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The Anti-inflammatory Protein TSG-6 Regulates Chemokine Function by Inhibiting Chemokine/Glycosaminoglycan Interactions.

Dyer DP, Salanga CL, Johns SC, Valdambrini E, Fuster MM, Milner CM, Day AJ, Handel TM - J. Biol. Chem. (2016)

Bottom Line: We also show that the Link_TSG6-binding sites on chemokines overlap with chemokine GAG-binding sites, and that the affinities of Link_TSG6 for these chemokines (KD values 1-85 nm) broadly correlate with chemokine-GAG affinities.Link_TSG6 also inhibits chemokine presentation on endothelial cells not only through a direct interaction with chemokines but also by binding and therefore masking the availability of GAGs.Along with previous work, these findings suggest that TSG-6 functions as a pluripotent regulator of chemokines by modulating chemokine/GAG interactions, which may be a major mechanism by which TSG-6 produces its anti-inflammatory effects in vivo.

View Article: PubMed Central - PubMed

Affiliation: From the Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92093-0684, the Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8TA, Scotland, United Kingdom.

No MeSH data available.


Related in: MedlinePlus

Interaction sites for CS/HA, heparin, and potential binding sites for chemokines on Link_TSG6. Structure of a Link_TSG6 complex with CS (Protein Data Bank code 2N40) is shown, where Link_TSG6 is represented as a surface mesh, and CS is shown as a space-filling model. The green surface of Link_TSG6 highlights the aromatics that define the CS/HA-binding site (9, 84) and could provide a binding site for chemokines through their GAG-binding epitopes. The blue surface highlights the basic residues that define the heparin-binding site as determined previously (75), which is not compatible with chemokine binding. The red surface highlights Glu residues that could provide a binding site for chemokines through their GAG-binding epitopes.
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Figure 12: Interaction sites for CS/HA, heparin, and potential binding sites for chemokines on Link_TSG6. Structure of a Link_TSG6 complex with CS (Protein Data Bank code 2N40) is shown, where Link_TSG6 is represented as a surface mesh, and CS is shown as a space-filling model. The green surface of Link_TSG6 highlights the aromatics that define the CS/HA-binding site (9, 84) and could provide a binding site for chemokines through their GAG-binding epitopes. The blue surface highlights the basic residues that define the heparin-binding site as determined previously (75), which is not compatible with chemokine binding. The red surface highlights Glu residues that could provide a binding site for chemokines through their GAG-binding epitopes.

Mentions: In this study, we showed that TSG-6 binds to all chemokines tested through their GAG-binding sites. The high resolution molecular details of how it does so remains an important question because chemokines are overall basic proteins, but TSG-6 is basic as well (pI ∼9.48 (84)). Previously, it was shown that a mutant of Link_TSG6 (Link_TSG6_T), with reduced capacity to bind heparin (27), was still capable of binding to CXCL8 and inhibiting both its interaction with GAGs and transendothelial cell migration toward CXCL8 (30). Similarly, in this study, we showed that this Link_TSG6 mutant could inhibit CXCL11, CCL2, CCL7, and CCL19 interactions with heparin. These findings suggest that the heparin-binding site on Link_TSG6 (Fig. 12) does not overlap with its binding site for CXCL8 and the above chemokines, which may very well be the case for other chemokines. This would not be surprising because the heparin-binding surface of Link_TSG6 is composed of basic residues, making it incompatible with chemokine GAG-binding sites, which are also defined by clusters of Arg, Lys, and His (86, 87). Instead, the interaction with the GAG-binding domains of chemokines may be mediated by negatively charged amino acids in Link_TSG6 (Fig. 12). Alternatively, as the binding site on Link_TSG6 for HA/CS is non-overlapping with heparin and enriched with aromatic residues, it is possible that it could provide a binding site for chemokines (Fig. 12). In this case, favorable cation/π interactions (88, 89) between the Link_TSG6 aromatic residues and Lys/Arg residues in the chemokine GAG-binding epitopes could contribute to complex formation. Identification of the chemokine-binding sites on TSG-6 will be the subject of future studies.


