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Martin P, Kurth EA, Budean D, Momplaisir N, Qu E, Simien JM, Orellana GE, Brautigam CA, Smrcka AV, Haglund E. Biophysical characterization of the CXC chemokine receptor 2 ligands. PLoS One 2024; 19:e0298418. [PMID: 38625857 PMCID: PMC11020491 DOI: 10.1371/journal.pone.0298418] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Accepted: 01/24/2024] [Indexed: 04/18/2024] Open
Abstract
The chemokines of the immune system act as first responders by operating as chemoattractants, directing immune cells to specific locations of inflamed tissues. This promiscuous network is comprised of 50 ligands and 18 receptors where the ligands may interact with the receptors in various oligomeric states i.e., monomers, homodimers, and heterodimers. Chemokine receptors are G-protein coupled receptors (GPCRs) present in the membrane of immune cells. The migration of immune cells occurs in response to a concentration gradient of the ligands. Chemotaxis of neutrophils is directed by CXC-ligand (CXCL) activation of the membrane bound CXC chemokine receptor 2 (CXCR2). CXCR2 plays an important role in human health and is linked to disorders such as autoimmune disorders, inflammation, and cancer. Yet, despite their important role, little is known about the biophysical characteristics controlling ligand:ligand and ligand:receptor interaction essential for biological activity. In this work, we study the homodimers of three of the CXCR2 cognate ligands, CXCL1, CXCL5, and CXCL8. The ligands share high structural integrity but a low sequence identity. We show that the sequence diversity has evolved different binding affinities and stabilities for the CXC-ligands resulting in diverse agonist/antagonist behavior. Furthermore, CXC-ligands fold through a three-state mechanism, populating a folded monomeric state before associating into an active dimer.
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Affiliation(s)
- Patrick Martin
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, United States of America
| | - Emily A. Kurth
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, United States of America
| | - David Budean
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, United States of America
| | - Nathalie Momplaisir
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Elaine Qu
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Jennifer M. Simien
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, United States of America
| | - Grace E. Orellana
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, United States of America
| | - Chad A. Brautigam
- Department of Biophysics and the Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Alan V. Smrcka
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Ellinor Haglund
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, United States of America
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2
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Dürig JN, Schulze C, Bosse M, Penk A, Huster D, Keller S, Rademann J. Dimerization and Crowding in the Binding of Interleukin 8 to Dendritic Glycosaminoglycans as Artificial Proteoglycans. Chemistry 2024; 30:e202302758. [PMID: 38010268 DOI: 10.1002/chem.202302758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Revised: 11/20/2023] [Accepted: 11/21/2023] [Indexed: 11/29/2023]
Abstract
The interactions of glycosaminoglycans (GAG) with proteins of the extracellular matrix govern and regulate complex physiological functions including cellular growth, immune response, and inflammation. Repetitive presentation of GAG binding motifs, as found in native proteoglycans, might enhance GAG-protein binding through multivalent interactions. Here, we report the chemical synthesis of dendritic GAG oligomers constructed of nonasulfated hyaluronan tetrasaccharides for investigating the binding of the protein chemokine interleukin 8 (IL-8) to artificial, well-defined proteoglycan architectures. Binding of mutant monomeric and native dimerizable IL-8 was investigated by NMR spectroscopy and isothermal titration calorimetry. Dendritic oligomerization of GAG increased the binding affinity of both monomeric and dimeric IL-8. Monomeric IL-8 bound to monomeric and dimeric GAG with KD values of 7.3 and 0.108 μM, respectively. The effect was less pronounced for dimerizable wild-type IL-8, for which GAG dimerization improved the affinity from 34 to 5 nM. Binding of dimeric IL-8 to oligomeric GAG was limited by steric crowding effects, strongly reducing the affinity of subsequent binding events. In conclusion, the strongest effect of GAG oligomerization was the amplified binding of IL-8 monomers, which might concentrate monomeric protein in the extracellular matrix and thus promote protein dimerization under physiological conditions.
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Affiliation(s)
- Jan-Niklas Dürig
- Institute of Pharmacy - Medicinal Chemistry, Freie Universität Berlin, Königin-Luise-Str. 2+4, 14195, Berlin, Germany) Corresponding author
| | - Christian Schulze
- Institute of Medical Physics and Biophysics, Leipzig University, Härtelstr. 16/18, 04107, Leipzig, Germany
| | - Mathias Bosse
- Institute of Medical Physics and Biophysics, Leipzig University, Härtelstr. 16/18, 04107, Leipzig, Germany
| | - Anja Penk
- Institute of Medical Physics and Biophysics, Leipzig University, Härtelstr. 16/18, 04107, Leipzig, Germany
| | - Daniel Huster
- Institute of Medical Physics and Biophysics, Leipzig University, Härtelstr. 16/18, 04107, Leipzig, Germany
| | - Sandro Keller
- Biophysics, Institute of Molecular Biosciences (IMB), NAWI Graz, Field of Excellence BioHealth, BioTechMed-Graz, University of Graz, Humboldtstr. 50/III, 8010, Graz, Austria
| | - Jörg Rademann
- Institute of Pharmacy - Medicinal Chemistry, Freie Universität Berlin, Königin-Luise-Str. 2+4, 14195, Berlin, Germany) Corresponding author
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3
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Ishimoto N, Park JH, Kawakami K, Tajiri M, Mizutani K, Akashi S, Tame JRH, Inoue A, Park SY. Structural basis of CXC chemokine receptor 1 ligand binding and activation. Nat Commun 2023; 14:4107. [PMID: 37433790 DOI: 10.1038/s41467-023-39799-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Accepted: 06/29/2023] [Indexed: 07/13/2023] Open
Abstract
Neutrophil granulocytes play key roles in innate immunity and shaping adaptive immune responses. They are attracted by chemokines to sites of infection and tissue damage, where they kill and phagocytose bacteria. The chemokine CXCL8 (also known as interleukin-8, abbreviated IL-8) and its G-protein-coupled receptors CXCR1 and CXCR2 are crucial elements in this process, and also the development of many cancers. These GPCRs have therefore been the target of many drug development campaigns and structural studies. Here, we solve the structure of CXCR1 complexed with CXCL8 and cognate G-proteins using cryo-EM, showing the detailed interactions between the receptor, the chemokine and Gαi protein. Unlike the closely related CXCR2, CXCR1 strongly prefers to bind CXCL8 in its monomeric form. The model shows that steric clashes would form between dimeric CXCL8 and extracellular loop 2 (ECL2) of CXCR1. Consistently, transplanting ECL2 of CXCR2 onto CXCR1 abolishes the selectivity for the monomeric chemokine. Our model and functional analysis of various CXCR1 mutants will assist efforts in structure-based drug design targeting specific CXC chemokine receptor subtypes.
