Fig. 6: Proposed double-displacement (ping-pong) mechanism of CerSs.
From: Structural basis of the mechanism and inhibition of a human ceramide synthase
Initially, the acyl-CoA substrate binds with the acyl chain buried deep within the central tunnel and the CoA moiety sitting near the cytoplasmic entrance to the central cavity. In the first step, the nucleophilic attack of His211 on the acyl-CoA thioester carbonyl results in thioester cleavage, covalent acyl–imidazole intermediate formation and release of CoA. Subsequently, the long-chain sphingoid base substrate binds with its hydrocarbon chain interacting with the hydrophobic face of the central cavity and its amino alcohol moiety sitting in the side pocket in the active site. In the second step of the reaction, the primary amine of the long-chain base attacks the acyl–imidazole intermediate, leading to covalent intermediate breakdown and formation of the final N-acyl sphingoid base (ceramide) product.
