Crystal Structures of Leukotriene C4 Synthase in Complex with Product Analogs

Background: Leukotriene (LT) C-4 synthase (LTC4S) is a membrane protein catalyzing the formation of pathogenic mediators of asthma. Results: Crystal structures of complexes of WT and mutated LTC4S with three product analogs. Conclusion: Evidence for the binding mode of LTA(4) and LTC4 at the active site of LTC4S and a mechanistic model. Significance: New insights into the molecular mechanism of LTC4S. Leukotriene (LT) C-4 synthase (LTC4S) catalyzes the conjugation of the fatty acid LTA(4) with the tripeptide GSH to produce LTC4, the parent compound of the cysteinyl leukotrienes, important mediators of asthma. Here we mutated Trp-116 in human LTC4S, a residue proposed to play a key role in substrate binding, into an Ala or Phe. Biochemical and structural characterization of these mutants along with crystal structures of the wild type and mutated enzymes in complex with three product analogs, viz. S-hexyl-, 4-phenyl-butyl-, and 2-hydroxy-4-phenyl-butyl-glutathione, provide new insights to binding of substrates and product, identify a new conformation of the GSH moiety at the active site, and suggest a route for product release, aided by Trp-116.