Transport features, reaction kinetics and receptor biomechanics controlling selectin and integrin mediated cell adhesion

Targeting the tumor biophysical microenvironment to reduce resistance to immunotherapy

Immunotherapy based on immune checkpoint inhibitors has evolved into a new pillar of cancer treatment in clinics, but dealing with treatment resistance (either primary or acquired) is a major challenge. The tumor microenvironment (TME) has a substantial impact on the pathological behaviors and treatment response of many cancers. The biophysical clues in TME have recently been considered as important characteristics of cancer. Furthermore, there is mounting evidence that biophysical cues in TME play important roles in each step of the cascade of cancer immunotherapy that synergistically contribute to immunotherapy resistance. In this review, we summarize five main biophysical cues in TME that affect resistance to immunotherapy: extracellular matrix (ECM) structure, ECM stiffness, tumor interstitial fluid pressure (IFP), solid stress, and vascular shear stress. First, the biophysical factors involved in anti-tumor immunity and therapeutic antibody delivery processes are reviewed. Then, the causes of these five biophysical cues and how they contribute to immunotherapy resistance are discussed. Finally, the latest treatment strategies that aim to improve immunotherapy efficacy by targeting these biophysical cues are shared. This review highlights the biophysical cues that lead to immunotherapy resistance, also supplements their importance in related technologies for studying TME biophysical cues in vitro and therapeutic strategies targeting biophysical cues to improve the effects of immunotherapy.

Glycan structures and their recognition roles in the human blood group ABH/Ii, Lea, b, x, y and Sialyl Lea,x active cyst glycoproteins

Human ovarian cyst glycoproteins (HOC, cyst gps) isolated from pseudomucinous type of human ovarian cyst fluids is one of the richest and pioneer sources for studying biosynthesis, structures and functional roles of blood group ABH, Le^a,b,x,y, sLe^a and sLe^x active glycoproteins. After 70⁺ years of exploration, four top highlights are shared. (i) an updated concept of glycotopes and their internal structures in cyst gps was composited; (ii) the unknown codes of new genes in secreted cyst gps were unlocked as Le^x and Le^y; (iii) recognition profiles of cyst glycans and a sialic acid-rich (18%) glycan with lectins and antibodies were shown. (iv) Co-expression of Blood Group A/ A-Le^b/y and B/B-Le^b/y active Glycotopes in the same glycan chains were isolated and illustrated. These are the most advanced achievements since 1980.

Selectins and Immune Cells in Acute Myocardial Infarction and Post-infarction Ventricular Remodeling: Pathophysiology and Novel Treatments

The glycosciences aim to understand the impact of extracellular and intracellular carbohydrate structures on biological function. These glycans primarily fall into three major groups: lipid-linked carbohydrates that are referred to as glycosphingolipids or simply glycolipids; relatively short carbohydrate chains that are often O- or N-linked to proteins yielding common glycoproteins; and extended linear polymeric carbohydrate structures that are referred to as glycosaminoglycans (GAGs). Whereas, the impact of such carbohydrate structures has been extensively examined in cancer biology, their role in acute and chronic heart disease is less studied. In this context, a growing body of evidence indicates that glycans play an important role in immune mediated cell recruitment to damaged heart tissue to initiate wound healing and repair after injury. This is particularly important following ischemia and reperfusion that occurs in the heart in the setting of acute myocardial infarction. Here, immune system-mediated repair of the damaged myocardium plays a critical role in determining post-infarction ventricular remodeling, cardiac function, and patient outcome. Further, alterations in immune cell activity can promote the development of heart failure. The present review summarizes our current understanding of the phases of immune-mediated repair following myocardial infarction. It discusses what is known regarding glycans in mediating the recruitment of circulating immune cells during the early inflammatory stage of post-infarction repair, with focus on the selectin family of adhesion molecules. It offers future directions for research aimed at utilizing our knowledge of mechanisms underlying immune cell recruitment to either modulate leukocyte recruitment to the injured tissue or enhance the targeted delivery of biologic therapeutics such as stem cells in an attempt to promote repair of the damaged heart.

