Phages are now acknowledged as the most abundant microorganisms on the planet and are also possibly the most diversified. This diversity is mostly driven by their dynamic adaptation when facing selective pressure such as phage resistance mechanisms, which are widespread in bacterial hosts. When infecting bacterial cells, phages face a range of antiviral mechanisms, and they have evolved multiple tactics to avoid, circumvent or subvert these mechanisms in order to thrive in most environments. In this Review, we highlight the most important antiviral mechanisms of bacteria as well as the counter-attacks used by phages to evade these systems.

Bacteriophage resistance mechanisms.

Heparin, a sulfated polysaccharide belonging to the family of glycosaminoglycans, has numerous important biological activities, associated with its interaction with diverse proteins. Heparin is widely used as an anticoagulant drug based on its ability to accelerate the rate at which antithrombin inhibits serine proteases in the blood coagulation cascade. Heparin and the structurally related heparan sulfate are complex linear polymers comprised of a mixture of chains of different length, having variable sequences. Heparan sulfate is ubiquitously distributed on the surfaces of animal cells and in the extracellular matrix. It also mediates various physiologic and pathophysiologic processes. Difficulties in evaluating the role of heparin and heparan sulfate in vivo may be partly ascribed to ignorance of the detailed structure and sequence of these polysaccharides. In addition, the understanding of carbohydrate-protein interactions has lagged behind that of the more thoroughly studied protein-protein and protein-nucleic acid interactions. The recent extensive studies on the structural, kinetic, and thermodynamic aspects of the protein binding of heparin and heparan sulfate have led to an improved understanding of heparin-protein interactions. A high degree of specificity could be identified in many of these interactions. An understanding of these interactions at the molecular level is of fundamental importance in the design of new highly specific therapeutic agents. This review focuses on aspects of heparin structure and conformation, which are important for its interactions with proteins. It also describes the interaction of heparin and heparan sulfate with selected families of heparin-binding proteins.

http://www-heparin.rpi.edu/main/files/papers/4f1623c54d6ab5.21304086.pdf

Heparin-protein interactions

The human parvovirus adeno-associated virus (AAV) infects a broad range of cell types, including human, nonhuman primate, canine, murine, and avian. Although little is known about the initial events of virus infection, AAV is currently being developed as a vector for human gene therapy. Using defined mutant CHO cell lines and standard biochemical assays, we demonstrate that heparan sulfate proteoglycans mediate both AAV attachment to and infection of target cells. Competition experiments using heparin, a soluble receptor analog, demonstrated dose-dependent inhibition of AAV attachment and infection. Enzymatic removal of heparan but not chondroitin sulfate moieties from the cell surface greatly reduced AAV attachment and infectivity. Finally, mutant cell lines that do not produce heparan sulfate proteoglycans were significantly impaired for both AAV binding and infection. This is the first report that proteoglycan has a role in cellular attachment of a parvovirus. Together, these results demonstrate that membrane-associated heparan sulfate proteoglycan serves as the viral receptor for AAV type 2, and provide an explanation for the broad host range of AAV. Identification of heparan sulfate proteoglycan as a viral receptor should facilitate development of new reagents for virus purification and provide critical information on the use of AAV as a gene therapy vector.

Membrane-Associated Heparan Sulfate Proteoglycan Is a Receptor for Adeno-Associated Virus Type 2 Virions

