Potent Human α-Amylase Inhibition by the β-Defensin-like Protein Helianthamide

Abstract

Selective inhibitors of human pancreatic α-amylase (HPA) are an effective means of controlling blood sugar levels in the management of diabetes. A high-throughput screen of marine natural product extracts led to the identification of a potent (<i>K</i>_i = 10 pM) peptidic HPA inhibitor, helianthamide, from the Caribbean sea anemone <i>Stichodactyla helianthus.</i> Active helianthamide was produced in <i>Escherichia coli</i> via secretion as a barnase fusion protein. X-ray crystallographic analysis of the complex of helianthamide with porcine pancreatic α-amylase revealed that helianthamide adopts a β-defensin fold and binds into and across the amylase active site, utilizing a contiguous YIYH inhibitory motif. Helianthamide represents the first of a novel class of glycosidase inhibitors and provides an unusual example of functional malleability of the β-defensin fold, which is rarely seen outside of its traditional role in antimicrobial peptides.