Efficient production of fluorophore-labeled CC chemokines for biophysical studies using recombinant enterokinase and recombinant sortase

Chemokines are important immune system proteins, many of which mediate inflammation due to their function to activate and cause chemotaxis of leukocytes. An important anti-inflammatory strategy is therefore to bind and inhibit chemokines, which leads to the need for biophysical studies of chemokines as they bind various possible partners. Because a successful anti-chemokine drug should bind at low concentrations, techniques such as fluorescence anisotropy that can provide nanomolar signal detection are required. To allow fluorescence experiments to be carried out on chemokines, a method is described for the production of fluorescently labeled chemokines. First, a fusion-tagged chemokine is produced in Escherichia coli, then efficient cleavage of the N-terminal fusion partner is carried out with lab-produced enterokinase, followed by covalent modification with a fluorophore, mediated by the lab-produced sortase enzyme. This overall process reduces the need for expensive commercial enzymatic reagents. Finally, we utilize the product, vMIP-fluor, in binding studies with the chemokine binding protein vCCI, which has great potential as an anti-inflammatory therapeutic, showing a binding constant for vCCI:vMIP-fluor of 0.37 ± 0.006 nM. We also show how a single modified chemokine homolog (vMIP-fluor) can be used in competition assays with other chemokines and we report a Kd for vCCI:CCL17 of 14 μM. This work demonstrates an efficient method of production and fluorescent labeling of chemokines for study across a broad range of concentrations.

Pyroglutamination-Induced Changes in the Physicochemical Features of a CXCR4 Chemokine Peptide: Kinetic and Structural Analysis

We investigate the physicochemical effects of pyroglutamination on the QHALTSV-NH2 peptide, a segment of cytosolic helix 8 of the human C-X-C chemokine G-protein-coupled receptor type 4 (CXCR4). This modification, resulting from the spontaneous conversion of glutamine to pyroglutamic acid, has significant impacts on the physicochemical features of peptides. Using a static approach, we compared the transformation in different conditions and experimentally found that the rate of product formation increases with temperature, underscoring the need for caution during laboratory experiments to prevent glutamine cyclization. Circular dichroism experiments revealed that the QHALTSV-NH2 segment plays a minor role in the structuration of H8 CXCR4; however, its pyroglutaminated analogue interacts differently with its chemical environment, showing increased susceptibility to solvent variations compared to the native form. The pyroglutaminated analogue exhibits altered behavior when interacting with lipid models, suggesting a significant impact on its interaction with cell membranes. A unique combination of atomic force microscopy and infrared nanospectroscopy revealed that pyroglutamination affects supramolecular self-assembly, leading to highly packed molecular arrangements and a crystalline structure. Moreover, the presence of pyroglumatic acid has been found to favor the formation of amyloidogenic aggregates. Our findings emphasize the importance of considering pyroglutamination in peptide synthesis and proteomics and its potential significance in amyloidosis.

Ligand-binding and -scavenging of the chemerin receptor GPR1

Tight regulation of cytokines is essential for the initiation and resolution of inflammation. Chemerin, a mediator of innate immunity, mainly acts on chemokine-like receptor 1 (CMKLR1) to induce the migration of macrophages and dendritic cells. The role of the second chemerin receptor, G protein-coupled receptor 1 (GPR1), is still unclear. Here we demonstrate that GPR1 shows ligand-induced arrestin3 recruitment and internalization. The chemerin C-terminus triggers this activation by folding into a loop structure, binding to aromatic residues in the extracellular loops of GPR1. While this overall binding mode is shared between GPR1 and CMKLR1, differences in their respective extracellular loop 2 allowed for the design of the first GPR1-selective peptide. However, our results suggest that ligand-induced arrestin recruitment is not the only mode of action of GPR1. This receptor also displays constitutive internalization, which allows GPR1 to internalize inactive peptides efficiently by an activation-independent pathway. Our results demonstrate that GPR1 takes a dual role in regulating chemerin activity: as a signaling receptor for arrestin-based signaling on one hand, and as a scavenging receptor with broader ligand specificity on the other.

The multilayered complexity of the chemokine receptor system

The chemokines receptor family are membrane-expressed class A-specific seven-transmembrane receptors linked to G proteins. Through interaction with the corresponding ligands, the chemokines, they induce a wide variety of cellular responses including cell polarization, movement, immune and inflammatory responses, as well as the prevention of HIV-1 infection. Like a Russian matryoshka doll, the chemokine receptor system is more complex than initially envisaged. This review focuses on the mechanisms that contribute to this dazzling complexity and how they modulate the signaling events triggered by chemokines. The chemokines and their receptors exist as monomers, dimers and oligomers, their expression pattern is highly regulated, and the ligands can bind distinct receptors with similar affinities. The use of novel imaging-based technologies, particularly real-time imaging modalities, has shed new light on the very dynamic conformations that chemokine receptors adopt depending on the cellular context, and that affect chemokine-mediated responses. This complex scenario presents both challenging and exciting opportunities for drug discovery.

Chemokines and Bone

Chemokines are a family of small proteins, subdivided by their conserved cysteine residues and common structural features. Chemokines interact with their cognate G-protein-coupled receptors to elicit downstream signals that result in cell migration, proliferation, and survival. This review presents evidence for how the various CXC and CC subfamily chemokines influence bone hemostasis by acting on osteoclasts, osteoblasts, and progenitor cells. Also discussed are the ways in which chemokines contribute to bone loss as a result of inflammatory diseases such as rheumatoid arthritis, HIV infection, and periodontal infection. Both positive and negative effects of chemokines on bone formation and bone loss are presented. In addition, the role of chemokines in altering the bone microenvironment through effects on angiogenesis and tumor invasion is discussed. Very few therapeutic agents that influence bone formation by targeting chemokines or chemokine receptors are available, although a few are currently being evaluated.

Glycosaminoglycan Interactions Fine-Tune Chemokine-Mediated Neutrophil Trafficking: Structural Insights and Molecular Mechanisms

Circulating neutrophils, rapidly recruited in response to microbial infection, form the first line in host defense. Humans express ~50 chemokines, of which a subset of seven chemokines, characterized by the conserved "Glu-Leu-Arg" motif, mediate neutrophil recruitment. Neutrophil-activating chemokines (NACs) share similar structures, exist as monomers and dimers, activate the CXCR2 receptor on neutrophils, and interact with tissue glycosaminoglycans (GAGs). Considering cellular assays have shown that NACs have similar CXCR2 activity, the question has been and remains, why do humans express so many NACs? In this review, we make the case that NACs are not redundant and that distinct GAG interactions determine chemokine-specific in vivo functions. Structural studies have shown that the GAG-binding interactions of NACs are distinctly different, and that conserved and specific residues in the context of structure determine geometries that could not have been predicted from sequences alone. Animal studies indicate recruitment profiles of monomers and dimers are distinctly different, monomer-dimer equilibrium regulates recruitment, and that recruitment profiles vary between chemokines and between tissues, providing evidence that GAG interactions orchestrate neutrophil recruitment. We propose in vivo GAG interactions impact several chemokine properties including gradients and lifetime, and that these interactions fine-tune and define the functional response of each chemokine that can vary between different cell and tissue types for successful resolution of inflammation.