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Affiliation(s)
- Naito Ishimoto
- Drug Design Laboratory, Graduate School of Medical Life Science, Yokohama City University, Tsurumi, Yokohama, 230-0045, Japan
| | - Jae-Hyun Park
- Drug Design Laboratory, Graduate School of Medical Life Science, Yokohama City University, Tsurumi, Yokohama, 230-0045, Japan
| | - Kouki Kawakami
- Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, 980-8578, Japan
| | - Michiko Tajiri
- Structural Epigenetics Laboratory, Graduate School of Medical Life Science, Yokohama City University, Tsurumi, Yokohama, 230-0045, Japan
| | - Kenji Mizutani
- Drug Design Laboratory, Graduate School of Medical Life Science, Yokohama City University, Tsurumi, Yokohama, 230-0045, Japan
| | - Satoko Akashi
- Structural Epigenetics Laboratory, Graduate School of Medical Life Science, Yokohama City University, Tsurumi, Yokohama, 230-0045, Japan
| | - Jeremy R H Tame
- Drug Design Laboratory, Graduate School of Medical Life Science, Yokohama City University, Tsurumi, Yokohama, 230-0045, Japan
| | - Asuka Inoue
- Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, 980-8578, Japan
| | - Sam-Yong Park
- Drug Design Laboratory, Graduate School of Medical Life Science, Yokohama City University, Tsurumi, Yokohama, 230-0045, Japan.
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McKenna S, Giblin SP, Bunn RA, Xu Y, Matthews SJ, Pease JE. A highly efficient method for the production and purification of recombinant human CXCL8. PLoS One 2021; 16:e0258270. [PMID: 34653205 PMCID: PMC8519433 DOI: 10.1371/journal.pone.0258270] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Accepted: 09/22/2021] [Indexed: 12/02/2022] Open
Abstract
Chemokines play diverse and fundamental roles in the immune system and human disease, which has prompted their structural and functional characterisation. Production of recombinant chemokines that are folded and bioactive is vital to their study but is limited by the stringent requirements of a native N-terminus for receptor activation and correct disulphide bonding required to stabilise the chemokine fold. Even when expressed as fusion proteins, overexpression of chemokines in E. coli tends to result in the formation of inclusion bodies, generating the additional steps of solubilisation and refolding. Here we present a novel method for producing soluble chemokines in relatively large amounts via a simple two-step purification procedure with no requirements for refolding. CXCL8 produced by this method has the correct chemokine fold as determined by NMR spectroscopy and in chemotaxis assays was indistinguishable from commercially available chemokines. We believe that this protocol significantly streamlines the generation of recombinant chemokines.
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Affiliation(s)
- Sophie McKenna
- Department of Life Sciences, Imperial College London, London, United Kingdom
| | - Sean Patrick Giblin
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Rosemarie Anne Bunn
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Yingqi Xu
- Department of Life Sciences, Imperial College London, London, United Kingdom
| | | | - James Edward Pease
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
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5
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Fiedler D, Hartl S, Gerlza T, Trojacher C, Kungl A, Khinast J, Roblegg E. Comparing freeze drying and spray drying of interleukins using model protein CXCL8 and its variants. Eur J Pharm Biopharm 2021; 168:152-165. [PMID: 34474111 DOI: 10.1016/j.ejpb.2021.08.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 07/28/2021] [Accepted: 08/19/2021] [Indexed: 10/20/2022]
Abstract
Spray-dried products, such as synthetic peptides and hormones, have already been approved by the U.S. Food and Drug Agency and the European Medicines Agency, while spray-dried antibodies or interleukins, are not yet available on the market. Concerning the latter group, knowledge on whether and how spray-drying (SD) can be performed without adversely affecting their biological activity is lacking. Accordingly, this study aimed at establishing a SD process (Büchi B-90 spray dryer) using three Interleukin-8 based proteins (7-74 kDa) that were dispersed in phosphate buffered saline to maintain their stability. A Box-Behnken Design of Experiments was conducted to identify the appropriate process parameters taking into account the thermal stability of interleukin-8. In parallel, a FD process was developed. Both powders were stored for up to 12 weeks. Powder characterization included residual moisture evaluation and the mean particle size of the SD powder was investigated with Laser Diffraction Analysis. The hydrodynamic volume was measured via size exclusion chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The secondary structure of the model proteins in the solid state was assessed with Fourier-transformation infrared spectroscopy for detecting the protein folding patterns and reconstituted with Circular Dichroism Spectroscopy. Finally, the binding affinity was studied with Surface Plasmon Resonance and Isothermal Fluorescence Titration, the protein stability with Chaotropic Unfolding, and the activity studies were carried out with the chemotaxis assay. The results showed that SD and FD powders with a residual moisture of less than 5 wt% were obtained. The interleukins showed no unfolding upon processing, neither in solid state nor reconstituted. Oligomerization was observed for FD, but not for SD interleukins. However, the unfolding, binding affinity and activity of all interleukins examined did not decrease in neither SD nor FD powders, even after 12 weeks of storage. Thus, it can be concluded that SD of interleukin formulations at outlet temperatures close to ambient temperature is a promising process for transferring them into a stable powder.
