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Open Biol. 2017 Oct;7(10). pii: 170133. doi: 10.1098/rsob.170133.

Solution structure of CXCL13 and heparan sulfate binding show that GAG binding site and cellular signalling rely on distinct domains.

Author information

1
University of Grenoble Alpes, CNRS, CEA, IBS, 38000 Grenoble, France.
2
Institut Pasteur, INSERM U1108, Paris, France.
3
Institute for Structural Biology, Drug Discovery and Development, Virginia Commonwealth University, Richmond, VA, USA.
4
Department of Medicinal Chemistry, Virginia Commonwealth University, Richmond, VA, USA.
5
Institut Pasteur, Unité de Chimie des Biomolécules, UMR CNRS 3523, Paris, France.
6
University of Grenoble Alpes, CNRS, CEA, IBS, 38000 Grenoble, France hugues.lortat-jacob@ibs.fr.

Abstract

Chemokines promote directional cell migration through binding to G-protein-coupled receptors, and as such are involved in a large array of developmental, homeostatic and pathological processes. They also interact with heparan sulfate (HS), the functional consequences of which depend on the respective location of the receptor- and the HS-binding sites, a detail that remains elusive for most chemokines. Here, to set up a biochemical framework to investigate how HS can regulate CXCL13 activity, we solved the solution structure of CXCL13. We showed that it comprises an unusually long and disordered C-terminal domain, appended to a classical chemokine-like structure. Using three independent experimental approaches, we found that it displays a unique association mode to HS, involving two clusters located in the α-helix and the C-terminal domain. Computational approaches were used to analyse the HS sequences preferentially recognized by the protein and gain atomic-level understanding of the CXCL13 dimerization induced upon HS binding. Starting with four sets of 254 HS tetrasaccharides, we identified 25 sequences that bind to CXCL13 monomer, among which a single one bound to CXCL13 dimer with high consistency. Importantly, we found that CXCL13 can be functionally presented to its receptor in a HS-bound form, suggesting that it can promote adhesion-dependent cell migration. Consistently, we designed CXCL13 mutations that preclude interaction with HS without affecting CXCR5-dependent cell signalling, opening the possibility to unambiguously demonstrate the role of HS in the biological function of this chemokine.

KEYWORDS:

CXCL13; chemokine; glycosaminoglycan; heparan sulfate binding site; heparan sulfate sequence

PMID:
29070611
PMCID:
PMC5666081
DOI:
10.1098/rsob.170133
[Indexed for MEDLINE]
Free PMC Article

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