Prochemerin cleavage by factor XIa links coagulation and inflammation

Chemerin is a chemoattractant and adipokine that circulates in blood as inactive prochemerin (chem163S). Chem163S is activated by a series of C-terminal proteolytic cleavages resulting in diverse chemerin forms with different levels of activity. We screened a panel of proteases in the coagulation, fibrinolytic, and inflammatory cascades to identify those that process prochemerin in plasma. Factor XIa (FXIa) cleaved chem163S, generating a novel chemerin form, chem162R, as an intermediate product, and chem158K, as the final product. Processing at Arg162 was not required for cleavage at Lys158 or regulation of chemerin bioactivity. Contact phase activation of human platelet-poor plasma by kaolin led to cleavage of chem163S, which was undetectable in FXI-depleted plasma and markedly enhanced in platelet-rich plasma (PRP). Contact phase activation by polyphosphate in PRP resulted in 75% cleavage of chem163S. This cleavage was partially inhibited by hirudin, which blocks thrombin activation of FXI. After activation of plasma, levels of the most potent form of chemerin, chem157S, as well as inactive chem155A, increased. Plasma levels of chem163S in FXI-deficient patients were significantly higher compared with a matched control group (91 ± 10 ng/mL vs 58 ± 3 ng/mL, n = 8; P < .01) and inversely correlated with the plasma FXI levels. Thus FXIa, generated on contact phase activation, cleaves chem163S to generate chem158K, which can be further processed to the most active chemerin form, providing a molecular link between coagulation and inflammation.

Chemokines from a Structural Perspective

Chemokines are a family of small, highly conserved cytokines that mediate various biological processes, including chemotaxis, hematopoiesis, and angiogenesis, and that function by interacting with cell surface G-Protein Coupled Receptors (GPCRs). Because of their significant involvement in various biological functions and pathologies, chemokines and their receptors have been the focus of therapeutic discovery for clinical intervention. There are several sub-families of chemokines (e.g., CXC, CC, C, and CX3C) defined by the positions of sequentially conserved cysteine residues. Even though all chemokines also have a highly conserved, three-stranded β-sheet/α-helix tertiary structural fold, their quarternary structures vary significantly with their sub-family. Moreover, their conserved tertiary structures allow for subunit swapping within and between sub-family members, thus promoting the concept of a “chemokine interactome”. This review is focused on structural aspects of CXC and CC chemokines, their functional synergy and ability to form heterodimers within the chemokine interactome, and some recent developments in structure-based chemokine-targeted drug discovery.

What Do Structures Tell Us About Chemokine Receptor Function and Antagonism?

Chemokines and their cell surface G protein-coupled receptors are critical for cell migration, not only in many fundamental biological processes but also in inflammatory diseases and cancer. Recent X-ray structures of two chemokines complexed with full-length receptors provided unprecedented insight into the atomic details of chemokine recognition and receptor activation, and computational modeling informed by new experiments leverages these insights to gain understanding of many more receptor:chemokine pairs. In parallel, chemokine receptor structures with small molecules reveal the complicated and diverse structural foundations of small molecule antagonism and allostery, highlight the inherent physicochemical challenges of receptor:chemokine interfaces, and suggest novel epitopes that can be exploited to overcome these challenges. The structures and models promote unique understanding of chemokine receptor biology, including the interpretation of two decades of experimental studies, and will undoubtedly assist future drug discovery endeavors.

Inflammatory 'double hit' model of temporomandibular joint disorder with elevated CCL2, CXCL9, CXCL10, RANTES and behavioural hypersensitivity in TNFR1/R2-/- mice

BACKGROUND

Patients with temporomandibular joint disorders (TMD), reactive arthritis and rheumatoid arthritis often have combined etiology of hereditary and microenvironmental factors contributing to joint pain. Multiple clinical and animal studies indicate 'double-hit' inflammatory insults can cause chronic inflammation. The first inflammatory insult primes the immune system and subsequent insults elicit amplified responses. The present 'double hit' study produced a chronic orofacial pain model in mice with genetic deletion of both TNFα receptors (TNFR1/R2-/-), investigating the main nociceptive signalling pathways in comparisons to wild type mice.

METHODS

An initial inflammatory insult was given unilaterally into the temporomandibular joint (TMJ). Secondary hypersensitivity was tested on the skin over the TMJ throughout the experiment. Three weeks later after complete reversal of hypersensitivity, a second inflammatory insult was imposed on the colon. Pharmacological interventions were tested for efficacy after week 10 when hypersensitivity was chronic in TNFR1/R2-/- mice. Serum cytokines were analysed at Days 1, 14, and Week 18.

RESULTS

The double hit insult produced chronic hypersensitivity continuing through the 4-month experimental timeline in the absence of TNFα signalling. P2X7 and NMDA receptor antagonists temporarily attenuated chronic hypersensitivity. Serum cytokine/chemokine analysis on Day 14 when CFA induced hypersensitivity was resolved identified increased levels of pro-inflammatory cytokines CCL2, CXCL9, CXCL10, RANTES and decreased levels of anti-inflammatory cytokines IL-1ra and IL-4 in TNFR1/R2-/- compared to WT mice.

CONCLUSIONS

These data suggest a causal feed-forward signalling cascade of these little studied cytokines have the potential to cause recrudescence in this orofacial inflammatory pain model in the absence of TNFα signalling.

SIGNIFICANCE

Using a mouse model of chronic inflammatory temporomandibular joint disorder, we determined that absence of functional TNFR1/R2 induces aberrant inflammatory signalling caused by other increased pro-inflammatory and decreased anti-inflammatory cytokines that could serve as blood biomarkers and may predict disease progression.

Mechanisms of Regulation of the Chemokine-Receptor Network

The interactions of chemokines with their G protein-coupled receptors promote the migration of leukocytes during normal immune function and as a key aspect of the inflammatory response to tissue injury or infection. This review summarizes the major cellular and biochemical mechanisms by which the interactions of chemokines with chemokine receptors are regulated, including: selective and competitive binding interactions; genetic polymorphisms; mRNA splice variation; variation of expression, degradation and localization; down-regulation by atypical (decoy) receptors; interactions with cell-surface glycosaminoglycans; post-translational modifications; oligomerization; alternative signaling responses; and binding to natural or pharmacological inhibitors.

CARD9 as a potential target in cardiovascular disease

Systemic inflammation and localized macrophage infiltration have been implicated in cardiovascular pathologies, including coronary artery disease, carotid atherosclerosis, heart failure, obesity-associated heart dysfunction, and cardiac fibrosis. Inflammation induces macrophage infiltration and activation and release of cytokines and chemokines, causing tissue dysfunction by instigating a positive feedback loop that further propagates inflammation. Cytosolic adaptor caspase recruitment domain family, member 9 (CARD9) is a protein expressed primarily by dendritic cells, neutrophils, and macrophages, in which it mediates cytokine secretion. The purpose of this review is to highlight the role of CARD9 as a potential target in inflammation-related cardiovascular pathologies.

Adipocyte-secreted chemerin is processed to a variety of isoforms and influences MMP3 and chemokine secretion through an NFkB-dependent mechanism

Obesity is associated with white adipose tissue (WAT) remodelling characterized by changes in cellular composition, size, and adipokine secretion. Levels of the adipokine chemerin are positively associated with obesity; however, the biological function of chemerin in WAT is poorly understood. We identified factors involved in WAT remodelling, including matrix metalloproteinase (Mmp)3 and chemokines (Ccl2, 3, 5, 7), as novel targets of chemerin signalling in mature adipocytes. Inhibition of chemerin signalling increased MMP activity and the recruitment of macrophages towards adipocyte-conditioned media. These effects were mediated through increases in NFkB signalling, suggesting that chemerin exerts an anti-inflammatory influence. We also demonstrate that multiple chemerin isoforms are present in adipocyte-conditioned media and that adipocyte-secreted chemerin, but not synthetic chemerin, recapitulates the activity of endogenous chemerin. Considered altogether, this suggests that endogenously secreted chemerin plays an autocrine/paracrine role in WAT, identifying chemerin as a therapeutic target to modulate adipose remodelling.