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Affiliation(s)
- Daniela Fiedler
- Institute of Process and Particle Engineering, Graz University of Technology, Inffeldgasse 13/III, 8010 Graz, Austria
| | - Sonja Hartl
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical Technology & Biopharmacy, University of Graz, Universitätsplatz 1, 8010 Graz, Austria
| | - Tanja Gerlza
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical Chemistry, University of Graz, Schubertstraße 1, 8010 Graz, Austria
| | - Christina Trojacher
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical Chemistry, University of Graz, Schubertstraße 1, 8010 Graz, Austria
| | - Andreas Kungl
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical Chemistry, University of Graz, Schubertstraße 1, 8010 Graz, Austria
| | - Johannes Khinast
- Institute of Process and Particle Engineering, Graz University of Technology, Inffeldgasse 13/III, 8010 Graz, Austria; Research Center Pharmaceutical Engineering GmbH, Inffeldgasse 13/II, 8010 Graz, Austria
| | - Eva Roblegg
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical Technology & Biopharmacy, University of Graz, Universitätsplatz 1, 8010 Graz, Austria; Research Center Pharmaceutical Engineering GmbH, Inffeldgasse 13/II, 8010 Graz, Austria.
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6
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Rajarathnam K, Schnoor M, Richardson RM, Rajagopal S. How do chemokines navigate neutrophils to the target site: Dissecting the structural mechanisms and signaling pathways. Cell Signal 2019; 54:69-80. [PMID: 30465827 PMCID: PMC6664297 DOI: 10.1016/j.cellsig.2018.11.004] [Citation(s) in RCA: 147] [Impact Index Per Article: 29.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Revised: 11/07/2018] [Accepted: 11/08/2018] [Indexed: 12/12/2022]
Abstract
Chemokines play crucial roles in combating microbial infection and initiating tissue repair by recruiting neutrophils in a timely and coordinated manner. In humans, no less than seven chemokines (CXCL1, CXCL2, CXCL3, CXCL5, CXCL6, CXCL7, and CXCL8) and two receptors (CXCR1 and CXCR2) mediate neutrophil functions but in a context dependent manner. Neutrophil-activating chemokines reversibly exist as monomers and dimers, and their receptor binding triggers conformational changes that are coupled to G-protein and β-arrestin signaling pathways. G-protein signaling activates a variety of effectors including Ca2+ channels and phospholipase C. β-arrestin serves as a multifunctional adaptor and is coupled to several signaling hubs including MAP kinase and tyrosine kinase pathways. Both G-protein and β-arrestin signaling pathways play important non-overlapping roles in neutrophil trafficking and activation. Functional studies have established many similarities but distinct differences for a given chemokine and between chemokines at the level of monomer vs. dimer, CXCR1 vs. CXCR2 activation, and G-protein vs. β-arrestin pathways. We propose that two forms of the ligand binding two receptors and activating two signaling pathways enables fine-tuned neutrophil function compared to a single form, a single receptor, or a single pathway. We summarize the current knowledge on the molecular mechanisms by which chemokine monomers/dimers activate CXCR1/CXCR2 and how these interactions trigger G-protein/β-arrestin-coupled signaling pathways. We also discuss current challenges and knowledge gaps, and likely advances in the near future that will lead to a better understanding of the relationship between the chemokine-CXCR1/CXCR2-G-protein/β-arrestin axis and neutrophil function.
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Affiliation(s)
- Krishna Rajarathnam
- Department of Biochemistry and Molecular Biology, Department of Microbiology and Immunology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, USA.
| | - Michael Schnoor
- Department for Molecular Biomedicine, Cinvestav-IPN, 07360 Mexico City, Mexico
| | - Ricardo M Richardson
- Julius L. Chambers Biomedical/Biotechnology Research Institute, North Carolina Central University, Durham, NC 27707, USA
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7
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Joseph PRB, Spyracopoulos L, Rajarathnam K. Dynamics-Derived Insights into Complex Formation between the CXCL8 Monomer and CXCR1 N-Terminal Domain: An NMR Study. Molecules 2018; 23:E2825. [PMID: 30384436 PMCID: PMC6278376 DOI: 10.3390/molecules23112825] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Revised: 10/19/2018] [Accepted: 10/25/2018] [Indexed: 11/29/2022] Open
Abstract
Interleukin-8 (CXCL8), a potent neutrophil-activating chemokine, exerts its function by activating the CXCR1 receptor that belongs to class A G protein-coupled receptors (GPCRs). Receptor activation involves interactions between the CXCL8 N-terminal loop and CXCR1 N-terminal domain (N-domain) residues (Site-I) and between the CXCL8 N-terminal and CXCR1 extracellular/transmembrane residues (Site-II). CXCL8 exists in equilibrium between monomers and dimers, and it is known that the monomer binds CXCR1 with much higher affinity and that Site-I interactions are largely responsible for the differences in monomer vs. dimer affinity. Here, using backbone 15N-relaxation nuclear magnetic resonance (NMR) data, we characterized the dynamic properties of the CXCL8 monomer and the CXCR1 N-domain in the free and bound states. The main chain of CXCL8 appears largely rigid on the picosecond time scale as evident from high order parameters (S²). However, on average, S² are higher in the bound state. Interestingly, several residues show millisecond-microsecond (ms-μs) dynamics only in the bound state. The CXCR1 N-domain is unstructured in the free state but structured with significant dynamics in the bound state. Isothermal titration calorimetry (ITC) data indicate that both enthalpic and entropic factors contribute to affinity, suggesting that increased slow dynamics in the bound state contribute to affinity. In sum, our data indicate a critical and complex role for dynamics in driving CXCL8 monomer-CXCR1 Site-I interactions.
