Three-dimensional crystal structure of human eosinophil cationic protein (RNase 3) at 1.75 angstrom resolution

Eosinophil cationic protein (ECP; RNase 3) is a human ribonuclease found on ly in eosinophil leukocytes that belongs to the RNase A superfamily. This e nzyme is bactericidal, helminthotoxic and cytotoxic to mammalian cells and tissues. The protein has been cloned, heterologously overexpressed, purifie d and crystallized. Its crystal structure has been determined and refined u sing data up to 1.75 Angstrom resolution. The molecule displays the alpha beta folding topology typical for members of the ribonuclease A superfamil y. The catalytic active site residues are conserved with respect to other r ibonucleases of the superfamily but some differences appear at substrate re cognition subsites, which may account, in part, for the low catalytic activ ity. Most strikingly, 19 surface-located arginine residues confer a strong basic character to the protein. The high concentration of positive charges and the particular orientation of the side-chains of these residues may als o be related to the low activity of ECP as a ribonuclease and provides an e xplanation for its unique cytotoxic role through cell membrane disruption. (C) 2000 Academic Press.