From Cancer Immunoediting to New Strategies in Cancer Immunotherapy: The Roles of Immune Cells and Mechanics in Oncology

For the last three decades, the concept of immunoediting has evolved to characterize our increasing understanding of the interactions between cells from the immune system and cancer development. Elucidating the role of immune cells in the progression of cancer has been very challenging due to their dual role; the immune system can either suppress tumor formation by killing cancer cells, or it can also promote tumor growth. Revealing how immune cells are hampered by the tumor microenvironment and how they aid tumor progression has signaled strategies to reverse these effects and control cancer cell growth; this has been the advent of immunotherapy design. More recently, the role of physical forces in the process of immunoediting has been highlighted by multiple studies focusing on understanding how force changes in the stiffness of the extracellular matrix and fluid flow shear stress contribute to tumor development. Using models in vitro that incorporate biomechanical components, it has been shown that these physical aspects are not only important during the formation and growth of primary tumors, but in the metastatic process as well. In this way, we have also gained insight into the interactions occurring within the vascular system, which are highly affected by the dynamics of physical collisions between cells and by shear forces. Here, we review the concept of cancer immunoediting with an emphasis on biomechanics and conclude with a summary on current immunotherapies and potential new strategies.

Lipid rafts enhance the binding constant of membrane-anchored receptors and ligands

Gaining insights into the binding of membrane-anchored receptors and ligands that mediate cell adhesion and signal transduction is of great significance for understanding numerous physiological processes driven by intercellular communication. Lipid rafts, microdomains in cell membranes enriched in cholesterol and saturated lipids such as sphingomyelin, are believed to serve as the essential platforms to recruit protein molecules for biological functions. An important question remains how the lipid rafts affect the binding constant of membrane-anchored receptors and ligands. We have investigated the adhesion of multicomponent membranes by using Monte Carlo simulations of a mesoscopic model with biologically relevant parameters. We find that the preferential partitioning of membrane-anchored receptor and ligand proteins in the lipid rafts significantly increases the binding constant of those proteins, in cooperation with the shape fluctuations of the membranes caused by thermal excitations. The binding constant can even be greater than that of the same receptors and ligands anchored to two apposing supported, planar membranes without shape fluctuations. The membrane shape fluctuations facilitate the binding of the anchored receptors and ligands, in contrast to the case of homogeneous membranes. Our results suggest that cells might regulate the binding of membrane-anchored receptor and ligand proteins by modulating the properties of lipid rafts such as area fraction, size and the affinity of rafts to the proteins.

Synthesis of a series of novel heteroglycoclusters and homoglycoclusters and the study of their anti-adhesion activities

A new series of mixed-type heteroglycoclusters containing mannose and lactose were synthesized. In the synthesis of rigid scaffold of heteroglycocluster, we found that trans-isomer could be prepared stereoselectively by means of Grubbs olefin cross-metathesis reactions. Moreover, sequential acylation using cyclic anhydride as scaffold could give cis-isomer. These two methods may provide complementarity of stereochemistry in heteroglycocluster assembling. The anti-adhesion activities of these compounds were assessed by Surface Plasmon Resonance (SPR) and static state cell-based adhesion assay. These results indicated that the rigid scaffold might not affect the anti-adhesion activities.