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Affiliation(s)
- Prem Raj B Joseph
- Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, TX 77555, USA.
- Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555, USA.
| | - Leo Spyracopoulos
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
| | - Krishna Rajarathnam
- Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, TX 77555, USA.
- Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555, USA.
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8
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Rajarathnam K, Sepuru KM, Joseph PRB, Sawant KV, Brown AJ. Glycosaminoglycan Interactions Fine-Tune Chemokine-Mediated Neutrophil Trafficking: Structural Insights and Molecular Mechanisms. J Histochem Cytochem 2018; 66:229-239. [PMID: 29290145 PMCID: PMC5958375 DOI: 10.1369/0022155417739864] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Accepted: 10/10/2017] [Indexed: 01/01/2023] Open
Abstract
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.
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Affiliation(s)
- Krishna Rajarathnam
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas
- Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas
- Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, Texas
| | - Krishna Mohan Sepuru
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas
- Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas
| | - Prem Raj B Joseph
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas
- Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas
| | - Kirti V Sawant
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas
- Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas
| | - Aaron J Brown
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas
- Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas
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9
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Berkamp S, Park SH, De Angelis AA, Marassi FM, Opella SJ. Structure of monomeric Interleukin-8 and its interactions with the N-terminal Binding Site-I of CXCR1 by solution NMR spectroscopy. JOURNAL OF BIOMOLECULAR NMR 2017; 69:111-121. [PMID: 29143165 PMCID: PMC5869024 DOI: 10.1007/s10858-017-0128-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 08/18/2017] [Indexed: 06/07/2023]
Abstract
The structure of monomeric human chemokine IL-8 (residues 1-66) was determined in aqueous solution by NMR spectroscopy. The structure of the monomer is similar to that of each subunit in the dimeric full-length protein (residues 1-72), with the main differences being the location of the N-loop (residues 10-22) relative to the C-terminal α-helix and the position of the side chain of phenylalanine 65 near the truncated dimerization interface (residues 67-72). NMR was used to analyze the interactions of monomeric IL-8 (1-66) with ND-CXCR1 (residues 1-38), a soluble polypeptide corresponding to the N-terminal portion of the ligand binding site (Binding Site-I) of the chemokine receptor CXCR1 in aqueous solution, and with 1TM-CXCR1 (residues 1-72), a membrane-associated polypeptide that includes the same N-terminal portion of the binding site, the first trans-membrane helix, and the first intracellular loop of the receptor in nanodiscs. The presence of neither the first transmembrane helix of the receptor nor the lipid bilayer significantly affected the interactions of IL-8 with Binding Site-I of CXCR1.
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Affiliation(s)
- Sabrina Berkamp
- Department of Chemistry and Biochemistry, University of California, San Diego La Jolla, San Diego, CA, 92093-0307, USA
| | - Sang Ho Park
- Department of Chemistry and Biochemistry, University of California, San Diego La Jolla, San Diego, CA, 92093-0307, USA
| | - Anna A De Angelis
- Department of Chemistry and Biochemistry, University of California, San Diego La Jolla, San Diego, CA, 92093-0307, USA
| | - Francesca M Marassi
- Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, San Diego, CA, 92037, USA
| | - Stanley J Opella
- Department of Chemistry and Biochemistry, University of California, San Diego La Jolla, San Diego, CA, 92093-0307, USA.
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10
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Park SH, Wang V, Radoicic J, De Angelis AA, Berkamp S, Opella SJ. Paramagnetic relaxation enhancement of membrane proteins by incorporation of the metal-chelating unnatural amino acid 2-amino-3-(8-hydroxyquinolin-3-yl)propanoic acid (HQA). JOURNAL OF BIOMOLECULAR NMR 2015; 61:185-96. [PMID: 25430059 PMCID: PMC4398598 DOI: 10.1007/s10858-014-9884-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Accepted: 11/20/2014] [Indexed: 05/16/2023]
Abstract
The use of paramagnetic constraints in protein NMR is an active area of research because of the benefits of long-range distance measurements (>10 Å). One of the main issues in successful execution is the incorporation of a paramagnetic metal ion into diamagnetic proteins. The most common metal ion tags are relatively long aliphatic chains attached to the side chain of a selected cysteine residue with a chelating group at the end where it can undergo substantial internal motions, decreasing the accuracy of the method. An attractive alternative approach is to incorporate an unnatural amino acid that binds metal ions at a specific site on the protein using the methods of molecular biology. Here we describe the successful incorporation of the unnatural amino acid 2-amino-3-(8-hydroxyquinolin-3-yl)propanoic acid (HQA) into two different membrane proteins by heterologous expression in E. coli. Fluorescence and NMR experiments demonstrate complete replacement of the natural amino acid with HQA and stable metal chelation by the mutated proteins. Evidence of site-specific intra- and inter-molecular PREs by NMR in micelle solutions sets the stage for the use of HQA incorporation in solid-state NMR structure determinations of membrane proteins in phospholipid bilayers.
