title: Identification of three phases in Onconase refolding.
abstract: Onconase is an extremely stable member of the RNase A superfamily. The increase in the thermodynamic stability by 20 kJ x mol(-1) in comparison to RNase A was expected to result in altered folding behavior. Despite the lack of cis-Pro residues in native Onconase, refolding at low concentrations of guanidine hydrochloride was complex and showed three kinetic phases (fast, medium, and slow), with rate constants differing by a factor of about 10 each. None of the phases could be accelerated by peptidyl-prolyl cis-trans isomerases, pointing to the absence of kinetic phases that are limited by Pro isomerization. The detailed analysis by various probes indicates that the burial of the N-terminal Trp3, which is associated with the restoration of the active site, occurs in the slow phase, i.e. in the last step of refolding. Evidently, in contrast to the folding of RNase A, there is no catalytically active native-like intermediate in the folding of Onconase.
authors.affiliation: Institute of Biochemistry and Biotechnology, Martin-Luther University Halle-Wittenberg, Halle, Germany.
authors.forename: Cindy
authors.initials: C
authors.lastname: Schulenburg
authors.forename: Maria M
authors.initials: MM
authors.lastname: Martinez-Senac
authors.forename: Christian
authors.initials: C
authors.lastname: Löw
authors.forename: Ralph
authors.initials: R
authors.lastname: Golbik
authors.forename: Renate
authors.initials: R
authors.lastname: Ulbrich-Hofmann
authors.forename: Ulrich
authors.initials: U
authors.lastname: Arnold
mesh_terms: D002384:Catalysis; D008958:Models, Molecular; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012260:Ribonucleases / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D012260:Ribonucleases; C058703:ranpirnase