A computational framework for the automated construction of glycosylation reaction networks

Glycosylation is among the most common and complex post-translational modifications identified to date. It proceeds through the catalytic action of multiple enzyme families that include the glycosyltransferases that add monosaccharides to growing glycans, and glycosidases which remove sugar residues to trim glycans. The expression level and specificity of these enzymes, in part, regulate the glycan distribution or glycome of specific cell/tissue systems. Currently, there is no systematic method to describe the enzymes and cellular reaction networks that catalyze glycosylation. To address this limitation, we present a streamlined machine-readable definition for the glycosylating enzymes and additional methodologies to construct and analyze glycosylation reaction networks. In this computational framework, the enzyme class is systematically designed to store detailed specificity data such as enzymatic functional group, linkage and substrate specificity. The new classes and their associated functions enable both single-reaction inference and automated full network reconstruction, when given a list of reactants and/or products along with the enzymes present in the system. In addition, graph theory is used to support functions that map the connectivity between two or more species in a network, and that generate subset models to identify rate-limiting steps regulating glycan biosynthesis. Finally, this framework allows the synthesis of biochemical reaction networks using mass spectrometry (MS) data. The features described above are illustrated using three case studies that examine: i) O-linked glycan biosynthesis during the construction of functional selectin-ligands; ii) automated N-linked glycosylation pathway construction; and iii) the handling and analysis of glycomics based MS data. Overall, the new computational framework enables automated glycosylation network model construction and analysis by integrating knowledge of glycan structure and enzyme biochemistry. All the implemented features are provided as part of the Glycosylation Network Analysis Toolbox (GNAT), an open-source, platform-independent, MATLAB based toolbox for studies of Systems Glycobiology.

Distinct glycosyltransferases synthesize E-selectin ligands in human vs. mouse leukocytes

The binding of selectins to carbohydrate epitopes expressed on leukocytes is the first step in a multi-step cell adhesion cascade that controls the rate of leukocyte recruitment at sites of inflammation. The glycans that function as selectin-ligands are post-translationally synthesized by the serial action of Golgi resident enzymes called glycosyltransferases (glycoTs). Whereas much of our current knowledge regarding the role of glycoTs in constructing selectin-ligands comes from reconstituted biochemical investigations or murine models, tools to assess the impact of these enzymes on the human ligands are relatively underdeveloped. This is significant since the selectin-ligands, particularly those that bind E-selectin, vary between different leukocyte cell populations and they are also different in humans compared with mice. To address this shortcoming, a recent study by Buffone et al. (2013) outlines a systematic strategy to knockdown upto three glycoTs simultaneously in human leukocytes. The results suggest that the fucosyltransferases (FUTs) regulating selectin-ligand synthesis may be species-specific. In particular, they demonstrate that FUT9 plays a significant role during human, but not mouse, leukocyte-endothelial interactions. Overall, this article discusses the relative roles of the FUTs during human L-, E-, and P-selectin-ligand biosynthesis, and the potential that the knockdown strategy outlined here may assess the role of other glycoTs in human leukocytes also.

Systems glycobiology: biochemical reaction networks regulating glycan structure and function

There is a growing use of bioinformatics based methods in the field of Glycobiology. These have been used largely to curate glycan structures, organize array-based experimental data and display existing knowledge of glycosylation-related pathways in silico. Although the cataloging of vast amounts of data is beneficial, it is often a challenge to gain meaningful mechanistic insight from this exercise alone. The development of specific analysis tools to query the database is necessary. If these queries can integrate existing knowledge of glycobiology, new insights may be gained. Such queries that couple biochemical knowledge and mathematics have been developed in the field of Systems Biology. The current review summarizes the current state of the art in the application of computational modeling in the field of Glycobiology. It provides (i) an overview of experimental and online resources that can be used to construct glycosylation reaction networks, (ii) mathematical methods to formulate the problem including a description of ordinary differential equation and logic-based reaction networks, (iii) optimization techniques that can be applied to fit experimental data for the purpose of model reconstruction and for evaluating unknown model parameters, (iv) post-simulation analysis methods that yield experimentally testable hypotheses and (v) a summary of available software tools that can be used by non-specialists to perform many of the above functions.