PET/CT Imaging of Chemokine Receptors in Inflammatory Atherosclerosis Using Targeted Nanoparticles

Atherosclerosis is inherently an inflammatory process that is strongly affected by the chemokine-chemokine receptor axes regulating the trafficking of inflammatory cells at all stages of the disease. Of the chemokine receptor family, some specifically upregulated on macrophages play a critical role in plaque development and may have the potential to track plaque progression. However, the diagnostic potential of these chemokine receptors has not been fully realized. On the basis of our previous work using a broad-spectrum peptide antagonist imaging 8 chemokine receptors together, the purpose of this study was to develop a targeted nanoparticle for sensitive and specific detection of these chemokine receptors in both a mouse vascular injury model and a spontaneously developed mouse atherosclerosis model.

METHODS

The viral macrophage inflammatory protein-II (vMIP-II) was conjugated to a biocompatible poly(methyl methacrylate)-core/polyethylene glycol-shell amphiphilic comblike nanoparticle through controlled conjugation and polymerization before radiolabeling with (64)Cu for PET imaging in an apolipoprotein E-deficient (ApoE(-/-)) mouse vascular injury model and a spontaneous ApoE(-/-) mouse atherosclerosis model. Histology, immunohistochemistry, and real-time reverse transcription polymerase chain reaction were performed to assess the plaque progression and upregulation of chemokine receptors.

RESULTS

The chemokine receptor-targeted (64)Cu-vMIP-II-comb showed extended blood retention and improved biodistribution. PET imaging showed specific tracer accumulation at plaques in ApoE(-/-) mice, confirmed by competitive receptor blocking studies and assessment in wild-type mice. Histopathologic characterization showed the progression of plaque including size and macrophage population, corresponding to the elevated concentration of chemokine receptors and more importantly increased PET signals.

CONCLUSION

This work provides a useful nanoplatform for sensitive and specific detection of chemokine receptors to assess plaque progression in mouse atherosclerosis models.

Structure-function relationships in thrombin-activatable fibrinolysis inhibitor

Thrombin-activatable fibrinolysis inhibitor (TAFI) is an important regulator in the balance of coagulation and fibrinolysis. TAFI is a metallocarboxypeptidase that circulates in plasma as zymogen. Activated TAFI (TAFIa) cleaves C-terminal lysine or arginine residues from peptide substrates. The removal of C-terminal lysine residues from partially degraded fibrin leads to reduced plasmin formation and thus attenuation of fibrinolysis. TAFI also plays a role in inflammatory processes via the removal of C-terminal arginine or lysine residues from bradykinin, thrombin-cleaved osteopontin, C3a, C5a and chemerin. TAFI has been studied extensively over the past three decades and recent publications provide a wealth of information, including crystal structures, mutants and structural data obtained with antibodies and peptides. In this review, we combined and compared available data on structure/function relationships of TAFI.

Tuberostemonine N, an active compound isolated from Stemona tuberosa, suppresses cigarette smoke-induced sub-acute lung inflammation in mice

OBJECTIVE

Our previous study demonstrated that a Stemona tuberosa extract had significant effects on cigarette smoking (CS)-induced lung inflammation in mice. The present study evaluated the potential of tuberostemonine N (T.N) to prevent airway inflammation and suppress airway responses in a CS-induced in vivo COPD model.

METHODS

T.N was isolated from the root of ST and analyzed using 1D and 2D NMR. The purity of T.N was accessed using HPLC-ELSD analysis. C57BL/6 mice in this study were whole-body exposed to mainstream CS or room air for 4 weeks, and T.N (1, 5 and 10 mg/kg body wt.) was administered to mice via intraperitoneal (i.p.) injection before CS exposure. The number of inflammatory cells, including neutrophils, macrophages and lymphocytes, and the amount of proinflammatory cytokines and chemokines were accessed from bronchoalveolar lavage fluid (BALF) to investigate the anti-inflammatory effects of T.N. Average alveoli size was also measured using histological analyses.

RESULTS

Cellular profiles and histopathological analyses revealed that the infiltration of peribronchial and perivascular inflammatory cells decreased significantly in the T.N-treated groups compared to the CS-exposed control group. T.N significantly inhibited the secretion of proinflammatory cytokines and chemokines in BALF and decreased alveoli size in lung tissue.

CONCLUSIONS

These data suggest that T.N exerts anti-inflammatory effects against airway inflammation, and T.N may be a novel therapeutic agent for lung diseases, such as COPD.

Metabolic profiling of ligands for the chemokine receptor CXCR3 by liquid chromatography-mass spectrometry coupled to bioaffinity assessment

Chemokine receptors belong to the class of G protein-coupled receptors and are important in the host defense against infections and inflammation. However, aberrant chemokine signaling is linked to different disorders such as cancer, central nervous system and immune disorders, and viral infections [Scholten DJ et al. (2012) Br J Pharmacol 165(6):1617–1643]. Modulating the chemokine receptor function provides new ways of targeting specific diseases. Therefore, discovery and development of drugs targeting chemokine receptors have received considerable attention from the pharmaceutical industry in the past decade. Along with that, the determination of bioactivities of individual metabolites derived from lead compounds towards chemokine receptors is crucial for drug selectivity, pharmacodynamics, and potential toxicity issues. Therefore, advanced analytical methodologies are in high demand. This study is aimed at the optimization of a new analytical method for metabolic profiling with parallel bioaffinity assessment of CXCR3 ligands of the azaquinazolinone and piperazinyl-piperidine class and their metabolites. The method is based on mass spectrometric (MS) identification after liquid chromatographic (LC) separation of metabolic mixtures. The bioaffinity assessment is performed “at-line” via high-resolution nanofractionation onto 96-well plates allowing direct integration of radioligand binding assays. This new method enables identification of metabolites from lead compounds with associated estimation of their individual bioaffinity. Moreover, the identification of the metabolite structures via accurate mass measurements and MS² allows the identification of liable metabolic “hotspots” for further lead optimization. The efficient combination of chemokine receptor ligand binding assays with analytical techniques, involving nanofractionation as linking technology, allows implementation of comprehensive metabolic profiling in an early phase of the drug discovery process.

Interference with glycosaminoglycan-chemokine interactions with a probe to alter leukocyte recruitment and inflammation in vivo

In vivo leukocyte recruitment is not fully understood and may result from interactions of chemokines with glycosaminoglycans/GAGs. We previously showed that chlorite-oxidized oxyamylose/COAM binds the neutrophil chemokine GCP-2/CXCL6. Here, mouse chemokine binding by COAM was studied systematically and binding affinities of chemokines to COAM versus GAGs were compared. COAM and heparan sulphate bound the mouse CXC chemokines KC/CXCL1, MIP-2/CXCL2, IP-10/CXCL10 and I-TAC/CXCL11 and the CC chemokine RANTES/CCL5 with affinities in the nanomolar range, whereas no binding interactions were observed for mouse MCP-1/CCL2, MIP-1α/CCL3 and MIP-1β/CCL4. The affinities of COAM-interacting chemokines were similar to or higher than those observed for heparan sulphate. Although COAM did not display chemotactic activity by itself, its co-administration with mouse GCP-2/CXCL6 and MIP-2/CXCL2 or its binding of endogenous chemokines resulted in fast and cooperative peritoneal neutrophil recruitment and in extravasation into the cremaster muscle invivo. These local GAG mimetic features by COAM within tissues superseded systemic effects and were sufficient and applicable to reduce LPS-induced liver-specific neutrophil recruitment and activation. COAM mimics glycosaminoglycans and is a nontoxic probe for the study of leukocyte recruitment and inflammation invivo.