BACKGROUND Humans ingest a multitude of small molecules that are foreign to the body (xenobiotics), including dietary components, environmental chemicals, and pharmaceuticals. The trillions of microorganisms that inhabit our gastrointestinal tract (the human gut microbiota) can directly alter the chemical structures of such compounds, thus modifying their lifetimes, bioavailabilities, and biological effects. Our knowledge of how gut microbial transformations of xenobiotics affect human health is in its infancy, which is surprising given the importance of the gut microbiota. We currently lack an understanding of the extent to which this metabolism varies between individuals, the mechanisms by which these microbial activities influence human biology, and how we might rationally manipulate these reactions. This deficiency stems largely from the difficulty of connecting this microbial chemistry to specific organisms, genes, and enzymes. ADVANCES Over the past several decades, studies of gut microbiota–mediated modification of xenobiotics have revealed that these organisms collectively have a larger metabolic repertoire than human cells. The chemical differences between human and microbial transformations of ingested compounds arise not only from the increased diversity of enzymes present in this complex and variable community but also from the distinct selection pressures that have shaped these activities. For example, whereas host metabolism evolved to facilitate excretion of many xenobiotics from the body, microbial modifications of these compounds and their human metabolites often support microbial growth through provision of nutrients or production of energy. Notably, the chemistry of microbial transformations often opposes or reverses that of host metabolism, altering the pharmacokinetic and pharmacodynamic properties of xenobiotics and associated metabolites. The range of xenobiotics subject to gut microbial metabolism is impressive and expanding. Gut microbes modify many classes of dietary compounds, including complex polysaccharides, lipids, proteins, and phytochemicals. These metabolic reactions are linked to a variety of health benefits, as well as disease susceptibilities. Gut microbes are also able to transform industrial chemicals and pollutants, altering their toxicities and lifetimes in the body. Similarly, microbial transformations of drugs can change their pharmacokinetic properties, be critical for prodrug activation, and lead to undesirable side effects or loss of efficacy. In the vast majority of cases, the individual microbes and enzymes that mediate these reactions are unknown. Fueled by findings underscoring the relevance of microbial xenobiotic metabolism to human health, scientists are increasingly seeking to discover and manipulate the enzymatic chemistry involved in these transformations. Recent work exploring how gut microbes metabolize the drugs digoxin and irinotecan, as well as the dietary nutrient choline, provides guidance for such investigations. These studies, which combine traditional methods with modern approaches, illustrate how a molecular understanding of gut microbial xenobiotic metabolism can guide hypothesis-driven research into the roles these reactions play in both microbiota and host biology. OUTLOOK We still face a myriad of challenges in understanding the gut microbiota’s contribution to xenobiotic metabolism. It is imperative that we connect the many known microbial transformations with the genes and enzymes responsible for these activities, and knowledge of enzyme mechanism and biochemical logic will facilitate this objective. There also remains a great need to uncover currently unappreciated activities associated with this community. Revealing the full scope of microbially mediated transformations in the gut may give us new insights into the many variable and contradictory studies regarding the effects of diet, pollutants, and drugs on human health. Microbial genes and enzymes will provide both specific targets for manipulation and diagnostic markers that can be incorporated into clinical studies and practice. Ultimately, a molecular understanding of gut microbial xenobiotic metabolism will inform personalized nutrition, toxicology risk assessment, precision medicine, and drug development.

Chemical transformation of xenobiotics by the human gut microbiota

http://cbm.msoe.edu/includes/pdf/smart2013/Review_Hyaluronidase_Eraser.pdf

The magic glue hyaluronan and its eraser hyaluronidase: a biological overview.

Polysaccharide lyases (or eliminases) are a class of enzymes (EC 4.2.2.-) that act to cleave certain activated glycosidic linkages present in acidic polysaccharides. These enzymes act through an eliminase mechanism, rather than through hydrolysis, resulting in unsaturated oligosaccharide products. Acidic polysaccharides are ubiquitous and so are the lyases that degrade them. This review article examines lyases that act on acidic polysaccharides of plant, animal, and microbial origin. These lyases are predominantly of microbial origin and come from a wide variety of both pathogenic and nonpathogenic bacteria and fungi. The lyases discussed include alginate lyase (EC 4.2.2.3), pectin lyase (EC 4.2.2.10), pectate lyase (EC 4.2.2.2), oligogalacturonide lyase (EC 4.2.2.6), exopolygalacturonate lyase (EC 4.2.2.9), chondroitin lyases (EC 4.2.2.4 and EC 4.2.2.5), hyaluronate lyase (EC 4.2.2.1), heparin lyase (EC 4.2.2.7), heparan lyase (EC 4.2.2.8), and other unclassified lyases. This review examines the sources, regulation, purification, and properties of these polysaccharide lyases.

P. M. Galliher

Papers

Polysaccharide lyases