Anion concentration modulates the conformation and stability of the molten globule of cytochrome c.
Anions induce collapse of acid-denatured cytochrome c into a compact state, the A-state, showing molten globule character. Since structural information on partially folded forms of proteins is important for a deeper understanding of folding mechanisms and of the factors affecting protein stabilization, in this paper we have investigated in detail the effects of anions on the tertiary conformation of the A-state. We have found that the salt-induced collapse of acid-denatured cytochrome c leads to a number of equilibria between high-spin and low-spin heme states and between two types of low-spin states. The two latter states are characterized by conformations leading to a native-like Met-Fe-His axial coordination and a bis-His configuration. The equilibrium between these two A-states is dependent on the concentration and/or size of the anions (i.e. the bigger the anion, the greater its effect). Further, on the basis of fast kinetic data, a kinetic model of the folding process from the acid-unfolded protein to the A-state (at low and high anion concentration) is described.
Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Università di Roma "Tor Vergata", V Montpellier 1, 00133 Rome, Italy.
Federica
F
Sinibaldi
Barry D
BD
Howes
Giulietta
G
Smulevich
Chiara
C
Ciaccio
Massimo
M
Coletta
Roberto
R
Santucci
D000818:Animals; D000838:Anions / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry; D002942:Circular Dichroism; D003574:Cytochrome c Group / Q000737:chemistry* / Q000378:metabolism; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010472:Perchlorates / Q000737:chemistry; D011487:Protein Conformation; D017510:Protein Folding; D017670:Sodium Compounds / Q000737:chemistry; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman; D013696:Temperature; D013997:Time Factors
D000838:Anions; D002712:Chlorides; D003574:Cytochrome c Group; D010472:Perchlorates; D017670:Sodium Compounds; C031068:sodium perchlorate