High-resolution mass spectrometry and partial de novo sequencing constitute a useful approach for determining the profile of chemokine secretion following the stimulation of human intestinal epithelial cells

RATIONALE

Intestinal epithelial cells (IEC) secrete many chemokines in response to proinflammatory stimuli. We investigated their role in the mucosal inflammatory response in the intestine, by developing a non-targeted approach for analyzing the profile of peptides secreted by stimulated IEC, based on differential mass spectrometry analysis.

METHODS

Lipopolysaccharide (LPS) was incubated with IEC as a proinflammatory stimulus. Differential peptidomic analysis was then carried out, comparing the profiles of IEC with and without LPS stimulation. A mass spectrometry procedure was developed, based on a liquid chromatography/tandem mass spectrometry (LC/MS/MS) approach without enzymatic pretreatment of the peptides. Partial de novo sequencing was carried out by Fourier transform ion cyclotron resonance (FTICR), and the native peptides in the culture media were identified.

RESULTS

A major ion (m/z 7862.51) detected after stimulation was identified as GRO alpha and a minor ion (m/z 8918.17) was identified as IL-8. ELISA-based comparisons gave results consistent with those obtained by MS. Surprisingly, GRO alpha was secreted in amounts 5 to 15 times higher than those for IL-8 in our cellular model. The truncated form of IL-8, resulting from activation, was detected and distinguished from the native peptide by MS, whereas this was not possible with enzyme-linked immunosorbent assay (ELISA).

CONCLUSIONS

Mass spectrometric analysis of culture media can be used to identify the principal peptides produced in response to the stimulation of IEC, and their metabolites. Mass spectrometry provides a comprehensive view of the chemokines and peptides potentially involved in gut inflammation, making it possible to identify the most appropriate peptides for further quantification.

Neutralizing nanobodies targeting diverse chemokines effectively inhibit chemokine function

Chemokine receptors and their ligands play a prominent role in immune regulation but many have also been implicated in inflammatory diseases such as multiple sclerosis, rheumatoid arthritis, allograft rejection after transplantation, and also in cancer metastasis. Most approaches to therapeutically target the chemokine system involve targeting of chemokine receptors with low molecular weight antagonists. Here we describe the selection and characterization of an unprecedented large and diverse panel of neutralizing Nanobodies (single domain camelid antibodies fragment) directed against several chemokines. We show that the Nanobodies directed against CCL2 (MCP-1), CCL5 (RANTES), CXCL11 (I-TAC), and CXCL12 (SDF-1α) bind the chemokines with high affinity (at nanomolar concentration), thereby blocking receptor binding, inhibiting chemokine-induced receptor activation as well as chemotaxis. Together, we show that neutralizing Nanobodies can be selected efficiently for effective and specific therapeutic treatment against a wide range of immune and inflammatory diseases.

Chemerin is an antimicrobial agent in human epidermis

Chemerin, a chemoattractant ligand for chemokine-like receptor 1 (CMKLR1) is predicted to share similar tertiary structure with antibacterial cathelicidins. Recombinant chemerin has antimicrobial activity. Here we show that endogenous chemerin is abundant in human epidermis, and that inhibition of bacteria growth by exudates from organ cultures of primary human skin keratinocytes is largely chemerin-dependent. Using a panel of overlapping chemerin-derived synthetic peptides, we demonstrate that the antibacterial activity of chemerin is primarily mediated by Val⁶⁶-Pro⁸⁵, which causes direct bacterial lysis. Therefore, chemerin is an antimicrobial agent in human skin.

Preparation of C-terminally modified chemokines by expressed protein ligation

In order to link structural features on a molecular level to the function of chemokines, site-specific modification strategies are strongly required. These can be used to incorporate fluorescent dyes and/or physical probes to allow investigations in a wide range of biological and physical techniques, e.g., nuclear magnetic resonance (NMR) spectroscopy, fluorescence microscopy, fluorescence resonance energy transfer (FRET), or fluorescence correlation spectroscopy (FCS). Only a limited number of functional groups within the 20 canonical amino acids allow ligation strategies that can be helpful to introduce novel functionalities, which in turn expand the scope of chemoselective and orthogonal reactivity of (semi)synthetic chemokines. In the present chapter we mainly focus on the fabulous history of native chemical ligation (NCL) and provide a general protocol for the preparation of C-terminally modified SDF-1α including tips and tricks for practical work. We believe that this protocol can be easily adapted to other chemokines and many proteins in general.

The N-terminal ectodomain of Ninjurin1 liberated by MMP9 has chemotactic activity

Ninjurin1 is known as an adhesion molecule promoting leukocyte trafficking under inflammatory conditions. However, the posttranslational modifications of Ninjurin1 are poorly understood. Herein, we defined the proteolytic cleavage of Ninjurin1 and its functions. HEK293T cells overexpressing the C- or N-terminus tagging mouse Ninjurin1 plasmid produced additional cleaved forms of Ninjurin1 in the lysates or conditioned media (CM). Two custom-made anti-Ninjurin1 antibodies, Ab(1-15) or Ab(139-152), specific to the N- or C-terminal regions of Ninjurin1 revealed the presence of its shedding fragments in the mouse liver and kidney lysates. Furthermore, Matrix Metalloproteinase (MMP) 9 was responsible for Ninjurin1 cleavage between Leu(56) and Leu(57). Interestingly, the soluble N-terminal Ninjurin1 fragment has structural similarity with well-known chemokines. Indeed, the CM from HEK293T cells overexpressing the GFP-mNinj1 plasmid was able to attract Raw264.7 cells in trans-well assay. Collectively, we suggest that the N-terminal ectodomain of mouse Ninjurin1, which may act as a chemoattractant, is cleaved by MMP9.

Subversion of cytokine networks by virally encoded decoy receptors

During the course of evolution, viruses have captured or created a diverse array of open reading frames, which encode for proteins that serve to evade and sabotage the host innate and adaptive immune responses that would otherwise lead to their elimination. These viral genomes are some of the best textbooks of immunology ever written. The established arsenal of immunomodulatory proteins encoded by viruses is large and growing, and includes specificities for virtually all known inflammatory pathways and targets. The focus of this review is on herpes and poxvirus-encoded cytokine and chemokine-binding proteins that serve to undermine the coordination of host immune surveillance. Structural and mechanistic studies of these decoy receptors have provided a wealth of information, not only about viral pathogenesis but also about the inner workings of cytokine signaling networks.

