bims-cytox1 Biomed News
on Cytochrome oxidase subunit 1
Issue of 2025–10–12
two papers selected by
Gavin McStay, Liverpool John Moores University
  1. Thermodynamics of the transition from the ferryl (F) state to the oxidized form of the solubilized cytochrome c oxidase: implication for the proton pumping.
  2. Unraveling the pathway of Copper Delivery to Cytochrome c oxidases in the Free-Living Bacterium Caulobacter vibrioides.
  1. Arch Biochem Biophys. 2025 Oct 08. pii: S0003-9861(25)00352-2. [Epub ahead of print] 110638
    Thermodynamics of the transition from the ferryl (F) state to the oxidized form of the solubilized cytochrome c oxidase: implication for the proton pumping.
    Adriana Tomkova, Tereza Sztachova, Jonatan Johannesson, Daniel Jancura, Marian Fabian.
      Two ferryl intermediates have been identified in the membrane-bound respiratory heme-copper oxygen reductases (HCOs) during reduction of O2 to water. Apparently, energy released by reduction of these two ferryl forms is utilized to build the transmembrane electrochemical proton gradient by two mechanisms. One of them, the proton pumping, is the key unresolved problem of the contemporary molecular bioenergetics. Even though the position of these ferryl forms in energy transformation is central, the direct and complete thermodynamic characterization of these intermediates is lacking. Here, thermodynamics of redox transition of one of these ferryl intermediates, the F state, was established by isothermal titration calorimetry (ITC) and density functional theory utilizing one representative of HCOs, bovine cytochrome c oxidase (CcO). In CcOs, the reduction of catalytic cytochrome a3-CuB center is accomplished by electron transfer (ET) from ferrocytochrome c via copper CuA and cytochrome a center. The energy for the pumping is suggested to be released mainly during the transition of the catalytic center of F initiated by ET from cytochrome a. This transfer results in the conversion of Fe(IV)=O to Fe(III) state of heme a3, yielding the oxidized CcO (O). Based on the enthalpy changes determined by ITC and available entropy values for this process, the estimated ΔG0 was found to be -24 kcal/mol, corresponding to the electrode potential of +1.3 V for the F/O couple (pH 8.0, 25 °C). Remarkably, the results indicate that major fraction of energy for the proton pumping is provided by the redox-dependent structural changes of cytochrome a.
    Keywords:  calorimetry; cytochrome oxidase; density functional theory; ferryl intermediate; free energy; proton pumping; reduction potential
    DOI:  https://doi.org/10.1016/j.abb.2025.110638
  2. J Biol Chem. 2025 Oct 06. pii: S0021-9258(25)02638-9. [Epub ahead of print] 110786
    Unraveling the pathway of Copper Delivery to Cytochrome c oxidases in the Free-Living Bacterium Caulobacter vibrioides.
    Hala Kasmo, Jacquie Abolia Tepusa, Rubén Garcia-Dominguez, Chloe Piette, Marc Dieu, Damien Devos, Jean-Yves Matroule.
      Copper (Cu) is an essential micronutrient that serves as a cofactor for many enzymes but becomes toxic when present in excess. In most bacteria, CopA-like P1B-type ATPases mediate Cu detoxification by exporting cytoplasmic Cu to the periplasm or extracellular environment. In this study, we show that Caulobacter vibrioides lacks a canonical CopA-like ATPase but encodes a single FixI/CcoI-type Cu-transporting ATPase, previously implicated in Cu delivery to the cbb3-type cytochrome c oxidase (Cox) in species such as Rhodobacter capsulatus. C. vibrioides harbors two terminal cytochrome c oxidases in its cytoplasmic membrane: an aa3-type and a cbb3-type Cox. We also demonstrate that the activity of cbb3-Cox requires the FixI-type Cu transporter and the periplasmic Cu chaperone PccA. In contrast, aa3-Cox activity depends on PccA and the inner membrane-bound protein CtaG. Since the mechanism of Cu acquisition for aa3-Cox remains largely unknown, we conducted a genetic screen and identified a novel outer membrane TonB-dependent receptor (TccA) that is specifically required for aa3-Cox function. We also showed that cbb3-Cox is upregulated under microaerobic conditions, possibly such as those encountered on solid media where O2 diffusion is limited. Under normoxic conditions, the expression and the activity of cbb3-Cox decrease, and aa3-Cox becomes the predominant terminal oxidase. These findings demonstrate that C. vibrioides differentially utilizes its Cox enzymes in response to O2 availability and relies on a distinct Cu trafficking pathway for their maturation, including an outer membrane component that has not been previously described in bacterial Cu homeostasis.
    Keywords:  Caulobacter vibrioides; Copper; P1B-type ATPase; cytochrome c oxidase; metal transport; oxygen limitation
    DOI:  https://doi.org/10.1016/j.jbc.2025.110786
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