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11
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Joseph PRB, Rajarathnam K. Solution NMR characterization of WT CXCL8 monomer and dimer binding to CXCR1 N-terminal domain. Protein Sci 2014; 24:81-92. [PMID: 25327289 DOI: 10.1002/pro.2590] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Revised: 09/03/2014] [Accepted: 10/10/2014] [Indexed: 01/24/2023]
Abstract
Chemokine CXCL8 and its receptor CXCR1 are key mediators in combating infection and have also been implicated in the pathophysiology of various diseases including chronic obstructive pulmonary disease (COPD) and cancer. CXCL8 exists as monomers and dimers but monomer alone binds CXCR1 with high affinity. CXCL8 function involves binding two distinct CXCR1 sites - the N-terminal domain (Site-I) and the extracellular/transmembrane domain (Site-II). Therefore, higher monomer affinity could be due to stronger binding at Site-I or Site-II or both. We have now characterized the binding of a human CXCR1 N-terminal domain peptide (hCXCR1Ndp) to WT CXCL8 under conditions where it exists as both monomers and dimers. We show that the WT monomer binds the CXCR1 N-domain with much higher affinity and that binding is coupled to dimer dissociation. We also characterized the binding of two CXCL8 monomer variants and a trapped dimer to two different hCXCR1Ndp constructs, and observe that the monomer binds with ∼10- to 100-fold higher affinity than the dimer. Our studies also show that the binding constants of monomer and dimer to the receptor peptides, and the dimer dissociation constant, can vary significantly as a function of pH and buffer, and so the ability to observe WT monomer peaks is critically dependent on NMR experimental conditions. We conclude that the monomer is the high affinity CXCR1 agonist, that Site-I interactions play a dominant role in determining monomer vs. dimer affinity, and that the dimer plays an indirect role in regulating monomer function.
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Affiliation(s)
- Prem Raj B Joseph
- Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, Texas, 77555
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12
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Sepuru KM, Poluri KM, Rajarathnam K. Solution structure of CXCL5--a novel chemokine and adipokine implicated in inflammation and obesity. PLoS One 2014; 9:e93228. [PMID: 24695525 PMCID: PMC3973705 DOI: 10.1371/journal.pone.0093228] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2013] [Accepted: 03/01/2014] [Indexed: 11/19/2022] Open
Abstract
The chemokine CXCL5 is selectively expressed in highly specialized cells such as epithelial type II cells in the lung and white adipose tissue macrophages in muscle, where it mediates diverse functions from combating microbial infections by regulating neutrophil trafficking to promoting obesity by inhibiting insulin signaling. Currently very little is known regarding the structural basis of how CXCL5 mediates its novel functions. Towards this missing knowledge, we have solved the solution structure of the CXCL5 dimer by NMR spectroscopy. CXCL5 is a member of a subset of seven CXCR2-activating chemokines (CAC) that are characterized by the highly conserved ELR motif in the N-terminal tail. The structure shows that CXCL5 adopts the typical chemokine fold, but also reveals several distinct differences in the 30 s loop and N-terminal residues; not surprisingly, crosstalk between N-terminal and 30 s loop residues have been implicated as a major determinant of receptor activity. CAC function also involves binding to highly sulfated glycosaminoglycans (GAG), and the CXCL5 structure reveals a distinct distribution of positively charged residues, suggesting that differences in GAG interactions also influence function. The availability of the structure should now facilitate the design of experiments to better understand the molecular basis of various CXCL5 functions, and also serve as a template for the design of inhibitors for use in a clinical setting.
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Affiliation(s)
- Krishna Mohan Sepuru
- Department of Biochemistry & Molecular Biology, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Krishna Mohan Poluri
- Department of Biochemistry & Molecular Biology, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Krishna Rajarathnam
- Department of Biochemistry & Molecular Biology, University of Texas Medical Branch, Galveston, Texas, United States of America
- Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas, United States of America
- * E-mail:
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13
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Gandhi NS, Mancera RL. Molecular Dynamics Simulations of CXCL-8 and Its Interactions with a Receptor Peptide, Heparin Fragments, and Sulfated Linked Cyclitols. J Chem Inf Model 2011; 51:335-58. [DOI: 10.1021/ci1003366] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Neha S. Gandhi
- Curtin Health Innovation Research Institute, Western Australian Biomedical Research Institute, ‡School of Biomedical Sciences, and §School of Pharmacy, Curtin University, GPO Box U1987, Perth WA 6845, Australia
| | - Ricardo L. Mancera
- Curtin Health Innovation Research Institute, Western Australian Biomedical Research Institute, ‡School of Biomedical Sciences, and §School of Pharmacy, Curtin University, GPO Box U1987, Perth WA 6845, Australia
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14
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Ravindran A, Joseph PRB, Rajarathnam K. Structural basis for differential binding of the interleukin-8 monomer and dimer to the CXCR1 N-domain: role of coupled interactions and dynamics. Biochemistry 2009; 48:8795-805. [PMID: 19681642 DOI: 10.1021/bi901194p] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Interleukin-8 (IL-8 or CXCL8) plays a critical role in orchestrating the immune response by binding and activating the receptor CXCR1 that belongs to the GPCR class. IL-8 exists as both monomers and dimers, and both bind CXCR1 but with differential affinities. It is well established that the monomer is the high-affinity ligand and that the interactions between the ligand N-loop and receptor N-domain play a critical role in determining binding affinity. In order to characterize the structural basis of differential binding of the IL-8 monomer and dimer to the CXCR1 N-domain, we analyzed binding-induced NMR chemical shift and peak intensity changes and show that they are exquisitely sensitive and can provide detailed insights into the binding process. We used three IL-8 variants, a designed monomer, a trapped disulfide-linked dimer, and WT at dimeric concentrations. NMR data for the monomer show that nonsequential residues that span the entire N-loop are involved in the binding process and that the binding is mediated by a network of extensive direct and indirect coupled interactions. Interestingly, in the case of WT, binding induces dissociation of the dimer-receptor complex to the monomer-receptor complex, and in the case of the trapped dimer, binding results in increased global conformational flexibility. Increased dynamics is evidence of unfavorable interactions, indicating that binding of the WT dimer triggers conformational changes that disrupt dimer-interface interactions, resulting in its dissociation. These results together provide evidence that binding is not a localized event but results in extensive coupled interactions within the monomer and across the dimer interface and that these interactions play a fundamental role in determining binding affinity.