Chemokine receptor oligomerization: a further step toward chemokine function

A broad array of biological responses including cell polarization, movement, immune and inflammatory responses, as well as prevention of HIV-1 infection, are triggered by the chemokines, a family of secreted and structurally related chemoattractant proteins that bind to class A-specific seven-transmembrane receptors linked to G proteins. Chemokines and their receptors should not be considered isolated entities, as they act in complex networks. Chemokines bind as oligomers, or oligomerize after binding to glycosaminoglycans on endothelial cells, and are then presented to their receptors on target cells, facilitating the generation of chemoattractant gradients. The chemokine receptors form homo- and heterodimers, as well as higher order structures at the cell surface. These structures are dynamic and are regulated by receptor expression and ligand levels. Complexity is even greater, as in addition to regulation by cytokines and decoy receptors, chemokine and receptor levels are affected by proteolytic cleavage and other protein modifications. This complex scenario should be considered when analyzing chemokine biology and the ability of their antagonists to act in vivo. Strategies based on blocking or stabilizing ligand and receptor dimers could be alternative approaches that might have broad therapeutic potential.

Chemerin: a potential endocrine link between obesity and type 2 diabetes

Obesity and type 2 diabetes have reached epidemic levels and account for a substantial portion of the annual health expenditures of developed nations. While there is an abundance of epidemiological evidence demonstrating that obesity is a primary risk factor for developing type 2 diabetes, the mechanism(s) underlying this linkage are not completely understood. Given the enormous impact of these disorders on global health, considerable research effort has been devoted to elucidate the pathophysiological relationship between these two disorders. Two factors believed to contribute to the causal link between obesity and type 2 diabetes are chronic inflammation and altered secretion of adipose-derived signaling molecules (adipokines). Independent lines of investigation have implicated the novel adipokine chemerin as a regulator of adipogenesis, inflammation, and glucose metabolism through interactions with the cognate cell surface receptor chemokine-like receptor 1. Increased levels of chemerin that occur with obesity are hypothesized to be a causal factor in the development of type 2 diabetes as a consequence of dysregulation of the key physiological processes regulated by this adipokine. This review summarizes current research on the biological roles of chemerin and chemokine-like receptor 1, and highlights key questions to guide future research on the role of this adipokine in mediating obesity and the development of type 2 diabetes.

Ion mobility mass spectrometry coupled with rapid protein threading predictor structure prediction and collision-induced dissociation for probing chemokine conformation and stability

Unique to ion mobility mass spectrometry (IM-MS) is the ability to provide collision cross section (CCS) data and the capacity to delineate any dissociation and/or unfolding of protein complexes. The strong correlation of the experimentally determined CCS with theory is indicative of the retention of native structure in the gas phase, which in turn, qualifies as a means in evaluating the IM-MS data. The assessment of IM-MS data, however, is currently impeded due to the lack of appropriate structural coordinates to use as input in the in silico calculation of theory. To address this issue, this study involves the use of rapid protein threading predictor (RAPTOR) to generate tertiary structures of closely related monomeric chemokines (MCP-1, MCP-3, MCP-4, and eotaxin) and, subsequently, utilize these models to estimate the theoretical values. Experimental CCS of both the model proteins and chemokines correlate well with theory generated by RAPTOR. All conformations for z = 5+ of chemokines fall within theoretical limits. Of the four chemokines, MCP-4 with z = 6+ appears to adopt an extended conformation, while eotaxin gradually unfolds, and the extended structures of MCP-1 and MCP-3 increase in abundance upon activation. Combining RAPTOR with IM-MS and collision-induced dissociation (CID) enables us to interrogate the conformations of homologous proteins with very similar tertiary structures.

Identification of CMTM7 as a transmembrane linker of BLNK and the B-cell receptor

BLNK is a pivotal adaptor protein in the signal transduction pathway from the IgM class B-cell receptor. BLNK is phosphorylated by Syk and binds various signaling intermediates, leading to cellular events including MAP-kinase activation, culminating in cellular activation. It remains unclear how BLNK is initially recruited to the surface IgM (sIgM) complex to which Syk is also recruited. Here we show that CMTM7, a tetra-spanning membrane protein of unknown function, co-localized with clathrin and sIgM at the plasma membrane. RNA-interference-mediated knockdown of CMTM7 expression in B cells resulted in an impairment of sIgM-ligation-induced tyrosine phosphorylation of BLNK, which was due to an impaired interaction of BLNK and Syk, and in a failure to activate JNK and ERK, but not upstream kinases such as Src-family kinases and Syk. CMTM7 was bound to BLNK in a membrane fraction, and their association was augmented after sIgM ligation. Exogenous CMTM7 or a mutant with an N-terminal deletion (ΔN), but not one with a C-terminal deletion (ΔC) that is defective in membrane localization, were able to restore BLNK-Syk binding, BLNK phosphorylation and ERK activation in the CMTM7-knockdown B cells. In addition, CMTM7 and the ΔN, but not the ΔC, were constitutively associated with sIgM, and this binding was required for BLNK recruitment to sIgM. From these data, we conclude that CMTM7 functions to link sIgM and BLNK in the plasma membrane, to recruit BLNK to the vicinity of Syk, and to initiate the BLNK-mediated signal transduction.

[The mechanism of polypeptide derived from viral macrophage inflammatory protein II modulates SDF-1α/CXCR4-induced migration]

AIM

To assess whether NT21MP, the synthetic antagonist 21-mer peptide derived from viral macrophage inflammatory protein II inhibits human SKBR3 cells migration by interfering with SDF-1α/CXCR4 signaling.

METHODS

The levels of CXCR4 were detected in breast cancer cells SKBR3 and MCF-7 by RT-PCR and immunohistochemistry. The effect of SDF-1α-induced SKBR3 migration (chemotaxis) in the presence and absence of NT21MP was determined using the Boyden chamber migration assay. Intracellular Ca(2+); concentration was measured by fluorometric analysis. Western blot analyses were performed to quantify phosphorylated ERK1/2 and FAK expression levels.

RESULTS

The expression of CXCR4 was higher in SKBR3 than MCF-7 cells; SKBR3 migration increased in SDF-1α-treated cells. In contrast, AMD3100, an inhibitor of CXCR4 effectively inhibited SKBR3 migration. SKBR3 migration was decreased when the cells were exposed to NT21MPdose dependently(P<0.05). NT21MP also blocked Ca(2+); influx(P<0.05), an important signal for SKBR3 migration. In addition, NT21MP significantly decreased SDF-1α-induced SKBR3 migration and downregulated SDF-1α-induced express of phospho-ERK1/2 and phospho-FAK(P<0.05).

CONCLUSION

The results showed that NT21MP has an inhibitory effect on SDF-1α-induced SKBR3 migration. The plausible mechanism of action could be upstream blockage of Ca(2+); influx and the downstream reduction of ERK1/2 and FAK signals.

Engineering chemoattractant gradients using chemokine-releasing polysaccharide microspheres

Spatial and temporal concentration gradients of chemoattractants direct many biological processes, especially the guidance of immune cells to tissue sites during homeostasis and responses to infection. Such gradients are ultimately generated by secretion of attractant proteins from single cells or collections of cells. Here we describe cell-sized chemoattractant-releasing polysaccharide microspheres, capable of mimicking chemokine secretion by host cells and generating sustained bioactive chemokine gradients in their local microenvironment. Exploiting the common characteristic of net cationic charge and reversible glycosaminoglycan binding exhibited by many chemokines, we synthesized alginate hydrogel microspheres that could be loaded with several different chemokines (including CCL21, CCL19, CXCL12, and CXCL10) by electrostatic adsorption. These polysaccharide microspheres subsequently released the attractants over periods ranging from a few hours to at least 1 day when placed in serum-containing medium or collagen gels. The generated gradients were able to attract cells more than hundreds of microns away to make contact with individual microspheres. This versatile system for chemoattractant delivery could find applications in immunotherapy, vaccines and fundamental chemotaxis studies in vivo and in vitro.

