Characterization of the role of the N-loop of MIP-1 beta in CCR5 binding

Host immunogenetics in tick-borne encephalitis virus infection-The CCR5 crossroad

The human Tick-borne encephalitis virus (TBEV) infection is a complex event encompassing factors derived from the virus itself, the vectors, the final host, and the environment as well. Classically, genetic traits stand out among the human factors that modify the susceptibility and progression of infectious diseases. However, and although this is a changing scenario, studies evaluating the genetic factors that affect the susceptibility specifically to TBEV infection and TBEV-related diseases are still scarce. There are already some interesting pieces of evidence showing that some genes and polymorphisms have a real impact on TBEV infection. Also, the inflammatory processes involving tick-human interactions began to be understood in greater detail. This review focuses on the immunogenetic and inflammatory aspects concerning tick-host interactions, TBEV infections, and tick-borne encephalitis. Of note, it has been described that polymorphisms in CD209, GSTM1, IL-10, IL-28B, MMP9, OAS2, OAS3, and TLR3 have a statistically significant impact on TBEV infection. Besides, CCR5, its ligands, and the CCR5Δ32 genetic variant seem to have a very important influence on the infection and its immune responses. Taking this information into consideration, a special discussion regarding the effects of CCR5 on TBEV infection and tick-borne encephalitis will be presented. Emerging topics (such as exosomes, evasins, and CCR5 blockers) involving immunological and inflammatory aspects of TBEV-human interactions will also be addressed. Lastly, the current picture of TBEV infection and the importance to address the TBEV-associated problems through the One Health perspective will be discussed.

Protein engineering of the chemokine CCL20 prevents psoriasiform dermatitis in an IL-23-dependent murine model

Psoriasis is a chronic inflammatory skin disease characterized by the infiltration of T cell and other immune cells to the skin in response to injury or autoantigens. Conventional, as well as unconventional, γδ T cells are recruited to the dermis and epidermis by CCL20 and other chemokines. Together with its receptor CCR6, CCL20 plays a critical role in the development of psoriasiform dermatitis in mouse models. We screened a panel of CCL20 variants designed to form dimers stabilized by intermolecular disulfide bonds. A single-atom substitution yielded a CCL20 variant (CCL20 S64C) that acted as a partial agonist for the chemokine receptor CCR6. CCL20 S64C bound CCR6 and induced intracellular calcium release, consistent with G-protein activation, but exhibited minimal chemotactic activity. Instead, CCL20 S64C inhibited CCR6-mediated T cell migration with nominal impact on other chemokine receptor signaling. When given in an IL-23-dependent mouse model for psoriasis, CCL20 S64C prevented psoriatic inflammation and the up-regulation of IL-17A and IL-22. Our results validate CCR6 as a tractable therapeutic target for psoriasis and demonstrate the value of CCL20 S64C as a lead compound.

Elucidation of the CCR1- and CCR5-binding modes of MIP-1α by application of an NMR spectra reconstruction method to the transferred cross-saturation experiments

C-C chemokine receptor 1 (CCR1) and CCR5 are involved in various inflammation and immune responses, and regulate the progression of the autoimmune diseases differently. However, the number of residues identified at the binding interface was not sufficient to clarify the differences in the CCR1- and CCR5-binding modes to MIP-1α, because the NMR measurement time for CCR1 and CCR5 samples was limited to 24 h, due to their low stability. Here we applied a recently developed NMR spectra reconstruction method, Conservation of experimental data in ANAlysis of FOuRier, to the amide-directed transferred cross-saturation experiments of chemokine receptors, CCR1 and CCR5, embedded in lipid bilayers of the reconstituted high density lipoprotein, and MIP-1α. Our experiments revealed that the residues on the N-loop and β-sheets of MIP-1α are close to both CCR1 and CCR5, and those in the C-terminal helix region are close to CCR5. These results suggest that the genetic influence of the single nucleotide polymorphisms of MIP-1α that accompany substitution of residues in the C-terminal helix region, E57 and V63, would provide clues toward elucidating how the CCR5-MIP-1α interaction affects the progress of autoimmune diseases.