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Affiliation(s)
- Aishwarya Ravindran
- Department of Biochemistry and Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, 5.142 Medical Research Building, 301 University Boulevard, The University of Texas Medical Branch, Galveston, Texas 77555, USA
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15
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Fernando H, Nagle GT, Rajarathnam K. Thermodynamic characterization of interleukin-8 monomer binding to CXCR1 receptor N-terminal domain. FEBS J 2007; 274:241-51. [PMID: 17222184 PMCID: PMC2671026 DOI: 10.1111/j.1742-4658.2006.05579.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Chemokines elicit their function by binding receptors of the G-protein-coupled receptor class, and the N-terminal domain (N-domain) of the receptor is one of the two critical ligand-binding sites. In this study, the thermodynamic basis for binding of the chemokine interleukin-8 (IL-8) to the N-domain of its receptor CXCR1 was characterized using isothermal titration calorimetry. We have shown previously that only the monomer of IL-8, and not the dimer, functions as a high-affinity ligand, so in this study we used the IL-8(1-66) deletion mutant which exists as a monomer. Calorimetry data indicate that the binding is enthalpically favored and entropically disfavored, and a negative heat capacity change indicates burial of hydrophobic residues in the complex. A characteristic feature of chemokine receptor N-domains is the large number of acidic residues, and experiments using different buffers show no net proton transfer, indicating that the CXCR1 N-domain acidic residues are not protonated in the binding process. CXCR1 N-domain peptide is unstructured in the free form but adopts a more defined structure in the bound form, and so binding is coupled to induction of the structure of the N-domain. Measurements in the presence of the osmolyte, trimethylamine N-oxide, which induces the structure of unfolded proteins, show that formation of the coupled N-domain structure involves only small DeltaH and DeltaS changes. These results together indicate that the binding is driven by packing interactions in the complex that are enthalpically favored, and are consistent with the observation that the N-domain binds in an extended form and interacts with multiple IL-8 N-loop residues over a large surface area.
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Affiliation(s)
- Harshica Fernando
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX 77555, USA
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16
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Rajagopalan L, Rajarathnam K. Structural basis of chemokine receptor function--a model for binding affinity and ligand selectivity. Biosci Rep 2006; 26:325-39. [PMID: 17024562 PMCID: PMC2671010 DOI: 10.1007/s10540-006-9025-9] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
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.
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Affiliation(s)
- Lavanya Rajagopalan
- Department of Biochemistry and Molecular Biology and Sealy Center for Structural Biology, The University of Texas Medical Branch, Galveston, TX 77555-1055, USA, e-mail:
| | - Krishna Rajarathnam
- Department of Biochemistry and Molecular Biology and Sealy Center for Structural Biology, The University of Texas Medical Branch, Galveston, TX 77555-1055, USA, e-mail:
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17
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Rajarathnam K, Prado GN, Fernando H, Clark-Lewis I, Navarro J. Probing receptor binding activity of interleukin-8 dimer using a disulfide trap. Biochemistry 2006; 45:7882-8. [PMID: 16784240 PMCID: PMC2518044 DOI: 10.1021/bi0605944] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Interleukin-8 (IL-8), a member of the chemokine superfamily, exists as both monomers and dimers, and mediates its function by binding to neutrophil CXCR1 and CXCR2 receptors that belong to the G protein-coupled receptor class. It is now well established that the monomer functions as a high-affinity ligand, but the binding affinity of the dimer remains controversial. The approximately 1000-fold difference between monomer-dimer equilibrium constant (microM) and receptor binding constant (nM) of IL-8 does not allow receptor-binding affinity measurements of the native IL-8 dimer. In this study, we overcame this roadblock by creating a "trapped" nondissociating dimer that contains a disulfide bond across the dimer interface at the 2-fold symmetry point. The NMR studies show that the structure of this trapped dimer is indistinguishable from the native dimer. The trapped dimer, compared to a trapped monomer, bound CXCR1 with approximately 70-fold and CXCR2 with approximately 20-fold lower affinities. Receptor binding involves two interactions, between the IL-8 N-loop and receptor N-domain residues, and between IL-8 N-terminal and receptor extracellular loop residues. In contrast to a trapped monomer that bound an isolated CXCR1 N-domain peptide with microM affinity, the trapped dimer failed to show any binding, indicating that dimerization predominantly perturbs the binding of only the N-loop residues. These results demonstrate that only the monomer is a high-affinity ligand for both receptors, and also provide a structural basis for the lower binding affinity of the dimer.
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Affiliation(s)
- Krishna Rajarathnam
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas 77555, USA.
