title: Anion size modulates the structure of the A state of cytochrome c.
abstract: Several studies have shown that anions induce collapse of acid-denatured cytochrome c into the compact A state having the properties of the molten globule and that the anion charge is the main determinant for the A state stabilization. The results here reported show that the anion size plays a role in determining the overall structure of the A state. In particular, small anions induce formation of an A state in which the native Met80-Fe(III) axial bond is recovered and the nativelike redox properties restored. On the other hand, the A state stabilized by large anions shows a histidine (His26 or His33) as the sixth ligand of the heme-iron, a very weak interaction between Trp59 and the heme propionate, and lacks nativelike redox properties. The two anion-stabilized states show similar stability, indicating that (i) the hydrophobic core (which is equally stabilized by all the anions investigated, independently of their size) is the region that mainly contributes to the macromolecule stabilization, and (ii) the flexible loops are responsible for the spectroscopic (and, thus, structural) and redox differences observed.
authors.affiliation: Dipartimento di Medicina Sperimentale e Scienze Biochimiche; Università di Roma "Tor Vergata", V. Tor Vergata 135, 00133 Roma, Italy. santucci@med.uniroma2.it
authors.forename: R
authors.initials: R
authors.lastname: Santucci
authors.forename: C
authors.initials: C
authors.lastname: Bongiovanni
authors.forename: G
authors.initials: G
authors.lastname: Mei
authors.forename: T
authors.initials: T
authors.lastname: Ferri
authors.forename: F
authors.initials: F
authors.lastname: Polizio
authors.forename: A
authors.initials: A
authors.lastname: Desideri
mesh_terms: D000818:Animals; D000838:Anions; D002942:Circular Dichroism; D003574:Cytochrome c Group / Q000737:chemistry*; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D006736:Horses; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010472:Perchlorates / Q000737:chemistry; D011489:Protein Denaturation; D017510:Protein Folding; D012492:Salts / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D017670:Sodium Compounds / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship; D013696:Temperature; D013816:Thermodynamics; D017186:Titrimetry
chemical_list: D000838:Anions; D003574:Cytochrome c Group; D010472:Perchlorates; D012492:Salts; D017670:Sodium Compounds; D012965:Sodium Chloride; C031068:sodium perchlorate