Abstract
CXCL7, a chemokine highly expressed in platelets, orchestrates neutrophil recruitment during thrombosis and related pathophysiological processes by interacting with CXCR2 receptor and sulfated glycosaminoglycans (GAG). CXCL7 exists as monomers and dimers, and dimerization (~50 μM) and CXCR2 binding (~10 nM) constants indicate that CXCL7 is a potent agonist as a monomer. Currently, nothing is known regarding the structural basis by which receptor and GAG interactions mediate CXCL7 function. Using solution nuclear magnetic resonance (NMR) spectroscopy, we characterized the binding of CXCL7 monomer to the CXCR2 N-terminal domain (CXCR2Nd) that constitutes a critical docking site and to GAG heparin. We found that CXCR2Nd binds a hydrophobic groove and that ionic interactions also play a role in mediating binding. Heparin binds a set of contiguous basic residues indicating a prominent role for ionic interactions. Modeling studies reveal that the binding interface is dynamic and that GAG adopts different binding geometries. Most importantly, several residues involved in GAG binding are also involved in receptor interactions, suggesting that GAG-bound monomer cannot activate the receptor. Further, this is the first study that describes the structural basis of receptor and GAG interactions of a native monomer of the neutrophil-activating chemokine family.
Highlights
Chemokines, a large family of signaling proteins, mediate diverse biological functions, including inflammation, development and tissue repair [1,2,3]
The sulfated as a critical ligand and servesinterface as a representative and well-studied, bindingthis interface is inferred from binding-induced shifts from heteronuclear end, we first assigned the chemicalchemical shifts of the obtained native monomer that are essential single quantum coherence (HSQC) titrations of an unlabeled ligand to a 15N-labeled protein
Knowledge of the native CXCL7 monomer chemical shifts is essential to describe the molecular basis of receptor and GAG interactions
Summary
Chemokines, a large family of signaling proteins, mediate diverse biological functions, including inflammation, development and tissue repair [1,2,3]. Chemokines mediate their function by activating seven transmembrane G-protein coupled receptors (GPCRs) and binding sulfated glycosaminoglycans (GAGs) that regulate receptor function [4,5,6]. Another key feature of chemokines is their ability to reversibly exist as monomers and dimers and sometimes as higher order oligomers. CXCL7 belongs to a subset of CXC neutrophil-activating chemokines (NACs) that are characterized by an
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