Over the past years, family 18 chitinases have been validated as potential targets for the design of drugs against human pathogens that contain or interact with chitin during their normal life cycles. Thus far, only one potent chitinase inhibitor has been described in detail, the pseudotrisaccharide allosamidin. Recently, however, two potent natural-product cyclopentapeptide chitinase inhibitors, argifin and argadin, were reported. Here, we describe highresolution crystal structures that reveal the details of the interactions of these cyclopeptides with a family 18 chitinase. The structures are examples of complexes of a carbohydrateprocessing enzyme with high-affinity peptide-based inhibitors and show in detail how the peptide backbone and side chains mimic the interactions of the enzyme with chitooligosaccharides. Together with enzymological characterization, the structures explain why argadin shows an order of magnitude stronger inhibition than allosamidin, whereas argifin shows weaker inhibition. The peptides bind to the chitinase in remarkably different ways, which may explain the differences in inhibition constants. The two complexes provide a basis for structure-based design of potent chitinase inhibitors, accessible by standard peptide chemistry.

A new chitinase inhibitor, designated as argadin (1), was isolated from the cultured broth of a fungal strain FO-7314. The strain was identified as Clonostachys sp. from the morphological characteristics. Argadin was purified from the cultured mycelium by a combination of cation exchange, adsorption and gel filtration chromatographic methods. The structure of argadin was elucidated as cyclo(Nomega-acetyl-L-arginyl-D-prolyl-homoseryl-histidyl-L- 2-aminoadipyl) in which homoseryl gamma-methylene bonded to histidyl alpha-amino residue. The IC50 value of argadin against Lucilia cuprina (blowfly) chitinase was 150 nM at 37 degrees C and 3.4 nM at 20 degrees C. Argadin arrested the moult of cockroach larvae upon injection into the ventral abdominal part.

A new chitinase inhibitor, named argifin, was isolated from the cultured broth of a fungal strain FTD-0668. The strain was identified as Gliocladium sp. from morphological

Newazaphilones named isochromophilones III~VI were isolated from the culture broth of Penicillium multicolor FO-3216 as inhibitors of acyl-CoA : cholesterol acyltransferase (ACAT). Their structures were elucidated by NMR and other spectroscopic analyses. The IC50 values of isochromophilones III, IV, V and VI for ACATactivity in an enzyme assay using rat liver microsomes were calculated to be 110, 50, 50 and 120fiM, respectively.

The mutant of Penicillium sp. FO-4259, an arisugacins A and B producing strain, was found to produce a series of metabolites, designated arisugacins C, D, E, F, G and H, which were structurally related to arisugacins A and B. These compoundswere isolated from the culture broth and the physico-chemical and biological properties were examined. The IC50

A new ryanodine-binding inhibitor, verticilide, was isolated from the cultured broth of a fungus, Verticillium sp. FKI-1033. It is a 24-membered ring cyclic depsipeptide, its structure being elucidated as cyclo[(2R)-2-hydroxyheptanoyl-N-methyl-L-alanyl] 4 . Verticilide inhibited ryanodine binding to ryanodine receptors in the cockroach at an IC 50 value of 4.2 lM, whereas inhibition against mouse ryanodine receptors was weak (IC 50 ¼53.9 lM).

No abstract

No abstract