title: The crystal structure of eosinophil cationic protein in complex with 2',5'-ADP at 2.0 A resolution reveals the details of the ribonucleolytic active site.
abstract: Eosinophil cationic protein (ECP) is a component of the eosinophil granule matrix. It shows marked toxicity against helminth parasites, bacteria single-stranded RNA viruses, and host epithelial cells. Secretion of human ECP is related to eosinophil-associated allergic, asthmatic, and inflammatory diseases. ECP belongs to the pancreatic ribonuclease superfamily of proteins, and the crystal structure of ECP in the unliganded form (determined previously) exhibited a conserved RNase A fold [Boix, E., et al. (1999) Biochemistry 38, 16794-16801]. We have now determined a high-resolution (2.0 A) crystal structure of ECP in complex with adenosine 2',5'-diphosphate (2',5'-ADP) which has revealed the details of the ribonucleolytic active site. Residues Gln-14, His-15, and Lys-38 make hydrogen bond interactions with the phosphate at the P(1) site, while His-128 interacts with the purine ring at the B(2) site. A new phosphate binding site, P(-)(1), has been identified which involves Arg-34. This study is the first detailed structural analysis of the nucleotide recognition site in ECP and provides a starting point for the understanding of its substrate specificity and low catalytic efficiency compared with that of the eosinophil-derived neurotoxin (EDN), a close homologue.
mesh_terms: D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D001798:Blood Proteins / Q000737:chemistry* / Q000378:metabolism; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D047091:Eosinophil Granule Proteins; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D012260:Ribonucleases / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D001798:Blood Proteins; D047091:Eosinophil Granule Proteins; C045716:adenosine 2',5'-diphosphate; D000244:Adenosine Diphosphate; D012260:Ribonucleases