Detection of site-specific glycosylation in proteins using flow cytometry

We tested the possibility that we may express unique peptide probes on cell surfaces, and detect site-specific glycosylation on these peptides using flow cytometry. Such development can enhance the application of flow cytometry to detect and quantify post-translational modifications in proteins. To this end, the N-terminal section of the human leukocyte glycoprotein PSGL-1 (P-selectin glycoprotein ligand-1) was modified to contain a poly-histidine tag followed by a proteolytic cleavage site. Amino acids preceding the cleavage site have a single O-linked glycosylation site. The recombinant protein called PSGL-1 (HT) was expressed on the surface of two mammalian cell lines, CHO and HL-60, using a lentiviral delivery approach. Results demonstrate that the N-terminal portion of PSGL-1 (HT) can be released from these cells by protease, and the resulting peptide can be readily captured and detected using cytometry-bead assays. Using this strategy, the peptide was immunoprecipitated onto beads bearing mAbs against either the poly-histidine sequence or the human PSGL-1. The carbohydrate epitope associated with the released peptide was detected using HECA-452 and CSLEX-1, monoclonal antibodies that recognize the sialyl Lewis-X epitope. Finally, the peptide released from cells could be separated and enriched using nickel chelate beads. Overall, such an approach that combines recombinant protein expression with flow cytometry may be useful to quantify changes in site-specific glycosylation for basic science and clinical applications.

Fluorinated per-acetylated GalNAc metabolically alters glycan structures on leukocyte PSGL-1 and reduces cell binding to selectins

Novel strategies to control the binding of adhesion molecules belonging to the selectin family are required for the treatment of inflammatory diseases. We tested the possibility that synthetic monosaccharide analogs can compete with naturally occurring sugars to alter the O-glycan content on human leukocyte cell surface selectin-ligand, P-selectin glycoprotein ligand-1 (PSGL-1). Resulting reduction in the sialyl Lewis-X-bearing epitopes on this ligand may reduce cell adhesion. Consistent with this hypothesis, 50muM per-acetylated 4F-GalNAc added to the growth media of promyelocytic HL-60 cells reduced the expression of the cutaneous lymphocyte associated-antigen (HECA-452 epitope) by 82% within 2 cell doubling cycles. Cell binding to all 3 selectins (L-, E-, and P-selectin) was reduced in vitro. 4F-GalNAc was metabolically incorporated into PSGL-1, and this was accompanied by an approximately 20% reduction in PSGL-1 glycan content. A 70% to 85% reduction in HECA-452 binding epitope and N-acetyl lactosamine content in PSGL-1 was also noted on 4F-GalNAc addition. Intravenous 4F-GalNAc infusion reduced leukocyte migration to the peritoneum in a murine model of thioglycolate-induced peritonitis. Thus, the compound has pharmacologic activity. Overall, the data suggest that 4F-GalNAc may be applied as a metabolic inhibitor to reduce O-linked glycosylation, sialyl Lewis-X formation, and leukocyte adhesion via the selectins.

Expression of sialyl Lex, sialyl Lea, Lex and Ley glycotopes in secreted human ovarian cyst glycoproteins

Human blood group A, B, H, Ii, Le(a) and Le(b) antigens and their determinants expressed on ovarian cyst glycoproteins have been studied for over five decades. However, little is known about sialyl Le(x) and sialyl Le(a) glycotopes, which play essential roles in normal immunity, inflammation, and cancer cell metastasis. Furthermore, Le(x) and Le(y) were classified as glycotopes of unknown genes. Identification of these Lewis epitopes was hampered by the lack of specific antibodies. In this study, the occurrence of sialyl Le(x), sialyl Le(a), Le(x) and Le(y) reactivities in cyst glycoproteins was characterized by enzyme-linked immunosorbent assays. The results indicated that most human ovarian cyst glycoproteins carried Le(x) (8/25) and/or Le(y) (17/25) glycotopes. The expression (epitopes) of the new genes described in previous reports are Le(x) and Le(y) glycotopes; the reactivities of sialyl Le(x) and sialyl Le(a) glycotopes in secreted cyst glycoproteins may be affected by the conditions of purification; the relationship between Le(y) and human blood group ABH was confirmed; recognition profiles of sialyl Le(x), sialyl Le(a), Le(x) and Le(y) present in the carbohydrate chains of water-soluble cyst glycoproteins were illustrated; possible attachments of glycotopes to the internal carbohydrate complex of cyst glycoproteins have been reconstructed; proposed biosynthetic pathways for the formation of sialyl Le(a), sialyl Le(x), Le(x), Le(y), ALe(y) and BLe(y) determinant structures on Type I and Type II core structures of human ovarian cyst glycoproteins are also included in this study.

