Microbead analysis of cell binding to immobilized lectin: an alternative to microarrays in the development of carbohydrate drugs and diagnostic tests

Microbead analysis of cell binding to immobilized lectin. Part II: Quantitative kinetic profile assay for possible identification of anti-infectivity and anti-cancer reagents

There has been a re-emergence of the use of lectins in a variety of therapeutic venues. In addition lectins are often responsible for the binding of pathogens to cells and for cancer cell clumping that increases their escape from body defenses. It is important to define precisely the activity of inhibitors of lectin-binding that may be used in anti-infection and anti-cancer therapeutics. Here we describe a kinetic assay that measures the activity of saccharide inhibitors of lectin binding using a model system of yeast (Saccharomyces cerevisiae) and lectin (Concanavalin A, Con A) derivatized agarose microbeads that mimics pathogen-cell binding. We show that old methods (part I of this study) used to identify inhibitor activity using only one sugar concentration at one time point can easily provide wrong information about inhibitor activity. We assess the activity of 4 concentrations of 10 saccharides at 4 different times in 400 trials and statistically evaluate the results. We show that d-melezitose is the best inhibitor of yeast binding to the lectin microbeads. These results, along with physical chemistry studies, provide a solid foundation for the development of drugs that may be useful in anti-infectivity and anti-cancer therapeutics.

Activation of G-protein-coupled receptors in cell-derived plasma membranes supported on porous beads

G-protein-coupled receptors (GPCRs) are ubiquitous mediators of signal transduction across cell membranes and constitute a very important class of therapeutic targets. In order to study the complex biochemical signaling network coupling to the intracellular side of GPCRs, it is necessary to engineer and control the downstream signaling components, which is difficult to realize in living cells. We have developed a bioanalytical platform enabling the study of GPCRs in their native membrane transferred inside-out from live cells to lectin-coated beads, with both membrane sides of the receptor being accessible for molecular interactions. Using heterologously expressed adenosine A(2A) receptor carrying a yellow fluorescent protein, we showed that the tethered membranes comprised fully functional receptors in terms of ligand and G protein binding. The interactions between the different signaling partners during the formation and subsequent dissociation of the ternary signaling complex on single beads could be observed in real time using multicolor fluorescence microscopy. This approach of tethering inside-out native membranes accessible from both sides is straightforward and readily applied to other transmembrane proteins. It represents a generic platform suitable for ensemble as well as single-molecule measurements to investigate signaling processes at plasma membranes.

A glycobiology review: carbohydrates, lectins and implications in cancer therapeutics

This review is intended for general readers who would like a basic foundation in carbohydrate structure and function, lectin biology, and the implications of glycobiology in human health and disease, particularly in cancer therapeutics. These topics are among the hundreds included in the field of glycobiology and are treated here because they form the cornerstone of glycobiology or the focus of many advances in this rapidly expanding field.

Carbohydrate-based experimental therapeutics for cancer, HIV/AIDS and other diseases

This review, primarily for general readers, briefly presents experimental approaches to therapeutics of cancer, HIV/AIDS and various other diseases based on advances in glycobiology and glycochemistry. Experimental cancer and HIV/AIDS vaccines are being developed in attempts to overcome weak immunological responses to carbohydrate-rich surface antigens using carriers, adjuvants and novel carbohydrate antigen constructs. Current carbohydrate-based vaccines are used for typhus, pneumonia, meningitis; vaccines for anthrax, malaria and leishmaniasis are under development. The link between O-linked beta-N-acetylglucosamine glycosylation and protein phosphorylation in diseases including diabetes and Alzheimer's disease is also explored. Carbohydrate-associated drugs that are in current use or under development, such as heparan sulfate binders, lectins, acarbose, aminoglycosides, tamiflu and heparin, and technologies using carbohydrate and lectin microarrays that offer improved diagnostic and drug development possibilities, are described. Advances in carbohydrate synthesis, analysis and manipulation through the emerging fields of glycochemistry and glycobiology are providing new approaches to disease therapeutics.