Carbohydrates as recognition molecules in infection and immunity

Consideration of host-parasite interactions encompasses a wide range of phenomena from adhesion to epithelial surfaces to interactions with cells of the immune system. This review focuses on the role of carbohydrates as recognition molecules in these complex interactions. The abundant glycoproteins and glycolipids of cell surfaces of both prokaryotic and eukaryotic cells have the ability to exist in a variety of spatial configurations through alpha- and beta-linkages and the formation of branched structures. This ability carries with it the opportunity of acting as informational molecules greater than that possible for proteins or nucleic acids. The blood group substances are probably the best characterized of these carbohydrate containing molecules. Whilst at present a detailed understanding of the importance of these molecules in host-parasite interaction is lacking, the material covered in this discussion emphasizes the way in which carbohydrate based recognition has been shown to be involved and may provide the basis for further understanding.     

Carbohydrate-carbohydrate interactions in adhesion

Cell-cell interactions play an important role in the development, maintenance, and pathogenesis of tissues. They are highly dynamic processes which include migration, recognition, signaling, adhesion, and finally attachment. Cells on their pathway to a final location have to pass and interact with their substratum formed of matrix and cell layers. Testing and recognition are important keys for the proper result of tissue formation. They can, however, also lead to diseases when they are misused in pathological situations, by microorganisms or malignant cells, for instance. Carbohydrates, which are the most prominent surface-exposed structures, must play an important role as recognition molecules in such processes. The rich variability of carbohydrate sequences which cell surfaces can present to lectins, adhesion molecules, and other ligands creates a refined pattern of potential attachment sites. The subtle control of the surface presentation density can provide variations in attachment strength. Not only the carbohydrate sequences but also the fact that carbohydrates can be branched while proteins cannot and that the oligosaccharide chains can be attached to the protein backbone in different densities and patterns will create yet more interaction possibilities. Maximal use of the combinatorial richness of carbohydrate molecules would be made when carbohydrate sequences could interact with other carbohydrate sequences. Such interactions have only very rarely been considered for biochemically and biologically relevant situations since they are difficult to measure. A few are known and will be summarized here with the hope that this wealth of possible chemical interactions may be considered more and more by surface cell biochemists when analyzing fine tuning in cellular interactions. © 1996 Wiley-Liss, Inc.     

Biofunctionalization of biomaterials for accelerated in situ endothelialization: a review

The higher patency rates of cardiovascular implants, including vascular bypass grafts, stents, and heart valves are related to their ability to inhibit thrombosis, intimal hyperplasia, and calcification. In native tissue, the endothelium plays a major role in inhibiting these processes. Various bioengineering research strategies thereby aspire to induce endothelialization of graft surfaces either prior to implantation or by accelerating in situ graft endothelialization. This article reviews potential bioresponsive molecular components that can be incorporated into (and/or released from) biomaterial surfaces to obtain accelerated in situ endothelialization of vascular grafts. These molecules could promote in situ endothelialization by the mobilization of endothelial progenitor cells (EPC) from the bone marrow, encouraging cell-specific adhesion (endothelial cells (EC) and/or EPC) to the graft and, once attached, by controlling the proliferation and differentiation of these cells. EC and EPC interactions with the extracellular matrix continue to be a principal source of inspiration for material biofunctionalization, and therefore, the latest developments in understanding these interactions will be discussed.     

‘Bio-nano interactions: new tools,insights and impacts’: summary of the Royal Society discussion meeting