Novel peptides based on HIV-1 gp120 sequence with homology to chemokines inhibit HIV infection in cell culture

The sequential interaction of the envelope glycoprotein of the human immunodeficiency virus type 1 (HIV-1) with CD4 and certain chemokine coreceptors initiates host cell entry of the virus. The appropriate chemokines have been shown to inhibit viral replication by blocking interaction of the gp120 envelope protein with the coreceptors. We considered the possibility that this interaction involves a motif of the gp120 that may be structurally homologous to the chemokines. In the amino acid sequences of most chemokines there is a Trp residue located at the beginning of the C-terminal α-helix, which is separated by six residues from the fourth Cys residue. The gp120 of all HIV-1 isolates have a similar motif, which includes the C-terminal part of a variable loop 3 (V3) and N-terminal part of a conserved region 3 (C3). Two synthetic peptides, derived from the relevant gp120 sequence inhibited HIV-1 replication in macrophages and T lymphocytes in sequence-dependent manner. The peptides also prevented binding of anti-CXCR4 antibodies to CXCR4, and inhibited the intracellular Ca²⁺ influx in response to CXCL12/SDF-1α. Thus these peptides can be used to dissect gp120 interactions with chemokine receptors and could serve as leads for the design of new inhibitors of HIV-1.

Chemerin: at the crossroads of inflammation and obesity

Chemerin is a secreted protein with a complex but well-established role in immune function. Parallel lines of investigation also support the notion that chemerin is a novel adipokine that regulates adipocyte development and metabolic function as well as glucose metabolism in liver and skeletal muscle tissues. A growing body of human experimental data indicates that serum chemerin levels are elevated in patients with obesity and that they exhibit a positive correlation with various aspects of the metabolic syndrome. Thus, the dual role of chemerin in inflammation and metabolism might provide a link between chronic inflammation and obesity, as well as obesity-related disorders such as type 2 diabetes and cardiovascular disease.

Integrin and chemokine receptor gene expression in implant-adherent cells during early osseointegration

The mechanisms of early cellular recruitment and interaction to titanium implants are not well understood. The aim of this study was to investigate the expression of pro-inflammatory cytokines, chemokines and adhesion markers during the first 24 h of implantation. Anodically oxidized and machined titanium implants were inserted in rat tibia. After 3, 12, and 24 h the implants were unscrewed and analyzed with quantitative polymerase chain reaction. Immunohistochemistry and scanning electron microscopy revealed different cell types, morphology and adhesion at the two implant surfaces. A greater amount of cells, as indicated by higher expression of small subunit ribosomal RNA (18S), was detected on the oxidized surface. Higher expression of CXC chemokine receptor-4 (at 12 h) and integrins, alphav (at 12 h), beta1 (at 24 h) and beta2 (at 12 and 24 h) was detected at the oxidized surfaces. Significantly higher tumor necrosis factor-alpha (at 3 h) and interleukin-1beta (at 24 h) expression was demonstrated for the machined surface. It is concluded that material surface properties rapidly modulate the expression of receptors important for the recruitment and adhesion of cells which are crucial for the inflammatory and regenerative processes at implant surfaces in vivo.

Proteolytic regulatory mechanism of chemerin bioactivity

Chemerin is a novel chemoattractant recognized by chemokine-like receptor 1 (CMKLR1), a serpentine receptor expressed primarily by plasmacytoid dendritic cells, natural killer cells, and macrophages. Human prochemerin circulates in plasma as an inactive precursor. Its chemotactic activity is expressed upon cleavage of the C-terminal amino acid residues by proteases of the coagulation, fibrinolytic, and inflammatory system. The C-terminal cleavage site of prochemerin is highly conservative, indicating that the proteolytic regulation of chemerin bioactivity is a common mechanism undertaken by different species. In this review, we summarized chemerin-proteases interactions, chemerin receptors, and their importance in normal and pathologic conditions.

SB265610 is an allosteric, inverse agonist at the human CXCR2 receptor

BACKGROUND AND PURPOSE

In several previous studies, the C-X-C chemokine receptor (CXCR)2 antagonist 1-(2-bromo-phenyl)-3-(7-cyano-3H-benzotriazol-4-yl)-urea (SB265610) has been described as binding competitively with the endogenous agonist. This is in contrast to many other chemokine receptor antagonists, where the mechanism of antagonism has been described as allosteric.

EXPERIMENTAL APPROACH

To determine whether it displays a unique mechanism among the chemokine receptor antagonists, the mode of action of SB265610 was investigated at the CXCR2 receptor using radioligand and [(35)S]-GTPgammaS binding approaches in addition to chemotaxis of human neutrophils.

KEY RESULTS

In equilibrium saturation binding studies, SB265610 depressed the maximal binding of [(125)I]-interleukin-8 ([(125)I]-IL-8) without affecting the K(d). In contrast, IL-8 was unable to prevent binding of [(3)H]-SB265610. Kinetic binding experiments demonstrated that this was not an artefact of irreversible or slowly reversible binding. In functional experiments, SB265610 caused a rightward shift of the concentration-response curves to IL-8 and growth-related oncogene alpha, but also a reduction in maximal response elicited by each agonist. Fitting these data to an operational allosteric ternary complex model suggested that, once bound, SB265610 completely blocks receptor activation. SB265610 also inhibited basal [(35)S]-GTPgammaS binding in this preparation.

CONCLUSIONS AND IMPLICATIONS

Taken together, these data suggest that SB265610 behaves as an allosteric inverse agonist at the CXCR2 receptor, binding at a region distinct from the agonist binding site to prevent receptor activation, possibly by interfering with G protein coupling.

Chemokine receptor-derived peptides as multi-target drug leads for the treatment of inflammatory diseases

The rationale for multi-target drugs has been strengthened both on theoretical and empirical grounds. Serious diseases that are intractable to treatment were found to have multiple pathogenic factors and examples of successful drugs were shown to affect multiple disease targets. The salient features of multiple-target drugs, low target affinity and rapid binding kinetics, have been responsible for their late discovery and slow development. We predicted that peptides from the ligand-binding domains of chemokine (CK) receptors could be used to modulate the activities of disease-related chemokines (CKs) for therapeutic effect. We developed innovative technologies to produce, screen and optimize low affinity, chemokine-binding peptides (CBPs) derived from chemokine receptors (CRs). The peptides were found to have therapeutic activity in animal models of disease, confirming our prediction and validating the related technologies.

An engineered monomer of CCL2 has anti-inflammatory properties emphasizing the importance of oligomerization for chemokine activity in vivo

We demonstrated recently that P8A-CCL2, a monomeric variant of the chemokine CCL2/MCP-1, is unable to induce cellular recruitment in vivo, despite full activity in vitro. Here, we show that this variant is able to inhibit CCL2 and thioglycollate-mediated recruitment of leukocytes into the peritoneal cavity and recruitment of cells into lungs of OVA-sensitized mice. This anti-inflammatory activity translated into a reduction of clinical score in the more complex inflammatory model of murine experimental autoimmune encephalomyelitis. Several hypotheses for the mechanism of action of P8A-CCL2 were tested. Plasma exposure following s.c. injection is similar for P8A-CCL2 and wild-type (WT) CCL2, ruling out the hypothesis that P8A-CCL2 disrupts the chemokine gradient through systemic exposure. P8A-CCL2 and WT induce CCR2 internalization in vitro and in vivo; CCR2 then recycles to the cell surface, but the cells remain refractory to chemotaxis in vitro for several hours. Although the response to P8A-CCL2 is similar to WT, this finding is novel and suggests that despite the presence of the receptor on the cell surface, coupling to the signaling machinery is retarded. In contrast to CCL2, P8A-CCL2 does not oligomerize on glycosaminoglycans (GAGs). However, it retains the ability to bind GAGs and displaces endogenous JE (murine MCP-1) from endothelial surfaces. Intravital microscopy studies indicate that P8A-CCL2 prevents leukocyte adhesion, while CCL2 has no effect, and this phenomenon may be related to the mechanism. These results suggest that oligomerization-deficient chemokines can exhibit anti-inflammatory properties in vivo and may represent new therapeutic modalities.

