bims-resufa 2019-10-20 papers

Issue of 2019–10–20
two papers selected by
Vera Strogolova, Marquette University

J Mol Biol. 2019 Oct 15. pii: S0022-2836(19)30593-5. [Epub ahead of print]

Allosteric cooperativity in proton energy conversion in A1-type cytochrome c oxidase.

Giuseppe Capitanio, Luigi Leonardo Palese, Francesco Papa, Sergio Papa.

Cytochrome c oxidase (CcO), the CuA, heme a, heme a3, CuB enzyme of respiratory chain, converts the free energy released by aerobic cytochrome c oxidation into a membrane electrochemical proton gradient (ΔμH+). ΔμH+ derives from the membrane anisotropic arrangement of dioxygen reduction to two water molecules and transmembrane proton pumping from a negative (N) space to a positive (P) space separated by the membrane. Spectroscopic, potentiometric analyses and X-ray crystallography, characterize allosteric cooperativity of dioxygen binding and reduction with protonmotive conformational states of CcO. These studies show that allosteric cooperativity stabilizes the favourable conformational state for conversion of redox energy into a transmembrane ΔμH+.

Keywords: Allostery; Cytochromes; Proton pump; Redox enzymes; Respiratory chain

DOI: https://doi.org/10.1016/j.jmb.2019.09.027

EMBO J. 2019 Oct 14. e101056

Individual cristae within the same mitochondrion display different membrane potentials and are functionally independent.

Dane M Wolf, Mayuko Segawa, Arun Kumar Kondadi, Ruchika Anand, Sean T Bailey, Andreas S Reichert, Alexander M van der Bliek, David B Shackelford, Marc Liesa, Orian S Shirihai.

The mitochondrial membrane potential (ΔΨm ) is the main driver of oxidative phosphorylation (OXPHOS). The inner mitochondrial membrane (IMM), consisting of cristae and inner boundary membranes (IBM), is considered to carry a uniform ΔΨm . However, sequestration of OXPHOS components in cristae membranes necessitates a re-examination of the equipotential representation of the IMM. We developed an approach to monitor ΔΨm at the resolution of individual cristae. We found that the IMM was divided into segments with distinct ΔΨm , corresponding to cristae and IBM. ΔΨm was higher at cristae compared to IBM. Treatment with oligomycin increased, whereas FCCP decreased, ΔΨm heterogeneity along the IMM. Impairment of cristae structure through deletion of MICOS-complex components or Opa1 diminished this intramitochondrial heterogeneity of ΔΨm . Lastly, we determined that different cristae within the individual mitochondrion can have disparate membrane potentials and that interventions causing acute depolarization may affect some cristae while sparing others. Altogether, our data support a new model in which cristae within the same mitochondrion behave as independent bioenergetic units, preventing the failure of specific cristae from spreading dysfunction to the rest.

Keywords: MICOS complex; Opa1; crista junction; cristae; membrane potential

DOI: https://doi.org/10.15252/embj.2018101056