Bio-nano interactions can be defined as the study of interactions between nanoscale entities and biological systems such as, but not limited to, peptides, proteins, lipids, DNA and other biomolecules, cells and cellular receptors and organisms including humans. Studying bio-nano interactions is particularly useful for understanding engineered materials that have at least one dimension in the nanoscale. Such materials may consist of discrete particles or nanostructured surfaces. Much of biology functions at the nanoscale; therefore, our ability to manipulate materials such that they are taken up at the nanoscale, and engage biological machinery in a designed and purposeful manner, opens new vistas for more efficient diagnostics, therapeutics (treatments) and tissue regeneration, so-called nanomedicine. Additionally, this ability of nanomaterials to interact with and be taken up by cells allows nanomaterials to be used as probes and tools to advance our understanding of cellular functioning. Yet, as a new technology, assessment of the safety of nanomaterials, and the applicability of existing regulatory frameworks for nanomaterials must be investigated in parallel with development of novel applications. The Royal Society meeting ‘Bio-nano interactions: new tools, insights and impacts'' provided an important platform for open dialogue on the current state of knowledge on these issues, bringing together scientists, industry, regulatory and legal experts to concretize existing discourse in science law and policy. This paper summarizes these discussions and the insights that emerged.     

Restricted mobility of side chains on concave surfaces of solenoid proteins may impart heightened potential for intermolecular interactions

Significant progress has been made in the determination of the protein structures with their number today passing over a hundred thousand structures. The next challenge is the understanding and prediction of protein–protein and protein–ligand interactions. In this work we address this problem by analyzing curved solenoid proteins. Many of these proteins are considered as “hub molecules” for their high potential to interact with many different molecules and to be a scaffold for multisubunit protein machineries. Our analysis of these structures through molecular dynamics simulations reveals that the mobility of the side‐chains on the concave surfaces of the solenoids is lower than on the convex ones. This result provides an explanation to the observed preferential binding of the ligands, including small and flexible ligands, to the concave surface of the curved solenoid proteins. The relationship between the landscapes and dynamic properties of the protein surfaces can be further generalized to the other types of protein structures and eventually used in the computer algorithms, allowing prediction of protein–ligand interactions by analysis of protein surfaces . Proteins 2015; 83:1654–1664. © 2015 Wiley Periodicals, Inc.     

Induction and suppression of RNA silencing: insights from viral infections

In eukaryotes, small RNA molecules engage in sequence-specific interactions to inhibit gene expression by RNA silencing. This process fulfils fundamental regulatory roles, as well as antiviral functions, through the activities of microRNAs and small interfering RNAs. As a counter-defence mechanism, viruses have evolved various anti-silencing strategies that are being progressively unravelled. These studies have not only highlighted our basic understanding of host-parasite interactions, but also provide key insights into the diversity, regulation and evolution of RNA-silencing pathways.     

Development of a ligand blot assay using biotinylated live cells

Adhesive interactions between cells are critical to a variety of processes, including host-pathogen relationships. The authors have developed a new technique for the observation of binding interactions in which molecules obtained from excised tissues are resolved by gel electrophoresis and transferred to a membrane. Biotinylated live cells are then kept in contact with that membrane, and their interactions with proteins of interest are detected by peroxidase-labeled streptavidin, followed by a biotin-streptavidin detection system. The adhesion proteins can eventually be identified by cutting the relevant band(s) and performing mass spectrometry or other amino acid-sequencing methods. The technique described here allows for the identification of both known and novel adhesion molecules capable of binding to live cells, among a complex mixture and without previous isolation or purification. This is especially important for the analysis of host-parasite interactions and may be extended to other types of cell-cell interactions.     

Characterization of protein–glycolipid recognition at the membrane bilayer

A growing number of important molecular recognition events are being shown to involve the interactions between proteins and glycolipids. Glycolipids are molecules in which one or more monosaccharides are glycosidically linked to a lipid moiety. The lipid moiety is generally buried in the cell membrane or other bilayer, leaving the oligosaccharide moiety exposed but in close proximity to the bilayer surface. This presents a unique environment for protein–carbohydrate interactions, and studies to determine the influence of the bilayer on these phenomena are in their infancy. One important property of the bilayer is the ability to orient and cluster glycolipid species, as strong interactions in biological systems are often achieved through multivalency arising from the simultaneous association of two or more proteins and receptors. This is especially true of protein–carbohydrate binding because of the unusually low affinities that characterize the monovalent interactions. More recent studies have also shown that the composition of the lipid bilayer is a critical parameter in protein–glycolipid recognition. The fluidity of the bilayer allows for correct geometric positioning of the oligosaccharide head group relative to the binding sites on the protein. In addition, there are activity‐based and structural data demonstrating the impact of the bilayer microenvironment on the modulation of oligosaccharide presentation. The use of model membranes in biosensor‐based methods has supplied decisive evidence of the importance of the membrane in receptor presentation. These data can be correlated with three‐dimensional structural information from X‐ray <?tw=98%>crystallography, NMR, and molecular mechanics to provide insight into specific protein–carbohydrate inter‐­actions at the bilayer. Copyright © 1999 National Research Council Canada and John Wiley & Sons, Ltd.     