Systems-level modeling of cellular glycosylation reaction networks: O-linked glycan formation on natural selectin ligands

MOTIVATION

The emerging field of Glycomics requires the development of systems-based modeling strategies to relate glycosyltransferase gene expression and enzyme activity with carbohydrate structure and function.

RESULTS

We describe the application of object oriented programming concepts to define glycans, enzymes, reactions, pathways and compartments for modeling cellular glycosylation reaction networks. These class definitions are combined with current biochemical knowledge to define potential reaction networks that participate in the formation of the sialyl Lewis-X (sLe(X)) epitope on O-glycans linked to a leukocyte cell-surface glycoprotein, P-selectin Glycoprotein Ligand-1 (PSGL-1). Subset modeling, hierarchical clustering, principal component analysis and adjoint sensitivity analysis are applied to refine the reaction network and to quantify individual glycosyltransferase rate constants. Wet-lab experiments validate estimates from computer modeling. Such analysis predicts that sLe(X) expression varies directly with sialyltransferase alpha2,3ST3Gal-IV expression and inversely with alpha2,3ST3Gal-I/II.

AVAILABILITY

SBML files for all converged models are available at http://www.eng.buffalo.edu/~neel/bio_reaction_network.html

Systems-level studies of glycosyltransferase gene expression and enzyme activity that are associated with the selectin binding function of human leukocytes

The application of systems biology methods in the emerging field of glycomics requires the collection and integration of glycosyltransferase data at the gene and enzyme level for the purpose of hypothesis generation. We systematically examined the relationship between gene expression, glycosyltransferase activity, glycan expression, and selectin-binding function in different systems, including human neutrophils, undifferentiated HL-60 (human promyelocytic cells), differentiated HL-60, and HL-60 synchronized in specific growth phases. Results demonstrate that 1) the sLe(X) (sialyl-Lewis-X) epitope is expressed in P-selectin glycoprotein ligand-1 (PSGL-1) from neutrophils at higher levels compared with HL-60. This variation may be due to differences in the relative activities of alpha1,3-fucosyltransferases and alpha2,3-sialyltransferases in these two cell types. 2) HL-60 cell differentiation along granulocyte lineage increased the activity of beta1,4GalT and beta1,3GlcNAcT by 1.6- to 3.2-fold. This may contribute to LacNAc chain extension as evidenced by the 1.7-fold increase in DSA-lectin (lectin recognizing LacNAc) binding to cells after differentiation. 3) The activity of enzymes contributing to sLe(X) formation in leukocytes likely varies as ST3[Galbeta1,4GlcNAc] < or = alpha1,3FT[sialyl-LacNAc] < beta1,3GlcNAcT. 4) O-glycan specific glycosyltransferase activity does not undergo periodic variation with cell cycle phases. Overall, gene expression and enzyme activity data combined with knowledge of biochemistry can predict the resulting glycan structures and yield viable experimentally testable hypothesis.

