The catalytic formation of leukotriene C4: a critical step in inflammatory processes

Abstract

Leukotrienes (LT) are a family of drug-like molecules involved in the pathobiology of bronchial asthma and are responsible for smooth muscle contraction. Leukotriene C₄ synthase (LTC₄S) is a nuclear-membrane enzyme responsible for the conjugation of leukotriene A₄ (LTA₄) to glutathione to form LTC₄, a cysteinyl leukotriene. In this study, the mechanism of LTA₄ binding by LTC₄S has been computationally examined. More specifically, docking and molecular dynamics simulations were used to gain insight into the substrate-bound active site. These studies identified two possible orientations for bound LTA₄: ‘tail-to-head’ and ‘head-to-tail’. An ONIOM(QM/MM) approach was then used to elucidate the mechanism by which glutathione may add to LTA₄. In particular, the thiolate of glutathione acts as a nucleophile attacking C₆ of LTA₄ forming a S–C₆ bond. Concomitantly, a proton is transferred from the guanidinium of Arg₃₁ to the epoxide ring oxygen. This results in opening of the epoxide ring and stabilization of the LTC₄ product complex. Within the present computational methodology the ‘tail-to-head’ orientation appears to be the most likely substrate orientation.