Structural basis of receptor sulfotyrosine recognition by a CC chemokine: the N-terminal region of CCR3 bound to CCL11/eotaxin-1

Trafficking of leukocytes in immune surveillance and inflammatory responses is activated by chemokines engaging their receptors. Sulfation of tyrosine residues in peptides derived from the eosinophil chemokine receptor CCR3 dramatically enhances binding to cognate chemokines. We report the structural basis of this recognition and affinity enhancement. We describe the structure of a CC chemokine (CCL11/eotaxin-1) bound to a fragment of a chemokine receptor: residues 8–23 of CCR3, including two sulfotyrosine residues. We also show that intact CCR3 is sulfated and sulfation enhances receptor activity. The CCR3 sulfotyrosine residues form hydrophobic, salt bridge and cation-p interactions with residues that are highly conserved in CC chemokines. However, the orientation of the chemokine relative to the receptor N terminus differs substantially from those observed for two CXC chemokines, suggesting that initial binding of the receptor sulfotyrosine residues guides subsequent steps in receptor activation, thereby influencing the receptor conformational changes and signaling.

NMR mapping of RANTES surfaces interacting with CCR5 using linked extracellular domains

Chemokines constitute a large family of small proteins that regulate leukocyte trafficking to the site of inflammation by binding to specific cell-surface receptors belonging to the G-protein-coupled receptor (GPCR) superfamily. The interactions between N-terminal (Nt-) peptides of these GPCRs and chemokines have been studied extensively using NMR spectroscopy. However, because of the lower affinities of peptides representing the three extracellular loops (ECLs) of chemokine receptors to their respective chemokine ligands, information concerning these interactions is scarce. To overcome the low affinity of ECL peptides to chemokines, we linked two or three CC chemokine receptor 5 (CCR5) extracellular domains using either biosynthesis in Escherichia coli or chemical synthesis. Using such chimeras, CCR5 binding to RANTES was followed using (1)H-(15)N-HSQC spectra to monitor titration of the chemokine with peptides corresponding to the extracellular surface of the receptor. Nt-CCR5 and ECL2 were found to be the major contributors to CCR5 binding to RANTES, creating an almost closed ring around this protein by interacting with opposing faces of the chemokine. A RANTES positively charged surface involved in Nt-CCR5 binding resembles the positively charged surface in HIV-1 gp120 formed by the C4 and the base of the third variable loop of gp120 (V3). The opposing surface on RANTES, composed primarily of β2-β3 hairpin residues, binds ECL2 and was found to be analogous to a surface in the crown of the gp120 V3. The chemical and biosynthetic approaches for linking GPCR surface regions discussed herein should be widely applicable to the investigation of interactions of extracellular segments of chemokine receptors with their respective ligands.

Solution structure of CCL21 and identification of a putative CCR7 binding site

CCL21 is a human chemokine that recruits normal immune cells and metastasizing tumor cells to lymph nodes through activation of the G protein-coupled receptor CCR7. The CCL21 structure solved by NMR contains a conserved chemokine domain followed by an extended, unstructured C-terminus that is not typical of most other chemokines. A sedimentation equilibrium study showed CCL21 to be monomeric. Chemical shift mapping indicates that the CCR7 N-terminus binds to the N-loop and third β-strand of CCL21's chemokine domain. Details of CCL21-receptor recognition may enable structure-based drug discovery of novel antimetastatic agents.

Classification of anti-HIV compounds using counterpropagation artificial neural networks and decision trees

The main aim of the present work was to collect and categorize anti-HIV molecules in order to identify general structure-activity relationships. In this respect, a total of 5580 drugs and drug-like molecules was collected from 256 different articles published between 1992 and 2010. An algorithm called genetic algorithm-pattern search counterpropagation artificial neural networks (GPS-CPANN) was proposed for the classification of compounds. In addition, the CART (classification and regression trees) method was used for construction of decision trees and finding the best molecular descriptors. The results revealed that the developed CPANN models and decision tree can correctly classify the molecules according to their inhibition mechanisms and activities. Some general parameters such as molecular weight, average molecular weight, number of hydrogen atoms and number of hydroxyl groups were found to be important for describing the inhibition behaviour of anti-HIV agents. The developed classifier models in this work can be used to screen large libraries of compounds to identify those likely to display activity as anti-HIV agents.