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18
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Jin H, Hayes GL, Darbha NS, Meyer E, LiWang PJ. Investigation of CC and CXC chemokine quaternary state mutants. Biochem Biophys Res Commun 2005; 338:987-99. [PMID: 16256937 DOI: 10.1016/j.bbrc.2005.10.062] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2005] [Accepted: 10/07/2005] [Indexed: 11/29/2022]
Abstract
The chemokine family forms two different types of homodimer despite members sharing nearly identical folds. To study the formation of quaternary structure in this family, rational mutagenesis was employed on a representative member of each subfamily (MIP-1beta and IL-8). The variants were studied by analytical ultracentrifugation and NMR, and it was determined that formation of a folded monomer from a natural chemokine dimer is reasonably facile, while conversion between dimer types is not. Monomeric variants of MIP-1beta and IL-8 were randomly mutated and a lambda phage-based selection system was employed in a novel way to screen for dimerization. A total of 6,000,000 random mutants were screened, but no dimers were formed, suggesting again that the chemokine fold is robust and amenable to sequence variation, while the chemokine dimer is much more difficult to attain. This work represents a biophysical analysis of an array of chemokine quaternary state variants.
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Affiliation(s)
- Hongjun Jin
- Department of Biochemistry and Biophysics, Texas A&M University, TAMU 2128, College Station, TX 77843-2128, USA
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19
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David R, Machova Z, Beck-Sickinger AG. Semisynthesis and application of carboxyfluorescein-labelled biologically active human interleukin-8. Biol Chem 2004; 384:1619-30. [PMID: 14719805 DOI: 10.1515/bc.2003.180] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Human interleukin 8 (hIL-8), a neutrophil-activating and chemotactic cytokine, is known to play an important role in the pathogenesis of a large number of neutrophil-driven inflammatory diseases. This cytokine belongs to the family of CXC chemokines, mediating the response through binding to the seven-transmembrane helical G protein-coupled receptors CXCR1 and CXCR2. For the first time, we employed the expressed protein ligation (EPL) strategy to chemokine synthesis and subsequent modification. The ligation site was chosen with respect to the position of four cysteine residues within the hIL-8 sequence. Ligation with synthetic peptides that carry cysteine at their N-termini resulted in full-length hIL-8 and the specifically carboxyfluorescein-labelled analogue [K69(CF)]hIL-8(1-77). [K69(CF)]hIL-8(1-77) was fully active as shown by inhibition of cAMP production. Furthermore, this analogue was used to study receptor internalisation in human promyelotic HL60 cells that express CXCR1 and CXCR2 receptors. Binding and quenching studies were performed on HL60 membranes and suggest that the C-terminus of IL-8 is accessible to solvent in the receptor-bound state. Thus, we introduce here a powerful approach that allows the site-specific incorporation of chemical modifications into the sequence of chemokines, which opens new avenues for studying IL-8 function.
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Affiliation(s)
- Ralf David
- Institute of Biochemistry, Faculty of Biosciences, Pharmacy and Psychology, University of Leipzig, D-04103 Leipzig, Germany
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20
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Krieger E, Geretti E, Brandner B, Goger B, Wells TN, Kungl AJ. A structural and dynamic model for the interaction of interleukin-8 and glycosaminoglycans: Support from isothermal fluorescence titrations. Proteins 2004; 54:768-75. [PMID: 14997572 DOI: 10.1002/prot.10590] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Binding of interleukin-8 (IL-8) to glycosaminoglycans (GAGs) on the surface of endothelial cells is crucial for the recruitment of neutrophils to an inflammatory site. Deriving structural knowledge about this interaction from in silico docking experiments has proved difficult because of the high flexibility and the size of GAGs. Therefore, we developed a docking method that takes into account ligand and protein flexibility by running approximately 15,000 molecular dynamics simulations of the docking event with different initial orientations of the binding partners. The method was shown to successfully reproduce the residues of basic fibroblast growth factor involved in GAG binding. Docking of a heparin hexasaccharide to IL-8 gave an interaction interface involving the basic residues His18, Lys20, Arg60, Lys64, Lys67, and Arg68. By subjecting IL-8 single-site mutants, in which these amino acids were replaced by alanine, to isothermal fluorescence titrations, the affinities for heparin were determined to be wtIL-8 > IL-8(H18A) >> IL-8(R68A) > IL-8(K67A) >> IL-8(K20A) > IL-8(R60A) >> IL-8(K64A). A comparison with the binding energies calculated from the model revealed high values for wtIL-8 and the H18A mutant and significantly lower but similar energies for the remaining mutants. Connecting the two fully sulfated hexasaccharides bound to each of the two IL-8 monomers in the dimeric chemokine by an N-acetylated dodecasaccharide gave a complex structure in which the GAG molecule aligned in a parallel fashion to the N-terminal alpha-helices of IL-8 like a horseshoe. A 5-ns molecular dynamics simulation of this complex confirmed its structural stability and revealed a reorientation in both binding sites where a disaccharide became the central binding unit. Isothermal fluorescence titration experiments using differently sulfated heparin disaccharides confirmed that a single disaccharide can indeed bind IL-8 with high affinity.