Lectin-like domain of thrombomodulin binds to its specific ligand Lewis Y antigen and neutralizes lipopolysaccharide-induced inflammatory response

Thrombomodulin (TM), a widely expressing glycoprotein originally identified in vascular endothelium, is an important cofactor in the protein C anticoagulant system. TM appears to exhibit anti-inflammatory ability through both protein C-dependent and -independent pathways. We presently have demonstrated that recombinant N-terminal lectinlike domain of TM (rTMD1) functions as a protective agent against sepsis caused by Gram-negative bacterial infections. rTMD1 caused agglutination of Escherichia coli and Klebsiella pneumoniae and enhanced the macrophage phagocytosis of these Gram-negative bacteria. Moreover, rTMD1 bound to the Klebsiella pneumoniae and lipopolysaccharide (LPS) by specifically interacting with Lewis Y antigen. rTMD1 inhibited LPS-induced inflammatory mediator production via interference with CD14 and LPS binding. Furthermore, rTMD1 modulated LPS-induced mitogen-activated protein kinase and nuclear factor-kappaB signaling pathway activations and inducible nitric oxide synthase expression in macrophages. Administration of rTMD1 protected the host by suppressing inflammatory responses induced by LPS and Gram-negative bacteria, and enhanced LPS and bacterial clearance in sepsis. Thus, rTMD1 can be used to defend against bacterial infection and inhibit LPS-induced inflammatory responses, suggesting that rTMD1 may be valuable in the treatment of severe inflammation in sepsis, especially in Gram-negative bacterial infections.

Differential regulation of neutrophil CD18 integrin function by di- and tri-valent cations: manganese vs. gadolinium

Affinity regulation of integrin function plays an important role during both leukocyte-endothelial and leukocyte-leukocyte interactions. We compared the roles of Mn(2+) (Manganese) and Gd(3+) (Gadolinium) in regulating leukocyte CD18-integrin function. We observed that: (i) Both cations prolonged neutrophil homotypic aggregation following chemoattractant IL-8 stimulation, with Gd(3+) being effective at doses two orders of magnitude (10 microM range) lower that Mn(2+). (ii) While both Gd(3+) and Mn(2+) mediate homotypic cell aggregation via L: -selectin and CD18 integrins, their effects on the integrin subunits, LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18), was different. Gd(3+) altered both LFA-1 and Mac-1 function, while the dominant effect of Mn(2+) was on Mac-1. This effect of Gd(3+) on LFA-1 function was confirmed in cell-free studies that measured the binding of recombinant ICAM-1 to LFA-1 immobilized on beads. (iii) Both ions augmented the binding of 327C, an antibody that recognizes active CD18 on human neutrophils, both in the presence and absence of exogenous IL-8. The effects of Mn(2+) was more pronounced since it caused 3-4-fold increase in mAb 327C binding to neutrophils compared to Gd(3+) which increased antibody binding by only approximately 80%. 327C binding was partially reduced by Ca(2+). Further, 327C binding induced by Mn(2+) did not correlate tightly with cell adhesion function. (iv) In studies that monitored intracellular Ca(2+) ([Ca(2+)](i)), the addition of Mn(2+) but not Gd(3+) to neutrophils altered [Ca(2+)](i) levels. Overall, while both Gd(3+) and Mn(2+) stabilize high affinity CD18 mediated cell adhesion, Gd(3+) affects integrin conformation while Mn(2+) may also trigger other effects.

Biomechanics of P-selectin PSGL-1 bonds: shear threshold and integrin-independent cell adhesion

Platelet-leukocyte adhesion may contribute to thrombosis and inflammation. We examined the heterotypic interaction between unactivated neutrophils and either thrombin receptor activating peptide (TRAP)-stimulated platelets or P-selectin-bearing beads (Ps-beads) in suspension. Cone-plate viscometers were used to apply controlled shear rates from 14 to 3000/s. Platelet-neutrophil and bead-neutrophil adhesion analysis was performed using both flow cytometry and high-speed videomicroscopy. We observed that although blocking antibodies against either P-selectin or P-selectin glycoprotein ligand-1 (PSGL-1) alone inhibited platelet-neutrophil adhesion by approximately 60% at 140/s, these reagents completely blocked adhesion at 3000/s. Anti-Mac-1 alone did not alter platelet-neutrophil adhesion rates at any shear rate, though in synergy with selectin antagonists it abrogated cell binding. Unstimulated neutrophils avidly bound Ps-beads and activated platelets in an integrin-independent manner, suggesting that purely selectin-dependent cell adhesion is possible. In support of this, antagonists against P-selectin or PSGL-1 caused dissociation of previously formed platelet-neutrophil and Ps-bead neutrophil aggregates under shear in a variety of experimental systems, including in assays performed with whole blood. In studies where medium viscosity and shear rate were varied, a shear threshold for P-selectin PSGL-1 binding was also noted at shear rates <100/s when Ps-beads collided with isolated neutrophils. Results are discussed in light of biophysical computations that characterize the collision between unequal-size particles in linear shear flow. Overall, our studies reveal an integrin-independent regime for cell adhesion and weak shear threshold for P-selectin PSGL-1 interactions that may be physiologically relevant.

