title: Chemokine CXCL7 Heterodimers: Structural Insights, CXCR2 Receptor Function, and Glycosaminoglycan Interactions.
abstract: Chemokines mediate diverse fundamental biological processes, including combating infection. Multiple chemokines are expressed at the site of infection; thus chemokine synergy by heterodimer formation may play a role in determining function. Chemokine function involves interactions with G-protein-coupled receptors and sulfated glycosaminoglycans (GAG). However, very little is known regarding heterodimer structural features and receptor and GAG interactions. Solution nuclear magnetic resonance (NMR) and molecular dynamics characterization of platelet-derived chemokine CXCL7 heterodimerization with chemokines CXCL1, CXCL4, and CXCL8 indicated that packing interactions promote CXCL7-CXCL1 and CXCL7-CXCL4 heterodimers, and electrostatic repulsive interactions disfavor the CXCL7-CXCL8 heterodimer. As characterizing the native heterodimer is challenging due to interference from monomers and homodimers, we engineered a "trapped" disulfide-linked CXCL7-CXCL1 heterodimer. NMR and modeling studies indicated that GAG heparin binding to the heterodimer is distinctly different from the CXCL7 monomer and that the GAG-bound heterodimer is unlikely to bind the receptor. Interestingly, the trapped heterodimer was highly active in a Ca2+release assay. These data collectively suggest that GAG interactions play a prominent role in determining heterodimer function in vivo. Further, this study provides proof-of-concept that the disulfide trapping strategy can serve as a valuable tool for characterizing the structural and functional features of a chemokine heterodimer.
authors.affiliation: Department of Biochemistry and Molecular Biology, and Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555, USA. aj3brown@utmb.edu.
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Brown
authors.affiliation: Department of Biochemistry and Molecular Biology, and Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555, USA. pbjoseph@utmb.edu.
authors.forename: Prem Raj B
authors.initials: PR
authors.lastname: Joseph
authors.affiliation: Department of Biochemistry and Molecular Biology, and Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555, USA. kisawant@utmb.edu.
authors.forename: Kirti V
authors.initials: KV
authors.lastname: Sawant
authors.affiliation: Department of Biochemistry and Molecular Biology, and Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555, USA. krrajara@utmb.edu.
authors.forename: Krishna
authors.initials: K
authors.lastname: Rajarathnam
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D002118:Calcium / Q000378:metabolism; D054360:Chemokine CXCL1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006025:Glycosaminoglycans / Q000737:chemistry* / Q000378:metabolism; D018922:HL-60 Cells; D006493:Heparin / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D016209:Interleukin-8 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D056004:Molecular Dynamics Simulation; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D010978:Platelet Factor 4 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D000072417:Protein Domains; D055503:Protein Multimerization; D017386:Sequence Homology, Amino Acid; D001620:beta-Thromboglobulin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: C475829:CXCL1 protein, human; D054360:Chemokine CXCL1; D006025:Glycosaminoglycans; D016209:Interleukin-8; D009844:Oligosaccharides; C061615:PPBP protein, human; D001620:beta-Thromboglobulin; D010978:Platelet Factor 4; D006493:Heparin; D002118:Calcium
keywords: CXCL7; CXCR2; NMR; chemokine; glycosaminoglycan; heparin; heterodimer