title: Alternative C-terminal helix orientation alters chemokine function: structure of the anti-angiogenic chemokine, CXCL4L1.
abstract: BACKGROUND
  CXCL4L1 is a highly potent anti-angiogenic and anti-tumor chemokine, and its structural information is unknown.
  
  
  RESULTS
  CXCL4L1 x-ray structure is determined, and it reveals a previously unrecognized chemokine structure adopting a novel C-terminal helix conformation.
  
  
  CONCLUSIONS
  The alternative helix conformation enhances the anti-angiogenic activity of CXCL4L1 by reducing the glycosaminoglycan binding ability.
  
  
  CONCLUSIONS
  Chemokine C-terminal helix orientation is critical in regulating their functions. Chemokines, a subfamily of cytokines, are small, secreted proteins that mediate a variety of biological processes. Various chemokines adopt remarkable conserved tertiary structure comprising an anti-parallel β-sheet core domain followed by a C-terminal helix that packs onto the β-sheet. The conserved structural feature has been considered critical for chemokine function, including binding to cell surface receptor. The recently isolated variant, CXCL4L1, is a homologue of CXCL4 chemokine (or platelet factor 4) with potent anti-angiogenic activity and differed only in three amino acid residues of P58L, K66E, and L67H. In this study we show by x-ray structural determination that CXCL4L1 adopts a previously unrecognized structure at its C terminus. The orientation of the C-terminal helix protrudes into the aqueous space to expose the entire helix. The alternative helix orientation modifies the overall chemokine shape and surface properties. The L67H mutation is mainly responsible for the swing-out effect of the helix, whereas mutations of P58L and K66E only act secondarily. This is the first observation that reports an open conformation of the C-terminal helix in a chemokine. This change leads to a decrease of its glycosaminoglycan binding properties and to an enhancement of its anti-angiogenic and anti-tumor effects. This unique structure is recent in evolution and has allowed CXCL4L1 to gain novel functional properties.
authors.affiliation: Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu 30013, Taiwan.
authors.forename: Je-Hung
authors.initials: JH
authors.lastname: Kuo
authors.forename: Ya-Ping
authors.initials: YP
authors.lastname: Chen
authors.forename: Jai-Shin
authors.initials: JS
authors.lastname: Liu
authors.forename: Alexandre
authors.initials: A
authors.lastname: Dubrac
authors.forename: Cathy
authors.initials: C
authors.lastname: Quemener
authors.forename: Hervé
authors.initials: H
authors.lastname: Prats
authors.forename: Andreas
authors.initials: A
authors.lastname: Bikfalvi
authors.forename: Wen-guey
authors.initials: WG
authors.lastname: Wu
authors.forename: Shih-Che
authors.initials: SC
authors.lastname: Sue
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D042501:Angiogenic Proteins / Q000737:chemistry; D018360:Crystallography, X-Ray; D003553:Cystine / Q000737:chemistry; D004229:Dithiothreitol / Q000737:chemistry; D006493:Heparin / Q000737:chemistry; D006801:Humans; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D010978:Platelet Factor 4 / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D011485:Protein Binding; D017510:Protein Folding; D054730:Protein Interaction Domains and Motifs; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D019163:Reducing Agents / Q000737:chemistry
chemical_list: D042501:Angiogenic Proteins; C064936:PF4V1 protein, human; D019163:Reducing Agents; D010978:Platelet Factor 4; D003553:Cystine; D006493:Heparin; D004229:Dithiothreitol
keywords: Angiogenesis; CXCL4L1; Chemokines; Heparin; Platelet Factor 4; Platelets; X-ray Crystallography
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