Affinity and kinetics of sialyl Lewis-X and core-2 based oligosaccharides binding to L- and P-selectin

Soluble oligosaccharide mimetics of natural selectin ligands act as competitive inhibitors of leukocyte adhesion in models of inflammation. We quantified the binding of simple oligosaccharides based on sialyl Lewis-X (sLe(X)) and complex molecules with the core-2 structure to L- and P-selectin, under both static and fluid flow conditions. Isolated human neutrophils were employed to mimic the physiological valency of selectins and selectin ligands. Surface plasmon resonance studies quantified binding kinetics. We observed the following: (i) The functional group at the anomeric position of carbohydrates plays an important role during selectin recognition, since sLe(X) and sialyl Lewis-a (sLe(a)) were approximately 5-7-fold poorer inhibitors of L-selectin mediated cell adhesion compared to their methyl glycosides. (ii) Despite their homology to physiological glycans, the putative carbohydrate epitopes of GlyCAM-1 and PSGL-1 bound selectins with low affinity comparable to that of sLe(X)-selectin interactions. Thus, besides the carbohydrate portion, the protein core of GlyCAM-1 or the presentation of carbohydrates in clusters on this glycoprotein may contribute to selectin recognition. (iii) A compound Galbeta1,4(Fucalpha1,3)GlcNAcbeta1,6(GalNAcbeta1,3)GalNAcalpha-OMe was identified which blocked L- and P-selectin binding at 30-100-fold lower doses than sLe(X). (iv) Surface plasmon resonance experiments determined that an sLe(X) analogue (TBC1269) competitively inhibited, via steric/allosteric mechanisms, the binding of two anti-P-selectin function blocking antibodies that recognized different epitopes of P-selectin. (v) TBC1269 bound P-selectin via both calcium-dependent and -independent mechanisms, with K(D) of approximately 111.4 microM. The measured on- and off-rates were high (k(off) > 3 s(-)(1), k(on) > 27,000 M(-)(1) s(-)(1)). Similar binding kinetics are expected for sLe(X)-selectin interactions. Taken together, our study provides new insight into the kinetics and mechanisms of carbohydrate interaction with selectins.

Survey of the year 2004 commercial optical biosensor literature

The year 2004 represents a milestone for the biosensor research community: in this year, over 1000 articles were published describing experiments performed using commercially available systems. The 1038 papers we found represent an approximately 10% increase over the past year and demonstrate that the implementation of biosensors continues to expand at a healthy pace. We evaluated the data presented in each paper and compiled a 'top 10' list. These 10 articles, which we recommend every biosensor user reads, describe well-performed kinetic, equilibrium and qualitative/screening studies, provide comparisons between binding parameters obtained from different biosensor users, as well as from biosensor- and solution-based interaction analyses, and summarize the cutting-edge applications of the technology. We also re-iterate some of the experimental pitfalls that lead to sub-optimal data and over-interpreted results. We are hopeful that the biosensor community, by applying the hints we outline, will obtain data on a par with that presented in the 10 spotlighted articles. This will ensure that the scientific community at large can be confident in the data we report from optical biosensors.