The Chemical Basis of Serine Palmitoyltransferase Inhibition by Myriocin

Abstract

Sphingolipids (SLs) are essential components of cellular membranes formed from the condensation of L-serine and a long-chain acyl thioester. This first step is catalyzed by the pyridoxal-5'-phosphate (PLP)-dependent enzyme serine palmitoyltransferase (SPT) which is a promising therapeutic target. The fungal natural product myriocin is a potent inhibitor of SPT and is widely used to block SL biosynthesis despite a lack of a detailed understanding of its molecular mechanism. By combining spectroscopy, mass spectrometry, X-ray crystallography, and kinetics, we have characterized the molecular details of SPT inhibition by myriocin. Myriocin initially forms an external aldimine with PLP at the active site, and a structure of the resulting co-complex explains its nanomolar affinity for the enzyme. This co-complex then catalytically degrades via an unexpected 'retro-aldol-like' cleavage mechanism to a C18 aldehyde which in turn acts as a suicide inhibitor of SPT by covalent modification of the essential catalytic lysine. This surprising dual mechanism of inhibition rationalizes the extraordinary potency and longevity of myriocin inhibition.

The Crucial Role of C18-Cer in Fat-Induced Skeletal Muscle Insulin Resistance

“…Despite Myr treatment SPT expression was equal in both HFD and HFD/Myr animals. Myriocin acts as suicide inhibitor of SPT by covalent modification of essential catalytic serine, thus does not affect SPT expression but completely bocks its enzymatic activity at low nanomolar concentrations [54].…”

Sphingolipid De Novo Biosynthesis: A Rheostat of Cardiovascular Homeostasis

“…The role of the Orm proteins in regulation of SPT was first reported in an elegant study by Breslow and colleagues who showed that the Orms inhibit SPT when the cells have sufficient levels of SL [20], and the lack of Orms significantly increased he activity of SPT of six folds. When sphingolipid synthesis is disrupted by myriocin, an inhibitor of SPT activity [21], the Orms are phosphorylated at multiple sites and the inhibitory brake on SPT is relieved. As predicted, deletion or phosphomimicking mutations in the ORMs cause hyperactivation of SPT [20].…”

Determination of the serine palmitoyl transferase inhibitor myriocin by electrospray and Q‐trap mass spectrometry

“…Then, the co-complex degrades via an unexpected 'retro-aldol-like' cleavage mechanism to a long chain aldehyde which, in turn, irreversibly reacts with the key catalytic residue Lys265, acting as a "suicide inhibitor" of SPT (Wadsworth et al, 2013).…”