Effect of methionine80 heme coordination on domain swapping of cytochrome c

Abstract

Cytochrome c (cyt c) forms oligomers by domain swapping. It exchanges the C-terminal α-helical region between protomers, and the Met80‒heme iron bond is perturbed significantly in domain-swapped oligomers. The peroxidase activity of cyt c increases by Met80 dissociation from the heme iron, which may trigger apoptosis. This study elucidates the effect of the Met80 heme coordination on cyt c domain swapping by obtaining oligomers for both wild-type (WT) and M80A human cyt c by an addition of ethanol to their monomers, followed by lyophilization and dissolution to buffer, and investigating their dimer properties. The absorption and circular dichroism spectra of WT and M80A cyt c exhibited similar changes upon dimerization, indicating that Met80 does not affect the oligomerization process significantly. According to differential scanning calorimetric measurements, Met80 coordination to the heme iron had an effect on the stabilization of the monomer (ΔH = 16 kcal/mol), whereas no large difference was observed between the dimer-to-monomer dissociation temperatures of WT and M80A cyt c (61.0 °C). The activation enthalpy values were similar and relatively large for the dissociation of both WT and M80A cyt c dimers (WT, 120 ± 10 kcal/mol; M80A, 110 ± 10 kcal/mol), indicating that the dimers suffered large structural changes upon dissociation to monomers independent of the Met80 coordination to the heme iron. These results indicate that cyt c domain swapping may occur regardless of the Met80 coordination, whereas the monomer is stabilized by Met80 but the domain-swapped dimer structure and stability are less affected by the Met80 coordination.

Cytochrome cCatalyzes the Hydrogen Peroxide‐Assisted Oxidative Desulfuration of 2‐Thiouridines in Transfer RNAs

“…Cyt c is a heme protein that exerts peroxidase catalytic activity in the presence of H 2 O 2. Although to date the oxidant generated from cytochrome c has not been identified, the oxoferryl–heme component is thought to be a candidate rather than the hydroxyl radical . Thus, the formation of a peroxidase intermediate of type I (cyt c .+ –Fe IV =O) is suggested [Eq.…”

New Aspects of Cytochrome c: 3D Domain Swapping, Membrane Interaction, Peroxidase Activity, and Met80 Sulfoxide Modification

“…No large difference is observed between the dissociation temperature of the dimer to monomers between wild-type (WT) and M80A cyt c (61.0°C), although the Met80 coordination to the heme iron contributes to the stabilization of the monomer (¦H = ¹16 kcal/mol for the case of human cyt c). 51 The activation enthalpy values for the dissociation of 3D-DS dimers to monomers are similar and relatively large for WT and M80A cyt c (WT, 120 « 10 kcal/mol; M80A, 110 « 10 kcal/mol). Similarly, the activation heat capacity change is large for the dissociation of yeast iso-1-cyt c 3D-DS dimer to monomers.…”

Wheel and Deal in the Mitochondrial Inner Membranes: The Tale of Cytochromecand Cardiolipin

“…Many of the studies above report the loss of the Met80 coordination and at least partial denaturation-or transition to a molten globule state-of Cc when binding to CLcontaining vesicles or liposomes [15,84,93,[95][96][97][109][110][111]. Aside from CL, some other lipids can elicit similar such structural changes in Cc [105].…”

“…However, to our knowledge, the only Cc alkaline structure available (PDB 1LMS; [107]) lacks a channel in which the acyl chain may be lodged, although the heme moiety is more accessible to solvent than the native structure. Another possibility is the formation of Cc oligomers by domain swapping [108,109]. Although these structures are highly variable depending on how the domain swapping is triggered by experimental conditions, a recent analysis has shown they are capable of encompassing an acyl chain [110].…”