Protein coding content of the UL)b' region of wild-type rhesus cytomegalovirus

A recent comparison of two rhesus cytomegalovirus (RhCMV) genomes revealed that the region at the right end of the U(L) genome component (U(L)b') undergoes genetic alterations similar to those observed in serially passaged human cytomegalovirus (HCMV). To determine the coding content of authentic wild-type RhCMV in this region, the U(L)b' sequence was amplified from virus obtained from naturally infected rhesus macaques without passage in vitro. A total of 24 open reading frames (ORFs) potentially encoding >99 amino acid residues were identified, 10 of which are related to HCMV ORFs and 15 to previously listed RhCMV ORFs. In addition, the analysis revealed a cluster of three novel alpha chemokine-like ORFs, bringing the number of predicted alpha chemokine genes in this region to six. Three of these six genes exhibit a high level of sequence diversity, as has been observed for the HCMV alpha chemokine gene UL146.

Molecular cloning and functional characterization of porcine CCL28: Possible involvement in homing of IgA antibody secreting cells into the mammary gland

Constitutive expression of chemokines by epithelial cells controls the recruitment and the localization of specialized lymphocytes. Mucosae associated-epithelial chemokine (MEC/CCL28) cloned from porcine salivary gland and colon tissues consisted of an open reading frame (ORF) of 384-bp coding for 127 amino-acids protein with 22 residues signal sequence. The resulting mature protein is composed of 105 aa with 4 conserved cysteine residues. CCL28 shows aa sequence identity with rat, mouse, macaque and human ranging from 67 to 87%. Using plasmid pQETris-CCL28 injection, a rabbit anti-serum was produced and showed a specific reactivity towards non-reduced form of CCL28 recombinant protein. Comparatively to CCL25 mRNA expression, RT-PCR analysis showed that CCL28 is expressed in various mucosal tissues, but most abundantly in nasal mucosa, colon, salivary and mammary gland (MG). Immunohistochemical analysis showed that CCL28 is produced by epithelial cells of these tissues suggesting that this chemokine can play an important role by linking homing mechanisms between the gut, nasal mucosa and MG. In addition, mRNA of CCL28 was up-regulated in the MG at late gestation and during lactation but was not found at weaning. CCL28 protein was excreted in sow's milk sustaining that this chemokine plays a key role of IgA-ASCs accumulation in this tissue and thus controls the passive transfer level of IgA antibodies from mother to infant.

[Adaptive evolution of chemokines and their receptors genes]

Branch-Site Model is a statistical method for detecting molecular adaptation at individual along specific lineages. Not only the model could indicate whether genes in phylogeny under the positive selection or not, but also could forecast positive selection sites in these genes. The sites promote divergence and polymorphism of genes. Chemokines are chemotactic cytokines that can induce immune cells migration, conducting their functions via chemokine receptors. In the test, the molecular adaptation of chemokines and chemokines receptors genes had been analyzed by Branch-Site model. The results showed that only a few of genes, such as RANTES and CCR5, are in the course of positive selection. Several CCR5 positive selection sites are located in a region that involved in binding to receptor and its chemokine.

NMR assignment of human chemerin, a novel chemoattractant

Chemerin is a potent chemoattractant for cells expressing the GPCR CMKLR1, and is thought to play important roles in cell migration and recruitment to sites of tissue damage and inflammation. Here we report the NMR assignments of the 15.6 kDa active form of uniformly (15)N, (13)C labeled chemerin.

Crystal structure and structural mechanism of a novel anti-human immunodeficiency virus and D-amino acid-containing chemokine

Chemokines and their receptors play important roles in normal physiological functions and the pathogeneses of a wide range of human diseases, including the entry of human immunodeficiency virus type 1 (HIV-1). However, the use of natural chemokines to probe receptor biology or to develop therapeutic drugs is limited by their lack of selectivity and the poor understanding of mechanisms in ligand-receptor recognition. We addressed these issues by combining chemical and structural biology in research into molecular recognition and inhibitor design. Specifically, the concepts of chemical biology were used to develop synthetically and modularly modified (SMM) chemokines that are unnatural and yet have properties improved over those of natural chemokines in terms of receptor selectivity, affinity, and the ability to explore receptor functions. This was followed by using structural biology to determine the structural basis for synthetically perturbed ligand-receptor selectivity. As a proof-of-principle for this combined chemical and structural-biology approach, we report a novel D-amino acid-containing SMM-chemokine designed based on the natural chemokine called viral macrophage inflammatory protein II (vMIP-II). The incorporation of unnatural D-amino acids enhanced the affinity of this molecule for CXCR4 but significantly diminished that for CCR5 or CCR2, thus yielding much more selective recognition of CXCR4 than wild-type vMIP-II. This D-amino acid-containing chemokine also showed more potent and specific inhibitory activity against HIV-1 entry via CXCR4 than natural chemokines. Furthermore, the high-resolution crystal structure of this D-amino acid-containing chemokine and a molecular-modeling study of its complex with CXCR4 provided the structure-based mechanism for the selective interaction between the ligand and chemokine receptors and the potent anti-HIV activity of D-amino acid-containing chemokines.

Chemokine: receptor structure, interactions, and antagonism

Chemokines are critical mediators of cell migration during routine immune surveillance, inflammation, and development. Chemokines bind to G protein-coupled receptors and cause conformational changes that trigger intracellular signaling pathways involved in cell movement and activation. Although chemokines evolved to benefit the host, inappropriate regulation or utilization of these proteins can contribute to or cause many diseases. Specific chemokine receptors provide the portals for HIV to get into cells, and others contribute to inflammatory diseases and cancer. Thus, there is significant interest in developing receptor antagonists. To this end, the structures of ligands coupled with mutagenesis studies have revealed mechanisms for antagonism based on modified proteins. Although little direct structural information is available on the receptors, binding of small molecules to mutant receptors has allowed the identification of key residues involved in the receptor-binding pockets. In this review, we discuss the current knowledge of chemokine:receptor structure and function, and its contribution to drug discovery.

Time- and temperature-dependent acetylation of the chemokine RANTES produced in recombinant Escherichia coli

The S24F mutant of the chemokine RANTES was found to be partly acetylated when produced in recombinant Escherichia coli BL21(DE3)(pDIA17)(CCL5-S24F-pET-26b). Mass spectrometry and Edman sequencing of peptides generated by lys-C endopeptidase indicated that Lys-26, Lys-34, Lys-46, and Lys-57 were susceptible to acetylation. The extent of acetylation of the RANTES S24F polypeptide increased with temperature and with the time during which the culture was incubated after adding the inducer isopropyl-beta-D-thiogalactoside (IPTG). These findings suggest that induction at low temperature and for a short period of time should be preferred when spurious acetylation is a problem for the production of genuine recombinant polypeptides. Acetylation of the polypeptide was not affected by deleting acs, yfiQ, or speG, which encode acetyl-CoA synthetase, acetyl-CoA synthetase acetylase, and spermidine acetyl transferase, respectively, nor by the presence or absence of the pDIA17 plasmid, which harbours the cat gene encoding chloramphenicol acetyl transferase. By contrast, spontaneous acetylation of RANTES could be demonstrated by incubating either the purified polypeptide or inclusion bodies derived from an induced culture in the presence of acetyl-CoA.

