title: Structural basis for synthesis of inflammatory mediators by human leukotriene C4 synthase.
abstract: Cysteinyl leukotrienes are key mediators in inflammation and have an important role in acute and chronic inflammatory diseases of the cardiovascular and respiratory systems, in particular bronchial asthma. In the biosynthesis of cysteinyl leukotrienes, conversion of arachidonic acid forms the unstable epoxide leukotriene A4 (LTA4). This intermediate is conjugated with glutathione (GSH) to produce leukotriene C4 (LTC4) in a reaction catalysed by LTC4 synthase: this reaction is the key step in cysteinyl leukotriene formation. Here we present the crystal structure of the human LTC4 synthase in its apo and GSH-complexed forms to 2.00 and 2.15 A resolution, respectively. The structure reveals a homotrimer, where each monomer is composed of four transmembrane segments. The structure of the enzyme in complex with substrate reveals that the active site enforces a horseshoe-shaped conformation on GSH, and effectively positions the thiol group for activation by a nearby arginine at the membrane-enzyme interface. In addition, the structure provides a model for how the omega-end of the lipophilic co-substrate is pinned at one end of a hydrophobic cleft, providing a molecular 'ruler' to align the reactive epoxide at the thiol of glutathione. This provides new structural insights into the mechanism of LTC4 formation, and also suggests that the observed binding and activation of GSH might be common for a family of homologous proteins important for inflammatory and detoxification responses.
authors.affiliation: Division of Biophysics, Karolinska Institutet, 17177 Stockholm, Sweden.
authors.forename: Daniel
authors.initials: D
authors.lastname: Martinez Molina
authors.forename: Anders
authors.initials: A
authors.lastname: Wetterholm
authors.forename: Andreas
authors.initials: A
authors.lastname: Kohl
authors.forename: Andrew A
authors.initials: AA
authors.lastname: McCarthy
authors.forename: Damian
authors.initials: D
authors.lastname: Niegowski
authors.forename: Eva
authors.initials: E
authors.lastname: Ohlson
authors.forename: Tove
authors.initials: T
authors.lastname: Hammarberg
authors.forename: Said
authors.initials: S
authors.lastname: Eshaghi
authors.forename: Jesper Z
authors.initials: JZ
authors.lastname: Haeggström
authors.forename: Pär
authors.initials: P
authors.lastname: Nordlund
mesh_terms: D001051:Apoenzymes / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D005978:Glutathione / Q000737:chemistry / Q000378:metabolism; D005982:Glutathione Transferase / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D018836:Inflammation Mediators / Q000378:metabolism*; D050356:Lipid Metabolism; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D001051:Apoenzymes; D018836:Inflammation Mediators; D005982:Glutathione Transferase; C041116:leukotriene-C4 synthase; D005978:Glutathione