Structural basis of chemokine sequestration by CrmD, a poxvirus-encoded tumor necrosis factor receptor

Pathogens have evolved sophisticated mechanisms to evade detection and destruction by the host immune system. Large DNA viruses encode homologues of chemokines and their receptors, as well as chemokine-binding proteins (CKBPs) to modulate the chemokine network in host response. The SECRET domain (smallpox virus-encoded chemokine receptor) represents a new family of viral CKBPs that binds a subset of chemokines from different classes to inhibit their activities, either independently or fused with viral tumor necrosis factor receptors (vTNFRs). Here we present the crystal structures of the SECRET domain of vTNFR CrmD encoded by ectromelia virus and its complex with chemokine CX3CL1. The SECRET domain adopts a β-sandwich fold and utilizes its β-sheet I surface to interact with CX3CL1, representing a new chemokine-binding manner of viral CKBPs. Structure-based mutagenesis and biochemical analysis identified important basic residues in the 40s loop of CX3CL1 for the interaction. Mutation of corresponding acidic residues in the SECRET domain also affected the binding for other chemokines, indicating that the SECRET domain binds different chemokines in a similar manner. We further showed that heparin inhibited the binding of CX3CL1 by the SECRET domain and the SECRET domain inhibited RAW264.7 cell migration induced by CX3CL1. These results together shed light on the structural basis for the SECRET domain to inhibit chemokine activities by interfering with both chemokine-GAG and chemokine-receptor interactions.

Chemokines are a family of small proteins that help the immune system fight against invading pathogens by inducing the white blood cells to the areas of infection and inflammation. Due to the important roles of chemokines in immune response, the pathogens evolve diverse mechanisms to neutralize their activities. One example is that large DNA viruses, such as poxviruses and herpesviruses can produce chemokine binding proteins (CKBPs) to sequester chemokines during the infection. The SECRET domain represents a new family of viral CKBPs that was originally identified as a C-terminal extension of the viral tumor necrosis factor receptors (vTNFRs). We determined the three-dimensional structures of the SECRET domain and its complex with chemokine CX3CL1, revealing a new chemokine-binding manner of viral CKBPs. We also showed that other chemokines from different classes may be bound by the SECRET domain in a way similar to that observed in the SECRET/CX3CL1 complex structure. Our biochemical and chemotaxis assays also suggest that the SECRET domain is able to interfere with both chemokine-GAG and chemokine-receptor interactions, both of which are essential for chemokine activities in vivo.

Biology and clinical relevance of chemokines and chemokine receptors CXCR4 and CCR5 in human diseases

Chemokines and their receptors are implicated in a wide range of human diseases, including acquired immune deficiency syndrome (AIDS). The entry of human immunodeficiency virus type 1 (HIV-1) into a cell is initiated by the interaction of the virus's surface envelope proteins with two cell surface components of the target cell, namely CD4 and a chemokine co-receptor, usually CXCR4 or CCR5. Typical anti-HIV-1 agents include protease and reverse transcriptase inhibitors, but the targets of these agents tend to show rapid mutation rates. As such, strategies based on HIV-1 co-receptors have appeal because they target invariant host determinants. Chemokines and their receptors are also of general interest since they play important roles in numerous physiological and pathological processes in addition to AIDS. Therefore, intensive basic and translational research is ongoing for the dissection of their structure - function relationships in an effort to understand the molecular mechanism of chemokine - receptor interactions and signal transductions across cellular membranes. This paper reviews and discusses recent advances and the translation of new knowledge and discoveries into novel interventional strategies for clinical application.

