another outer membrane protein, PagN, was also implicated in the invasion. However, other unknown invasion factors have been previously suggested. Our goal was to evaluate the invasion capability of a Salmonella Typhimurium strain invalidated for the three known invasion factors. Non-phagocytic cell lines of several animal origins were tested in a gentamicin protection assay. In most cells, we observed a drastic decrease in the invasion rate between the wild-type and the triple mutant. However, in five cell lines, the triple mutant invaded cells at a similarly high level to the wild-type, suggesting the existence of unidentified invasion factors. For the wild-type and the triple mutant, scanning-electron microscopy, confocal imaging and use of biochemical inhibitors confirmed their cellular uptake and showed a zipper-like mechanism of internalization involving both clathrin- and non-clathrin-dependent pathways. Despite a functional T3SS-1, the wild-type bacteria seemed to use the same entry route as the mutant in our cell model. All together, these results demonstrate the existence of unknown Salmonella invasion factors, which require further characterization.

Molecular Recognition of Ice by Fully Flexible Molecules

Cold acclimatized organisms produce antifreeze proteins that prevent ice growth and recrystallization at subfreezing conditions. Flatness and rigidity of the ice-binding sites of antifreeze proteins are considered key for their recognition of ice. However, the most potent synthetic ice recrystallization inhibitor (IRI) found to date is poly(vinyl alcohol) (PVA), a fully flexible molecule. The ability to tune the architecture and functionalization of PVA makes it a promising candidate to replace antifreeze proteins in industrial applications ranging from cryopreservation of organs to deicing of turbine blades. However, an understanding of how does PVA recognize ice remains elusive, hampering the design of more effective IRIs. Here we use large-scale molecular simulations to elucidate the mechanism by which PVA recognizes ice. We find that the polymer selectively binds to the prismatic faces of ice through a cooperative zipper mechanism. The binding is driven by hydrogen bonding, facilitated by distance mat...