High-resolution structures of a chitinase complexed with natural product cyclopentapeptide inhibitors: Mimicry of carbohydrate substrate

Abstract

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.

Interactions of a Family 18 Chitinase with the Designed Inhibitor HM508 and Its Degradation Product, Chitobiono-δ-lactone

“…The only other known high affinity inhibitors of family 18 chitinases are the naturally occurring cyclopentapeptides argadin (4) and argifin (23). Structural and enzymological analyses have shown that these peptides bind intimately to the active site of ChiB with affinities in the 10 nM (argadin) and 10 M (argifin) range (24).…”

Crystal Structures of Allosamidin Derivatives in Complex with Human Macrophage Chitinase

“…Chitin is not found in humans but plays a key role in the life cycles of several classes of human pathogens, such as fungi (1), nematodes (2), protozoan parasites (3), and insects (4). Several chitinase inhibitors with biological activity have been identified, such as allosamidin (5), styloguanidines (6), and the cyclic peptides CI-4 (7-9), argifin (10), and argadin (11,12). Allosamidin (see Fig.…”

Effect of Pentoxifylline on Chitinolytic Enzyme Activity in the Eastern Subterranean Termite (Isoptera: Rhinotermitidae)

“…Although few specific NAGase inhibitors have been described, two potent NAGase inhibitors are streptozotocin and O-(2-acetamido-2-deoxy-D-glucopyranosylidene)amino-N-phenylcarbamate (Horsch et al 1991, Konrad et al 2001. Endo-chitinase inhibitors such as allosamidin, argifin, argidin, cyclic dipeptides, and psammaplin A have been studied to evaluate the toxic effects (via topical application and feeding bioassays) in insects-arthropods, including the parasitic blow fly (Lucile cuprina Wiedemann), southern cattle tick (Boophilus microplus Canestrini ), silkworm (Bombyx mori L.), webbing clothes moth (Tineola bisselliella Hummel), the American cockroach (Periplaneta americana L.), the German cockroach (Blattella germanica L.), and the green peach aphid or peach-potato aphid (Myzus persicae Sulzer) (Sakuda et al 1987, Londershausen et al 1996, Blattner et al 1997, Houston et al 2002, Saguez et al 2006, Huang 2012. However, production costs and availability make these chemicals impractical for implementation into an insecticide baiting program.…”