The chemokine network in acute myelogenous leukemia: molecular mechanisms involved in leukemogenesis and therapeutic implications

Acute myelogenous leukemia (AML) is a bone marrow disease in which the leukemic cells show constitutive release of a wide range of CCL and CXCL chemokines and express several chemokine receptors. The AML cell release of various chemokines is often correlated and three release clusters have been identified: CCL2-4/CXCL1/8, CCL5/CXCL9-11, and CCL13/17/22/24/CXCL5. CXCL8 is the chemokine usually released at highest levels. Based on their overall constitutive release profile, patients can be classified into distinct subsets that differ in their T cell chemotaxis towards the leukemic cells. The release profile is modified by hypoxia, differentiation status, pharmacological interventions, and T cell cytokine responses. The best investigated single chemokine in AML is CXCL12 that binds to CXCR4. CXCL12/CXCR4 is important in leukemogenesis through regulation of AML cell migration, and CXCR4 expression is an adverse prognostic factor for patient survival after chemotherapy. Even though AML cells usually release high levels of several chemokines, there is no general increase of serum chemokine levels in these patients and the levels are also influenced by patient age, disease status, chemotherapy regimen, and complicating infections. However, serum CXCL8 levels seem to partly reflect the leukemic cell burden in AML. Specific chemokine inhibitors are currently being developed, although redundancy and pleiotropy of the chemokine system are obstacles in drug development.

Control of feeding behavior in C. elegans by human G protein-coupled receptors permits screening for agonist-expressing bacteria

G protein-coupled receptors (GPCRs) have a key role in many biological processes and are important drug targets for many human diseases. Therefore, understanding the molecular interactions between GPCRs and their ligands would improve drug design. Here, we describe an approach that allows the rapid identification of functional agonists expressed in bacteria. Transgenic Caenorhabditis elegans expressing the human chemokine receptor 5 (CCR5) in nociceptive neurons show avoidance behavior on encounter with the ligand MIP-1alpha and avoid feeding on Escherichia coli expressing MIP-1alpha compared with control bacteria. This system allows a simple activity screen, based on the distribution of transgenic worms in a binary food-choice assay, without a requirement for protein purification or tagging. By using this approach, a library of 68 MIP-1alpha variants was screened, and 13 critical agonist residues involved in CCR5 activation were identified, four of which (T8, A9, N22, and A25) have not been described previously, to our knowledge. Identified residues were subsequently validated in receptor binding assays and by calcium flux assays in mammalian cells. This approach serves not only for structure/function studies as demonstrated, but may be used to facilitate the discovery of agonists within bacterial libraries.

The human CC chemokine MIP-1beta dimer is not competent to bind to the CCR5 receptor

Chemokine dimerization has been the subject of much interest in recent years as evidence has accumulated that different quaternary states of chemokines play different biological roles; the monomer is believed to be the receptor-binding unit, whereas the dimer has been implicated in binding cell surface glycosaminoglycans. However, although several studies have provided evidence for this paradigm by making monomeric chemokine variants or dimer-impaired chemokines, few have provided direct evidence of the receptor function of a chemokine dimer. We have produced a covalent dimer of the CC chemokine macrophage inflammatory protein-1beta (MIP-1beta) by placing a disulfide bond at the center of its dimer interface through a single amino acid substitution (MIP-1beta-A10C). This variant was shown to be a nondissociating dimer by SDS-PAGE and analytical ultracentrifugation. NMR reveals a structure largely the same as the wild type protein. In studies of glycosaminoglycan binding, MIP-1beta-A10C binds to a heparin-Sepharose column as tightly as the wild type protein and more tightly than monomeric variants. However, MIP-1beta-A10C neither binds nor activates the MIP-1beta receptor CCR5. It was found that the ability to activate CCR5 was recovered upon reduction of the intermolecular disulfide cross-link by incubation with 1 mm dithiothreitol. This work provides the first definitive evidence that the CC chemokine MIP-1beta dimer is not able to bind or activate its receptor and implicates the CC chemokine monomer as the sole receptor-interacting unit.

