Atomic resolution (0.98 A) structure of eosinophil-derived neurotoxin

Human eosinophil-derived neurotoxin (EDN) is a small, basic protein that belongs to the ribonuclease A superfamily. EDN displays antiviral activity and causes the neurotoxic Gordon phenomenon when injected into rabbits. Although EDN and ribonuclease A have appreciable structural similarity and a conserved catalytic triad, their peripheral substrate-binding sites are not conserved. The crystal structure of recombinant EDN (rEDN) has been determined at 0.98 A resolution from data collected at a low temperature (100 K). We have refined the crystallographic model of the structure using anisotropic displacement parameters to a conventional R-factor of 0.116. This represents the highest resolution structure of rEDN determined to date and is only the second ribonuclease structure to be determined at a resolution greater than 1.0 A. The structure provides a detailed picture of the conformational freedom at the various subsites of rEDN, and the water structure accounts for more than 50% of the total solvent content of the unit cell. This information will be crucial for the design of tight-binding inhibitors to restrain the ribonucleolytic activity of rEDN.