Cryptosporidium excystation and invasion: getting to the guts of the matter

Cryptosporidium parvum excystation and host cell invasion have been characterized in some detail ultrastructurally. However, until recently, the biochemical and molecular basis of host-parasite interactions and parasite- and host-specific molecules involved in excystation, motility and host cell invasion have been poorly understood. This article describes our understanding of Cryptosporidium excystation and the events leading to host cell invasion, and draws from information available about these processes in other apicomplexans. Many questions remain but, once the specific mechanisms are identified, they could prove to be novel targets for drug delivery.     

Food-environment mediates the outcome of specific interactions between a bumblebee and its trypanosome parasite

Specific host-parasite interactions, where the outcome of exposure to a parasite depends upon the genotypic identity of both parties, have implications for understanding host-parasite coevolution and patterns of genetic diversity. Thus, grasping the extent to which these interactions are mediated by environmental changes in a spatially and temporally heterogeneous world is vital. In this study, it is shown that the environment can influence specific host-parasite interactions in the well-studied system of the bumblebee Bombus terrestris and its trypanosome parasite Crithidia bombi. Naturally relevant variation in the quality of the food environment formed a three-way interaction with both host and parasite identity in determining the outcome of infection, with regard to the resistance of the host and the transmission of the parasite. The demonstration of such a host-genotype by parasite-genotype by environment interaction (G(H) x G(P) x E) shows the importance of considering environmental variation when investigating host-parasite interactions. Moreover, such interactions may to some extent explain levels of genetic diversity in natural host-parasite systems owing to the fact that they will create selection mosaics when environments are heterogeneous.     

Myelin glycosphingolipids,galactosylceramide and sulfatide,participate in carbohydrate–carbohydrate interactions between apposed membranes and may form glycosynapses between oligodendrocyte and/or myelin membranes

Glycosphingolipids (GSLs) can interact with each other by homotypic or heterotypic trans carbohydrate–carbohydrate interactions across apposed membranes, resulting in cell–cell adhesion. This interaction can also provide an extracellular signal which is transmitted to the cytosolic side, thus forming a glycosynapse between two cells. The two major GSLs of myelin, galactosylceramide (GalC) and its sulfated form, galactosylceramide I³-sulfate (SGC), are an example of a pair of GSLs which can participate in these trans carbohydrate–carbohydrate interactions and trigger transmembrane signaling. These GSLs could interact across apposed oligodendrocyte membranes at high cell density or when a membranous process of a cell contacts itself as it wraps around the axon. GalC and SGC also face each other in the apposed extracellular surfaces of the multilayered myelin sheath. Communication between the myelin sheath and the axon regulates both axonal and myelin function and is necessary to prevent neurodegeneration. Participation of transient GalC and SGC interactions in glycosynapses between the apposed extracellular surfaces of mature myelin might allow transmission of signals throughout the myelin sheath and thus facilitate myelin-axonal communication.     

Island and taxon effects in parasitism revisited: avian malaria in the Lesser Antilles

We identify and describe the distribution of 12 genetically distinct malaria parasite lineages over islands and hosts in four common passerine birds in the Lesser Antilles. Combined parasite prevalence demonstrates strong host effects, little or no island effect, and a significant host-times-island interaction, indicating independent outcomes of host-parasite infections among island populations of the same host species. Host- and/or island-specific parasite lineages do not explain these host-parasite associations; rather, individual lineages themselves demonstrate the same type of independent interactions. Unlike overall prevalence, individual parasite lineages show considerable geographic structure (i.e., island effects) as well as species effects indicating that parasite lineages are constrained in their ability to move between hosts and locations. Together, our results suggest an upper limit to the number of host individuals that malaria parasites, as a community, can infect. Within this limit, however, the relative frequency of the different lineages varies reflecting fine scale interactions between host and parasite populations. Patterns of host-parasite associations within this system suggest both historical co-evolution and ecologically dynamic and independent host-parasite interactions.     