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Affiliation(s)
- Elmar Krieger
- Centre for Molecular and Biomolecular Informatics, Nijmegen, The Netherlands
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21
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Wilce JA, Love SG, Richardson SJ, Alewood PF, Craik DJ. Synthesis of an Analog of the Thyroid Hormone-binding Protein Transthyretin via Regioselective Chemical Ligation. J Biol Chem 2001; 276:25997-6003. [PMID: 11352912 DOI: 10.1074/jbc.m101228200] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Transthyretin is an essential protein responsible for the transport of thyroid hormones and retinol in human serum and is also implicated in the amyloid diseases familial amyloidotic polyneuropathy and senile systemic amyloidosis. Its folding properties and stabilization by ligands are of current interest due to their importance in understanding and combating these diseases. Here we report the solid phase synthesis of the monomeric unit of a transthyretin analog (equivalent to 127 amino acids) using t-Boc chemistry and peptide ligation and its folding to form a functional 54-kDa tetramer. The monomeric unit of the protein was chemically synthesized in three parts (positions 1--51, 54--99, and 102--127) and ligated using a chemoselective thioether ligation chemistry. The synthetic protein was folded and assembled to a tetrameric structure in the presence of transthyretin's native ligand, thyroxine, as shown by gel filtration chromatography, native gel electrophoresis, transthyretin antibody recognition, and thyroid hormone binding. Other folding products included a high molecular weight aggregate as well as a transient dimeric species. This represents one of the largest macromolecules chemically synthesized to date and demonstrates the potential of protein chemical synthesis for investigations of protein-ligand interactions.
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Affiliation(s)
- J A Wilce
- Department of Biochemistry/Chemistry, University of Western Australia, Nedlands Western Australia 6907, Australia
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22
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Stoeckelhuber M, Dobner P, Baumgartner P, Ehlert J, Brandt E, Mentele R, Adam D, Engelmann B. Stimulation of cellular sphingomyelin import by the chemokine connective tissue-activating peptide III. J Biol Chem 2000; 275:37365-72. [PMID: 10956644 DOI: 10.1074/jbc.m003709200] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The selective import of phospholipids into cells could be mediated by proteins secreted from the cells into the extracellular compartment. We observed that the supernatants obtained from suspensions of thrombin-activated platelets stimulated the exchange of pyrene (py)-labeled sphingomyelin between lipid vesicles in vitro. The proteins with sphingomyelin transfer activity were purified and identified as the chemokine connective tissue-activating peptide III (CTAP-III) and platelet basic protein. Isolated CTAP-III stimulated the exchange of py-sphingomyelin between lipid vesicles but did not affect the translocations of py-labeled phosphatidylcholine and phosphatidylethanolamine. CTAP-III rapidly increased the transfer of py-sphingomyelin from low density lipoproteins into peripheral blood lymphocytes, other immune cells, and fibroblasts. In the presence of heparin, CTAP-III was unable to insert sphingomyelin into the peripheral blood lymphocytes. The activation energy of the py-sphingomyelin transfer suggested that the translocation proceeded entirely in a hydrophobic environment. [(3)H]Sphingomyelin transferred to the cells by CTAP-III was hydrolyzed to [(3)H]ceramide and [(3)H]sphingosine after activation with tumor necrosis factor alpha. The generation of the [(3)H]sphingolipid messengers was catalyzed by acid sphingomyelinase. Our results identify CTAP-III as the first mediator of the selective (endocytosis-independent) cellular import of sphingomyelin allowing the paracrine modulation of the sphingolipid signaling.
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Affiliation(s)
- M Stoeckelhuber
- Physiologisches Institut der Universität München, Schillerstrasse 44, 80336 München, Germany
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23
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Crump MP, Rajarathnam K, Kim KS, Clark-Lewis I, Sykes BD. Solution structure of eotaxin, a chemokine that selectively recruits eosinophils in allergic inflammation. J Biol Chem 1998; 273:22471-9. [PMID: 9712872 DOI: 10.1074/jbc.273.35.22471] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The solution structure of the CCR3-specific chemokine, eotaxin, has been determined by NMR spectroscopy. The quaternary structure of eotaxin was investigated by ultracentrifugation and NMR, and it was found to be in equilibrium between monomer and dimer under a wide range of conditions. At pH </= 5 and low ionic strength, eotaxin was found to be predominantly a monomer. The three-dimensional structure of the eotaxin monomer solved at pH 5.0 revealed that it has a typical chemokine fold, which includes a 3-stranded beta-sheet and an overlying alpha-helix. Except for the N-terminal residues (residues 1-8), the core of the protein is well defined. The eotaxin structure is compared with the chemokines regulated upon activation, normal T-cell expressed and secreted (RANTES) and monocyte chemoattractant protein-1 (MCP-1); eotaxin binds only CC chemokine receptor CCR3, whereas RANTES binds many receptors including CCR3, and MCP-1 binds a distinct receptor, CCR2. The RMSD of the eotaxin ensemble of structures with the RANTES average minimized monomeric subunit is 5.52 +/- 0.87 A over all backbone atoms and 1.14 +/- 0.09 A over backbone atoms of residues 11-28 and 34-65. The most important difference between the structures is in the N-terminal residues that are unstructured in eotaxin but structured in RANTES and MCP-1. Several residues in the loop region of RANTES show similar packing in eotaxin (residues 11-17). As the N-terminal and loop regions have been shown to be critical for receptor binding and signaling, this structure will be useful for determining the basis for CCR3 selectivity of the eotaxin.
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Affiliation(s)
- M P Crump
- Protein Engineering Network of Centres of Excellence (PENCE) and Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
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Abstract
Chemical protein synthesis is a field in transition. Previously, the synthetic accomplishment itself was the major focus of work in this field. Increasingly, chemical synthesis is now being applied to understanding how biological function originates in the structure of the protein molecule. A novel approach--'chemical ligation', which is the chemoselective reaction of unprotected peptide segments in water at pH7--has made the total synthesis of proteins a robust and practical route to the study of structure-function relationships. For certain protein families, chemical protein synthesis is the most effective way to obtain functional proteins direct from genome sequence data.
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Affiliation(s)
- J Wilken
- Gryphon Sciences, South San Francisco, California, USA
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