Structural basis of chemokine receptor function--a model for binding affinity and ligand selectivity

Chemokine receptors play fundamental roles in human physiology from embryogenesis to inflammatory response. The receptors belong to the G-protein coupled receptor class, and are activated by chemokine ligands with a range of specificities and affinities that result in a complicated network of interactions. The molecular basis for function is largely a black box, and can be directly attributed to the lack of structural information on the receptors. Studies to date indicate that function can be best described by a two-site model, that involves interactions between the receptor N-domain and ligand N-terminal loop residues (site-I), and between receptor extracellular loop and the ligand N-terminal residues (site-II). In this review, we describe how the two-site model could modulate binding affinity and ligand selectivity, and also highlight some of the unique chemokine receptor features, and their role in function.

A310 helical turn is essential for the proliferation-inhibiting properties of macrophage inflammatory protein-1 alpha (CCL3)

Despite possessing marked structural similarities, the chemokines macrophage inflammatory protein-1alpha (MIP-1alpha; CCL3) and RANTES (CCL5) display differential activity in hematopoietic progenitor-cell-inhibitory assays, with MIP-1alpha being active and RANTES inactive in this context. We have sought to identify the key structural determinants of this property of MIP-1alpha. This has involved constructing MIP-1alpha/RANTES chimeras by swapping structural domains between the 2 proteins. Results indicate that, in contrast to other chemokine functions, neither the N nor the C termini are key determinants of inhibitory activity. The motif that appears to be most important for this activity lies between the second and fourth cysteines of MIP-1alpha and further domain swap analysis has narrowed this down to the 3 10 helical turn preceding the first beta-strand in MIP-1alpha. More detailed analysis has highlighted the role played by a specific dipeptide motif in the proliferation-inhibitory activity of chemokines. The involvement of the 3 10 helical-turn motif in chemokine function is unprecedented and this study therefore identifies a novel, functionally essential motif within chemokines. In addition, this study further attests to the alternative mechanisms of action used by MIP-1alpha in inhibition of hematopoietic progenitor-cell proliferation and regulation of leukocyte migration.

Dimerization of chemokine receptors and its functional consequences

It became clear over the recent years that most, if not all, G protein-coupled receptors (GPCR) are able to form dimers or higher order oligomers. Chemokine receptors make no exception to this new rule and both homo- and heterodimerization were demonstrated for CC and CXC receptors. Functional analyses demonstrated negative binding cooperativity between the two subunits of a dimer. The consequence is that only one chemokine can bind with high affinity onto a receptor dimer. In the context of receptor activation, this implies that the motions of helical domains triggered by the binding of agonists induce correlated changes in the other protomer. The impact of the chemokine dimerization process in terms of co-receptor function and drug development is discussed.

Influence of the R22H variant of macrophage inflammatory protein 1beta/Lag-1 in HIV-1 survival

The chemokine macrophage inflammatory protein 1beta/CCL4, ligand of the major HIV co-receptor CCR5, is encoded by two genes, Act-2 and Lag-1. Our work focused on R22H, a variant of Lag-1 located near the N-loop, in the 310 turn, a domain essential for interacting with CCR5. We observed that HIV-1-infected patients from the SEROCO cohort, bearing the R22H variant either at the homozygous or heterozygous state, exhibit a worse global survival compared with wild-type homozygous individuals.

Identification, sequence characterization, and analysis of expression profiles of three novel CC chemokines from domestic duck (Anas platyrhynchos)