Extracellular Vesicles from Parasitic Helminths Contain Specific Excretory/Secretory Proteins and Are Internalized in Intestinal Host Cells

The study of host-parasite interactions has increased considerably in the last decades, with many studies focusing on the identification of parasite molecules (i.e. surface or excretory/secretory proteins (ESP)) as potential targets for new specific treatments and/or diagnostic tools. In parallel, in the last few years there have been significant advances in the field of extracellular vesicles research. Among these vesicles, exosomes of endocytic origin, with a characteristic size ranging from 30–100 nm, carry several atypical secreted proteins in different organisms, including parasitic protozoa. Here, we present experimental evidence for the existence of exosome-like vesicles in parasitic helminths, specifically the trematodes Echinostoma caproni and Fasciola hepatica. These microvesicles are actively released by the parasites and are taken up by host cells. Trematode extracellular vesicles contain most of the proteins previously identified as components of ESP, as confirmed by proteomic, immunogold labeling and electron microscopy studies. In addition to parasitic proteins, we also identify host proteins in these structures. The existence of extracellular vesicles explains the secretion of atypical proteins in trematodes, and the demonstration of their uptake by host cells suggests an important role for these structures in host-parasite communication, as described for other infectious agents.     

Genes required for the common miracle of fertilization in Caenorhabditis elegans

Fertilization involves multiple layers of sperm-egg interactions that lead to gamete fusion and egg activation. There must be specific molecules required for these interactions. The challenge is to determine the identity of the genes encoding these molecules and how their protein products function. The nematode worm Caenorhabditis elegans has emerged as an efficient model system for gene discovery and understanding the molecular mechanisms of fertilization. The primary advantage of the C. elegans system is the ability to isolate and maintain mutants that affect sperm or eggs and no other cells. In this review we describe progress and challenges in the analysis of genes required for gamete interactions and egg activation in the worm.     

In-vivo Detection of Protein-protein Interactions on Micro-patterned Surfaces

Unraveling the interaction network of molecules in-vivo is key to understanding the mechanisms that regulate cell function and metabolism. A multitude of methodological options for addressing molecular interactions in cells have been developed, but most of these methods suffer from being rather indirect and therefore hardly quantitative. On the contrary, a few high-end quantitative approaches were introduced, which however are difficult to extend to high throughput. To combine high throughput capabilities with the possibility to extract quantitative information, we recently developed a new concept for identifying protein-protein interactions (Schwarzenbacher et al., 2008). Here, we describe a detailed protocol for the design and the construction of this system which allows for analyzing interactions between a fluorophore-labeled protein ("prey") and a membrane protein ("bait") in-vivo. Cells are plated on micropatterned surfaces functionalized with antibodies against the bait exoplasmic domain. Bait-prey interactions are assayed via the redistribution of the fluorescent prey. The method is characterized by high sensitivity down to the level of single molecules, the capability to detect weak interactions, and high throughput capability, making it applicable as screening tool.     

Bioactive molecules of Taenia solium metacestode, a causative agent of neurocysticercosis

Neurocysticercosis (NC), an infection of the CNS with Taenia solium metacestode, exemplifies formidable public health concerns associated with significant morbidity and mortality. The disease is a complex phenomenon involving molecular cell biological cross-talks between the parasite and human host. To effectively combat NC, specific diagnosis and proper management are prerequisites. Bioactive molecules implicated in host-parasite interactions and parasitic homeostasis should be elucidated. This article provides an overview of currently available serological biomarkers, especially those comprising low-molecular-weight proteins, and discusses available immunoproteomics for identification of such molecules. T. solium metacestode bioactive molecules, which might be critically implicated in the progression of NC disease, are summarized. Comprehensive understanding of the biochemical properties and biological functions of bioactive molecules may contribute to the development of novel intervention strategies against NC.     

