title: Structural Zn(II) implies a switch from fully cooperative to partly downhill folding in highly homologous proteins.
abstract: In the funneled landscape, proteins fold to their native states through a stochastic process in which the free energy decreases spontaneously and unfolded, transition, native, and possible intermediate states correspond to local minima or saddle points. Atomic description of the folding pathway appears therefore to be essential for a deep comprehension of the folding mechanism. In metallo-proteins, characterization of the folding pathways becomes even more complex, and therefore, despite their fundamental role in critical biological processes, little is known about their folding and assembly. The study of the mechanisms through which a cofactor influences the protein folding/unfolding reaction has been the rationale of the present study aimed at contributing to the search for cofactors' general roles in protein folding reactions. In particular, we have investigated the folding pathway of two homologous proteins, Ros87, which contains a prokaryotic zinc finger domain, and Ml452-151, lacking the zinc ion. Using a combination of CD, DSC and NMR techniques, we determined the thermodynamics and the structural features, at an atomic level, of the thermal unfolding of Ros87 and compared them to the behavior of Ml452-151. Our results, also corroborated by NMR (1)H/(2)H exchange measurements, show that the presence of the structural Zn(II) in Ros87 implies a switch from the Ml452-151 fully cooperative to a two-step unfolding process in which the intermediate converts to the native state through a downhill barrierless transition. This observation, which has never been reported for any metal ion so far, may have a significant role in the understanding of the protein misfolding associated with the presence of metal ions, as observed in neurodegenerative diseases.
authors.affiliation: Department of Environmental, Biological and Pharmaceutical Science and Technology, Second University of Naples , Via Vivaldi 43, 81100 Caserta, Italy.
authors.forename: Maddalena
authors.initials: M
authors.lastname: Palmieri
authors.forename: Gaetano
authors.initials: G
authors.lastname: Malgieri
authors.forename: Luigi
authors.initials: L
authors.lastname: Russo
authors.forename: Ilaria
authors.initials: I
authors.lastname: Baglivo
authors.forename: Sabrina
authors.initials: S
authors.lastname: Esposito
authors.forename: Fortuna
authors.initials: F
authors.lastname: Netti
authors.forename: Annarita
authors.initials: A
authors.lastname: Del Gatto
authors.forename: Ivan
authors.initials: I
authors.lastname: de Paola
authors.forename: Laura
authors.initials: L
authors.lastname: Zaccaro
authors.forename: Paolo V
authors.initials: PV
authors.lastname: Pedone
authors.forename: Carla
authors.initials: C
authors.lastname: Isernia
authors.forename: Danilo
authors.initials: D
authors.lastname: Milardi
authors.forename: Roberto
authors.initials: R
authors.lastname: Fattorusso
mesh_terms: D002151:Calorimetry; D002942:Circular Dichroism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D011506:Proteins; D015032:Zinc