Transmembrane chemokines: versatile 'special agents' in vascular inflammation

Within the chemokine family of small chemotactic polypeptides CX3CL1 (fractalkine) and CXCL16 (SR-PSOX) are exceptional in that they are synthesized as transmembrane molecules and can be cleaved from the cell surface to produce a soluble chemoattractant. As transmembrane molecules on the surface of endothelial cells, CX3CL1 and CXCL16 can interact with their receptors CX3CR1 and CXCR6, respectively, which are expressed on leukocyte subtypes. This interaction leads to cell-cell adhesion that is resistant to shear forces. Transmembrane CX3CL1 and CXCL16 are constitutively shed from the cell surface by the activity of a disintegrin and metalloproteinase (ADAM) 10, and cleavage can be rapidly enhanced by activation of the closely related enzyme ADAM17. This cleavage leads to the downregulation of adhesive properties and may even result in the detachment of bound cells. Functionally, both chemokines appear to exert homeostatic and inflammatory activities. Basal expression of CX3CL1 or CXCL16 may be relevant for positioning and survival of tissue-homing leukocytes. Upregulated expression is found under inflammatory conditions such as atherosclerosis where CXCL16 may have a dual function by acting as an adhesion molecule and by promoting uptake of oxidized LDL as a scavenger receptor. Accumulating evidence from knockout mice and genetic polymorphisms in humans points towards a differential contribution of CX3CL1 and CXCL16 in atherosclerosis, where shedding may serve to further regulate their biological functions. Small molecules that block either the receptors or the shedding enzymes of transmembrane chemokines need to be tested in animal models of vascular inflammation.

Chemokines and chemokine receptors in the brain: implication in neuroendocrine regulation

Chemokines are small secreted proteins that chemoattract and activate immune and non-immune cells both in vivo and in vitro. In addition to their well-established role in the immune system, several recent reports have suggested that chemokines and their receptors may also play a role in the central nervous system (CNS). The best known central action is their ability to act as immunoinflammatory mediators. Indeed, these proteins regulate leukocyte infiltration in the brain during inflammatory and infectious diseases. However, we and others recently demonstrated that they are expressed not only in neuroinflammatory conditions, but also constitutively by different cell types including neurons in the normal brain, suggesting that they may act as modulators of neuronal functions. The goal of this review is to highlight the role of chemokines in the control of neuroendocrine functions. First, we will focus on the expression of chemokines and their receptors in the CNS, with the main spotlight on the neuronal expression in the hypothalamo-pituitary system. Secondly, we will discuss the role--we can now suspect--of chemokines and their receptors in the regulation of neuroendocrine functions. In conclusion, we propose that chemokines can be added to the well-described neuroendocrine regulatory mechanisms, providing an additional fine modulatory tuning system in physiological conditions.

An engineered second disulfide bond restricts lymphotactin/XCL1 to a chemokine-like conformation with XCR1 agonist activity

Chemokines adopt a conserved tertiary structure stabilized by two disulfide bridges and direct the migration of leukocytes. Lymphotactin (Ltn) is a unique chemokine in that it contains only one disulfide and exhibits large-scale structural heterogeneity. Under physiological solution conditions (37 degrees C and 150 mM NaCl), Ltn is in equilibrium between the canonical chemokine fold (Ltn10) and a distinct four-stranded beta-sheet (Ltn40). Consequently, it has not been possible to address the biological significance of each structural species independently. To stabilize the Ltn10 structure in a manner independent of specific solution conditions, Ltn variants containing a second disulfide bridge were designed. Placement of the new cysteines was based on a sequence alignment of Ltn with either the first (Ltn-CC1) or third disulfide (Ltn-CC3) in the CC chemokine, HCC-2. NMR data demonstrate that both CC1 and CC3 retain the Ltn10 chemokine structure and no longer exhibit structural rearrangement. The ability of each mutant to activate the Ltn receptor, XCR1, has been tested using an intracellular Ca2+ flux assay. These data support the conclusion that the chemokine fold of Ltn10 is responsible for receptor activation. We also examined the role of amino- and carboxyl-terminal residues in Ltn-mediated receptor activation. In contrast to previous reports, we find that the 25 residues comprising the novel C-terminal extension do not participate in receptor activation, while the native N-terminus is absolutely required for Ltn function.

Backbone dynamics of SDF-1alpha determined by NMR: interpretation in the presence of monomer-dimer equilibrium

SDF-1alpha is a member of the chemokine family implicated in various reactions in the immune system. The interaction of SDF-1alpha with its receptor, CXCR4, is responsible for metastasis of a variety of cancers. SDF-1alpha is also known to play a role in HIV-1 pathogenesis. The structures of SDF-1alpha determined by NMR spectroscopy have been shown to be monomeric while X-ray structures are dimeric. Biochemical data and in vivo studies suggest that dimerization is likely to be important for the function of chemokines. We report here the dynamics of SDF-1alpha determined through measurement of main chain (15)N NMR relaxation data. The data were obtained at several concentrations of SDF-1alpha and used to determine a dimerization constant of approximately 5 mM for a monomer-dimer equilibrium. The dimerization constant was subsequently used to extrapolate values for the relaxation data corresponding to monomeric SDF-1alpha. The experimental relaxation data and the extrapolated data for monomeric SDF-1alpha were analyzed using the model free approach. The model free analysis indicated that SDF-1alpha is rigid on the nano- to picosecond timescale with flexible termini. Several residues involved in the dimer interface display slow micro- to millisecond timescale motions attributable to chemical exchange such as monomer-dimer equilibrium. NMR relaxation measurements are shown to be applicable for studying oligomerization processes such as the dimerization of SDF-1alpha.

Structural view of glycosaminoglycan–protein interactions

The essential role of protein-glycosaminoglycan interactions in the regulation of various physiological processes has been recognized for several decades but it is only recently that the molecular basis underlying such interactions has emerged. The different methodologies to elucidate the three-dimensional features of glycosaminoglycans along with the interactions with proteins cover high resolution NMR spectroscopy, X-ray crystallography, molecular modeling, and hydrodynamic measurements. The structural results that have accumulated have been organized in databases that allow rapid searching with entries related either to the type of glycosaminoglycan or the type of protein. Finally, three selected examples enlightening the complexity of the nature of the interactions occurring between proteins and glycosaminoglycans are given. The example of interactions between heparin and antithrombin III illustrates how such a complex mechanism as the regulation of blood coagulation by a specific pentasaccharide can be dissected through the combined use of dedicated carbohydrate chemistry and structural glycobiology. The second example deals with the study of complexes between chemokines and heparin, and shows how multimolecular complexes of proteins can be organized in space throughout the action of glycosaminoglycans. Again, the synthesis of chemical mimetics offers an unexpected route to the development of novel glycotherapeutics. Finally, the area of enzymes/glycosaminoglycans complexes is briefly covered to realize the limited knowledge that we have for such an important class of biomacromolecular complexes.