The Anti-inflammatory Protein TSG-6 Regulates Chemokine Function by Inhibiting Chemokine/Glycosaminoglycan Interactions.

Dyer DP, Salanga CL, Johns SC, Valdambrini E, Fuster MM, Milner CM, Day AJ, Handel TM - J. Biol. Chem. (2016)

Interaction sites for CS/HA, heparin, and potential binding sites for chemokines on Link_TSG6. Structure of a Link_TSG6 complex with CS (Protein Data Bank code 2N40) is shown, where Link_TSG6 is represented as a surface mesh, and CS is shown as a space-filling model. The green surface of Link_TSG6 highlights the aromatics that define the CS/HA-binding site (9, 84) and could provide a binding site for chemokines through their GAG-binding epitopes. The blue surface highlights the basic residues that define the heparin-binding site as determined previously (75), which is not compatible with chemokine binding. The red surface highlights Glu residues that could provide a binding site for chemokines through their GAG-binding epitopes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4933465&req=5

Figure 12: Interaction sites for CS/HA, heparin, and potential binding sites for chemokines on Link_TSG6. Structure of a Link_TSG6 complex with CS (Protein Data Bank code 2N40) is shown, where Link_TSG6 is represented as a surface mesh, and CS is shown as a space-filling model. The green surface of Link_TSG6 highlights the aromatics that define the CS/HA-binding site (9, 84) and could provide a binding site for chemokines through their GAG-binding epitopes. The blue surface highlights the basic residues that define the heparin-binding site as determined previously (75), which is not compatible with chemokine binding. The red surface highlights Glu residues that could provide a binding site for chemokines through their GAG-binding epitopes.
Mentions: In this study, we showed that TSG-6 binds to all chemokines tested through their GAG-binding sites. The high resolution molecular details of how it does so remains an important question because chemokines are overall basic proteins, but TSG-6 is basic as well (pI ∼9.48 (84)). Previously, it was shown that a mutant of Link_TSG6 (Link_TSG6_T), with reduced capacity to bind heparin (27), was still capable of binding to CXCL8 and inhibiting both its interaction with GAGs and transendothelial cell migration toward CXCL8 (30). Similarly, in this study, we showed that this Link_TSG6 mutant could inhibit CXCL11, CCL2, CCL7, and CCL19 interactions with heparin. These findings suggest that the heparin-binding site on Link_TSG6 (Fig. 12) does not overlap with its binding site for CXCL8 and the above chemokines, which may very well be the case for other chemokines. This would not be surprising because the heparin-binding surface of Link_TSG6 is composed of basic residues, making it incompatible with chemokine GAG-binding sites, which are also defined by clusters of Arg, Lys, and His (86, 87). Instead, the interaction with the GAG-binding domains of chemokines may be mediated by negatively charged amino acids in Link_TSG6 (Fig. 12). Alternatively, as the binding site on Link_TSG6 for HA/CS is non-overlapping with heparin and enriched with aromatic residues, it is possible that it could provide a binding site for chemokines (Fig. 12). In this case, favorable cation/π interactions (88, 89) between the Link_TSG6 aromatic residues and Lys/Arg residues in the chemokine GAG-binding epitopes could contribute to complex formation. Identification of the chemokine-binding sites on TSG-6 will be the subject of future studies.

Bottom Line: We also show that the Link_TSG6-binding sites on chemokines overlap with chemokine GAG-binding sites, and that the affinities of Link_TSG6 for these chemokines (KD values 1-85 nm) broadly correlate with chemokine-GAG affinities.Link_TSG6 also inhibits chemokine presentation on endothelial cells not only through a direct interaction with chemokines but also by binding and therefore masking the availability of GAGs.Along with previous work, these findings suggest that TSG-6 functions as a pluripotent regulator of chemokines by modulating chemokine/GAG interactions, which may be a major mechanism by which TSG-6 produces its anti-inflammatory effects in vivo.

View Article: PubMed Central - PubMed

Affiliation: From the Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92093-0684, the Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8TA, Scotland, United Kingdom.

No MeSH data available.


Related in: MedlinePlus