Conformational analysis and docking study of potent factor XIIIa inhibitors having a cyclopropenone ring.

A conformational analysis and docking study of potent factor XIIIa inhibitors having a cyclopropenone ring were carried out in an attempt to obtain structural insight into the inhibition mechanism. First, stable conformers of the inhibitors alone were obtained from the conformational analysis by systematic search and molecular dynamics. Next, a binding form model of factor XIIIa was built based on an X-ray crystal structure of the enzyme. Finally, the docking study of the inhibitors into the model's binding site was performed. From the resulting stable complex structures, it was found that the cyclopropenone ring fits the active site located at the base of the binding cavity with high complementarity. The carbonyl oxygen of the cyclopropenone ring formed a hydrogen bond to the indole NH group of Trp279 and the terminal carbon atom of the reactive C=C double bond was in close proximity to the sulfur atom of the catalytic residue, Cys314. This binding mode suggests a possible inhibition mechanism, whereby the cysteine residue reacts with the cyclopropenone ring of the inhibitor, forming an enzyme-ligand adduct. In addition, the higher interaction energies between factor XIIIa and the inhibitors alluded to the probable binding sites of the ligand side chain.

Scyphostatin, a neutral sphingomyelinase inhibitor from a discomycete, Trichopeziza mollissima: taxonomy of the producing organism, fermentation, isolation, and physico-chemical properties.

We performed experiments to screen for neutral sphingomyelinase inhibitors using rat brain microsomes as an enzyme source. Among more than 10,000 microbial extracts tested, a mycelial extract of Trichopeziza mollissima SANK 13892 exhibited potent inhibitory activity. The active compound, scyphostatin, was purified by a series of chromatographies. Scyphostatin inhibited the enzyme with an IC50 value of 1.0 microM.

Biological activities of scyphostatin, a neutral sphingomyelinase inhibitor from a discomycete, Trichopeziza mollissima.

Scyphostatin is a specific inhibitor for mammalian neutral magnesium-dependent sphingomyelinase with a fifty percent inhibition concentration (IC50) value of 1.0 microM. When used to inhibit lysosomal acid sphingomyelinase, an approximately 50-fold greater concentration is required. In human peripheral monocytes, the compound inhibits bacterial lipopolysaccharide (LPS)-induced prostaglandin E2 production and LPS-induced interleukin-1beta production with IC50 values of 0.8 microM and 0.1 microM, respectively. In rat, p.o. administration of the compound has also been shown to inhibit carrageenin-induced paw edema. Thus, it is hoped that utility of scyphostatin as a pharmacological tool will contribute to our understanding of the role of ceramide in the cellular inflammation process.