Chemokines are low-molecular weight-chemotactic cytokines, which are involved in lymphocyte trafficking and migration of leucocytes to sites of injury, in immune surveillance and in healing process. They also play a role in pathogenesis of inflammatory diseases. Three novel CC chemokines were identified from domestic duck (Anas platyrhynchos) by screening of an enriched cDNA library constructed from mitogen-stimulated splenic mononuclear cells. Two of the clones (AB163 and AB330) had a very high nucleotide (both about 81%) and predicted amino acid level (71 and 76%, respectively) identity to the reported chicken macrophage inflammatory protein 1-beta (MIP-1beta; SCYA4) and regulated upon activation of normal T-cell expressed and secreted (RANTES; SCYA5) sequences. In phylogenetic analysis, these molecules clustered together with corresponding chemokines reported from other vertebrates. The third clone (AB187) had highest homology to chicken MIP-1beta (36% amino acid identity) and showed closer relation to a number of chemokines belonging to monocyte chemoattractant proteins and MIP-1alpha chemokines. Expression of these molecules was upregulated upon mitogen stimulation of splenocytes as detected by semiquantitative RT-PCR. AB187 showed several fold increases (about 8.5 times) in the mRNA expression. Basal level expression of some of these chemokines was detected in both lymphoid and nonlymphoid tissues, including spleen, liver, lung, and bone marrow. Considering the importance of this animal species as a model for diseases such as chronic human hepatitis B, further studies will offer valuable insights into the role of these molecules in immunopathology of such diseases.

Structural Determinants of the Anti-HIV Activity of a CCR5 Antagonist Derived from Toxoplasma gondii

The protozoan parasite Toxoplasma gondii possesses a protein, cyclophilin-18 (C-18), which binds to the chemokine receptor CCR5, induces interleukin-12 production from murine dendritic cells, and inhibits fusion and infectivity of human immunodeficiency virus 1 (HIV-1) R5 viruses by co-receptor antagonism. Site-directed mutagenesis was employed to identify the domains in C-18 responsible for its CCR5 binding and antiviral functions. To do so we focused on amino acid differences with Plasmodium falciparum cyclophilin, which, although 53% identical with C-18, has minimal binding activity for CCR5, and we generated 22 mutants with substitutions in the regions of non-homology located on the putative surface of the molecule. Two mutations situated on the face of C-18, predicted to be involved in its interaction with the ligand cyclosporin A, were shown to be critical for CCR5-binding and the inhibition of HIV-1 fusion and infectivity. In contrast, four mutations in C-18 specifically designed to abolish the peptidyl-prolyl cis-trans-isomerase activity of the protein failed to inactivate its CCR5 binding and HIV inhibitory activities. Interleukin-12 induction by C-18, on the other hand, was abrogated by mutations effecting either the CCR5 binding or enzymatic function of the molecule. These findings shed light on the structural basis of the molecular mimicry of the chemokine function by a pathogen-derived protein and provide a basis for further modification of C-18 into an antiviral agent.

CC and CX3C chemokines differentially interact with the N terminus of the human cytomegalovirus-encoded US28 receptor

Human cytomegalovirus (HCMV) is the causative agent of life-threatening systemic diseases in immunocompromised patients as well as a risk factor for vascular pathologies, like atherosclerosis, in immunocompetent individuals. HCMV encodes a G-protein-coupled receptor (GPCR), referred to as US28, that displays homology to the human chemokine receptor CCR1 and binds several chemokines of the CC family as well as the CX3C chemokine fractalkine with high affinity. Most importantly, following HCMV infection, US28 activates several intracellular pathways, either constitutively or in a chemokine-dependent manner. In this study, our goal was to understand the molecular interactions between chemokines and the HCMV-encoded US28 receptor. To achieve this goal, a double approach has been used, consisting in the analysis of both receptor and ligand mutants. This approach has led us to identify several amino acids located in the N terminus of US28 that differentially contribute to the high affinity binding of CC versus CX3C chemokines. Additionally, our results highlight the importance of secondary modifications occurring at US28, such as sulfation, for ligand recognition. Finally, the effects of chemokine dimerization and interaction with glycosaminoglycans (GAGs) on chemokine binding and activation of US28 were investigated as well using CCL4 as model ligand. In line with the two-state model describing chemokine/receptor interaction, we show that an aromatic residue in the N-loop region of CCL4 promotes tight binding to US28, whereas receptor activation depends on the presence of the N terminus of CCL4, as shown previously for CCR5.

