title: Immobilized cytochrome c bound to cardiolipin exhibits peculiar oxidation state-dependent axial heme ligation and catalytically reduces dioxygen.
abstract: Mitochondrial cytochrome c (cytc) plays an important role in programmed cell death upon binding to cardiolipin (CL), a negatively charged phospholipid of the inner mitochondrial membrane (IMM). Although this binding has been thoroughly investigated in solution, little is known on the nature and reactivity of the adduct (cytc-CL) immobilized at IMM. In this work, we have studied electrochemically cytc-CL immobilized on a hydrophobic self-assembled monolayer (SAM) of decane-1-thiol. This construct would reproduce the motional restriction and the nonpolar environment experienced by cytc-CL at IMM. Surface-enhanced resonance Raman (SERR) studies allowed the axial heme iron ligands to be identified, which were found to be oxidation state dependent and differ from those of cytc-CL in solution. In particular, immobilized cytc-CL experiences an equilibrium between a low-spin (LS) 6c His/His and a high-spin (HS) 5c His/- coordination states. The former prevails in the oxidized and the latter in the reduced form. Axial coordination of the ferric heme thus differs from the (LS) 6c His/Lys and (LS) 6c His/OH(-) states observed in solution. Moreover, a relevant finding is that the immobilized ferrous cytc-CL is able to catalytically reduce dioxygen, likely to superoxide ion. These findings indicate that restriction of motional freedom due to interaction with the membrane is an additional factor playing in the mechanism of cytc unfolding and cytc-mediated peroxidation functional to the apoptosis cascade.
authors: Department of Life Sciences, University of Modena and Reggio Emilia, Via Campi 183, 41125, Modena, Italy.
authors: Antonio
authors: A
authors: Ranieri
authors: Diego
authors: D
authors: Millo
authors: Giulia
authors: G
authors: Di Rocco
authors: Gianantonio
authors: G
authors: Battistuzzi
authors: Carlo A
authors: CA
authors: Bortolotti
authors: Marco
authors: M
authors: Borsari
authors: Marco
authors: M
authors: Sola
mesh_terms: D002308:Cardiolipins / Q000737:chemistry / Q000378:metabolism*; D045304:Cytochromes c / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004563:Electrochemistry; D004800:Enzymes, Immobilized / Q000737:chemistry*; D014644:Genetic Variation; D006418:Heme / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011485:Protein Binding; D013059:Spectrum Analysis, Raman
chemical_list: D002308:Cardiolipins; D004800:Enzymes, Immobilized; D006418:Heme; D045304:Cytochromes c; D010100:Oxygen
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