title: Atomic resolution structures of ribonuclease A at six pH values.
abstract: The diffraction pattern of protein crystals extending to atomic resolution guarantees a very accurate picture of the molecular structure and enables the study of subtle phenomena related to protein functionality. Six structures of bovine pancreatic ribonuclease at the pH* values 5.2, 5.9, 6.3, 7.1, 8.0 and 8.8 and at resolution limits in the range 1.05-1.15A have been refined. An overall description of the six structures and several aspects, mainly regarding pH-triggered conformational changes, are described here. Since subtle variations were expected, a thorough validation assessment of the six refined models was first carried out. Some stereochemical parameters, such as the N[bond]C(alpha)[bond]C angle and the pyramidalization at the carbonyl C atoms, indicate that the standard target values and their weights typically used in refinement may need revision. A detailed comparison of the six structures has provided experimental evidence on the role of Lys41 in catalysis. Furthermore, insights are given into the structural effects related to the pH-dependent binding of a sulfate anion, which mimics the phosphate group of RNA, in the active site. Finally, the results support a number of thermodynamic and kinetic experimental data concerning the role of the disulfide bridge between Cys65 and Cys72 in the folding of RNase A.
authors.affiliation: Centro di Studio di Biocristallografia, CNR, Via Mezzocannone 6, I-80134 Napoli, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Berisio
authors.forename: F
authors.initials: F
authors.lastname: Sica
authors.forename: V S
authors.initials: VS
authors.lastname: Lamzin
authors.forename: K S
authors.initials: KS
authors.lastname: Wilson
authors.forename: A
authors.initials: A
authors.lastname: Zagari
authors.forename: L
authors.initials: L
authors.lastname: Mazzarella
mesh_terms: D000818:Animals; D020134:Catalytic Domain; D002417:Cattle; D003460:Crystallization; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008239:Lysine / Q000378:metabolism; D008958:Models, Molecular; D011487:Protein Conformation; D017510:Protein Folding; D012259:Ribonuclease, Pancreatic / Q000737:chemistry* / Q000378:metabolism; D012997:Solvents / Q000737:chemistry
chemical_list: D004220:Disulfides; D008024:Ligands; D012997:Solvents; D012259:Ribonuclease, Pancreatic; D008239:Lysine