Optimization of gene expression in nonactivated circulating lymphocytes

Circulating lymphocytes are important target cells for the treatment of HIV-related and autoimmune diseases and for stimulating anti-tumor immunity. To date, gene transfection of these nonactivated cells after intravenous delivery of viral or nonviral vectors remains low although these circulating cells are highly accessible. Optimized lentiviral vectors currently can transduce less than 10% of nonactivated circulating lymphocytes. Here we report transfection of up to 15% of these nonactivated cells using liposomes directed to human CCR5 displayed on the surface of helper T cells and macrophages in transgenic mice. Attachment of modified MIP-1 beta to the surface of DNA-liposome complexes increased gene delivery and expression in nonactivated circulating lymphocytes approximately sixfold. In vitro data using these complexes to transfect PM1 cells that have elevated levels of CCR5 supported our data obtained in vivo. Therefore, ligands that bind to cell surface receptors on circulating lymphocytes can be used with optimized systemic liposomes to increase transfection and gene expression in these cells without activation.

The core domain of chemokines binds CCR5 extracellular domains while their amino terminus interacts with the transmembrane helix bundle

CCR5 is a functional receptor for various inflammatory CC-chemokines, including macrophage inflammatory protein (MIP)-1alpha and RANTES (regulated on activation normal T cell expressed and secreted), and is the main coreceptor of human immunodeficiency viruses. The second extracellular loop and amino-terminal domain of CCR5 are critical for chemokine binding, whereas the transmembrane helix bundle is involved in receptor activation. Chemokine domains and residues important for CCR5 binding and/or activation have also been identified. However, the precise way by which chemokines interact with and activate CCR5 is presently unknown. In this study, we have compared the binding and functional properties of chemokine variants onto wild-type CCR5 and CCR5 point mutants. Several mutations in CCR5 extracellular domains (E172A, R168A, K191A, and D276A) strongly affected MIP-1alpha binding but had little effect on RANTES binding. However, a MIP/RANTES chimera, containing the MIP-1alpha N terminus and the RANTES core, bound to these mutants with an affinity similar to that of RANTES. Several CCR5 mutants affecting transmembrane helices 2 and 3 (L104F, L104F/F109H/F112Y, F85L/L104F) reduced the potency of MIP-1alpha by 10-100 fold with little effect on activation by RANTES. However, the MIP/RANTES chimera activated these mutants with a potency similar to that of MIP-1alpha. In contrast, LD78beta, a natural MIP-1alpha variant, which, like RANTES, contains a proline at position 2, activated these mutants as well as RANTES. Altogether, these results suggest that the core domains of MIP-1alpha and RANTES bind distinct residues in CCR5 extracellular domains, whereas the N terminus of chemokines mediates receptor activation by interacting with the transmembrane helix bundle.

The binding surface and affinity of monomeric and dimeric chemokine macrophage inflammatory protein 1 beta for various glycosaminoglycan disaccharides

Chemokines comprise a family of proteins that function in the immune response to recruit leukocytes to sites of infection. This recruitment is believed to be carried out by the establishment of a chemokine gradient by the binding of chemokines to sulfated polysaccharides known as glycosaminoglycans (GAGs) located on the extracellular surface of endothelial cells. In the present studies, multidimensional NMR spectroscopy was used to study the interaction of monomeric and dimeric chemokine macrophage inflammatory protein (MIP)-1 beta variants with a series of differentially sulfated disaccharides. The data define a GAG binding surface, including both basic and uncharged residues such as Arg(18), Asn(23), Val(25), Thr(44), Lys(45), Arg(46), and Ser(47). Dissociation constants determined from these NMR studies consistently show for each disaccharide that dimeric wild type MIP-1 beta binds more tightly than monomeric MIP(9). Furthermore, analysis of the binding surface suggests that participation in the dimer of residues Met(3), Gly(4), and Ser(5) may be responsible for this higher affinity. These studies also indicate that the specificity of MIP-1 beta for particular GAG disaccharides is directly related not only to the degree of disaccharide sulfation but also to the position of the sulfate moiety, with O-sulfation at position 2 of the hexuronic acid unit and position 6 of the D-glucosamine being major determinants for binding.