Advances in Fasciola hepatica research using ‘omics’ technologies

The liver fluke Fasciola hepatica is an economically important pathogen of livestock worldwide, as well as being an important neglected zoonosis. Parasite control is reliant on the use of drugs, particularly triclabendazole, which is effective against multiple parasite stages. However, the spread of parasites resistant to triclabendazole has intensified the pursuit for novel control strategies. Emerging 'omics' technologies are helping advance our understanding of liver fluke biology, specifically the molecules that act at the host-parasite interface and are central to infection, virulence and long-term survival within the definitive host. This review discusses the technological sequencing advances that have facilitated the unbiased analysis of liver fluke biology, resulting in an extensive range of ‘omics’ datasets. In addition, we highlight the ‘omics’ studies of host responses to F. hepatica infection that, when combined with the parasite datasets, provide the opportunity for integrated analyses of host-parasite interactions. These extensive datasets will form the foundation for future in-depth analysis of F. hepatica biology and development, and the search for new drug or vaccine interventions.     

The receptor function of galactosyltransferase during cellular interactions

Summary The molecular mechanisms that underly cellular interactions during development are still poorly understood. There is reason to believe that complex glycoconjugates participate in cellular interactions by binding to specific cell surface receptors. One class of carbohydrate binding proteins that could serve as receptors during cellular interactions are the glycosyltransferases. Glycosyltransferases have been detected on a variety of cell surfaces, and evidence suggests that they may participate during cellular interactions by binding their specific carbohydrate substrates on adjacent cells or in extracellular matrix (see Refs. 1–4 for review).This review will focus on the receptor function of galactosyltransferase, in particular, during fertilization, embryonic cell adhesion and migration, limb bud morphogenesis, immune recognition and growth control. In many of these systems, the galactosyltransferase substrate has been characterized as a novel, large molecular weight glycoconjugate composed of repeating N-acetyllactosamine residues. The function of surface galactosyl-transferase during cellular interactions has been examined with genetic and biochemical probes, including the T/t-complex morphogenetic mutants, enzyme inhibitors, enzyme modifiers, and competitive substrates. Collectively, these studies suggest that in the mouse, surface galactosyltransferase is under the genetic control of the T/t-complex, and participates in multiple cellular interactions during development by binding to its specific lactosaminoglycan substrate.     

Atomic force microscopy measurements. Measurements of binding strength between a single pair of molecules in physiological solutions

Atomic force microscopy (AFM) measurements of intermolecular binding strength between a single pair of complementary cell adhesion molecules in physiological solutions provided the first quantitative evidence for their cohesive function. This novel AFM based nanobiotechnology opens a molecular mechanic approach for studying structure to function related properties of any type of individual biological macromolecules. The presented example of Porifera cell adhesion glyconectin proteoglycans showed that homotypic carbohydrate to carbohydrate interactions between two primordial proteogylycans can hold the weight of 1600 cells. Thus, glyconectin type carbohydrates, as the most peripheral cell surface molecules of sponges (today’s simplest living Metazoa), are proposed to the primary cell adhesive molecules essential for the evolution of the multicellularity.     

肿瘤细胞粘附、迁移与转移的相关性

肿瘤细胞的粘附、迁移能力与癌转移密切相关. 细胞粘附分子选择素、整合素、免疫球蛋白超家族及钙粘素介导同型或异型细胞间以及细胞与基质间的粘附,其在肿瘤细胞表面表达数量或分布方式的改变直接或间接影响着转移潜能,是肿瘤细胞从原发瘤脱落以及着床的关键性环节.肿瘤细胞的迁移能力被认为是癌转移的限速环节.一般情况下,肿瘤细胞在体内或体外的迁移能力与其转移潜能呈正相关性,肿瘤细胞通过对迁移刺激物的趋化性及趋触性应答而完成向远离器官的转移,其具体分子机制目前还不清楚.