The active site of ribonuclease A from the crystallographic studies of ribonuclease-A-inhibitor complexes.
The results of X-ray analyses of three ribonuclease-A-nucleotide complexes, at 2.3 A, are reported. A modified purine mononucleotide, 8-oxo-guanosine 2'-phosphate in a syn conformation, binds at the pyrimidine-binding site of the catalytic cleft. Solvent molecules are expelled from the active site due to inhibitor binding. The positions of the side-chains of the active-site residues Gln-11, His-12 and Thr-45 are well defined and do not alter on inhibitor binding. The mobility of Lys-41 is greatly reduced in the protein-nucleotide complexes and the terminal amino group interacts directly with the 2'-phosphate group of the nucleotides. In the complex of the enzyme with a modified pyrimidine, cytidine-N(3)-oxide 2'-phosphate, His-119 is stabilised in the minor site of the native protein [Borkakoti, N., Moss, D.S. and Palmer, R.A. (1982) Acta Crystallogr. B38, 2210-2217], while in the protein-purine derivative the imidazole group is located in the major site. Inhibitor binding induces movements in the side-chains of Lys-7 and Lys-66 which also modify the conformation of the active-site cleft of ribonuclease A.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D002384:Catalysis; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D004722:Endoribonucleases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006639:Histidine / Q000032:analysis; D008239:Lysine / Q000032:analysis; D010179:Pancreas / Q000201:enzymology; D011485:Protein Binding; D011487:Protein Conformation; D012259:Ribonuclease, Pancreatic; D013379:Substrate Specificity; D014961:X-Ray Diffraction
D000596:Amino Acids; D006639:Histidine; D004722:Endoribonucleases; D012259:Ribonuclease, Pancreatic; D008239:Lysine