Basic Amino Acid Residues of Human Eosinophil Derived Neurotoxin Essential for Glycosaminoglycan Binding

Human eosinophil derived neurotoxin (EDN), a granule protein secreted by activated eosinophils, is a biomarker for asthma in children. EDN belongs to the human RNase A superfamily possessing both ribonucleolytic and antiviral activities. EDN interacts with heparin oligosaccharides and heparin sulfate proteoglycans on bronchial epithelial Beas-2B cells. In this study, we demonstrate that the binding of EDN to cells requires cell surface glycosaminoglycans (GAGs), and the binding strength between EDN and GAGs depends on the sulfation levels of GAGs. Furthermore, in silico computer modeling and in vitro binding assays suggest critical roles for the following basic amino acids located within heparin binding regions (HBRs) of EDN (34)QRRCKN(39) (HBR1), (65)NKTRKN(70) (HBR2), and (113)NRDQRRD(119) (HBR3) and in particular Arg(35), Arg(36), and Arg(38) within HBR1, and Arg(114) and Arg(117) within HBR3. Our data suggest that sulfated GAGs play a major role in EDN binding, which in turn may be related to the cellular effects of EDN.