bims-resufa Biomed News
on Respiratory supercomplex factors
Issue of 2020‒09‒27
two papers selected by
Vera Strogolova
Strong Microbials, Inc

  1. Int J Mol Sci. 2020 Sep 23. pii: E6981. [Epub ahead of print]21(19):
      The transmembrane protein cytochrome c oxidase (CcO) is the terminal oxidase in the respiratory chain of many aerobic organisms and catalyzes the reduction of dioxygen to water. This process maintains an electrochemical proton gradient across the membrane hosting the oxidase. CcO is a well-established model enzyme in bioenergetics to study the proton-coupled electron transfer reactions and protonation dynamics involved in these processes. Its catalytic mechanism is subject to ongoing intense research. Previous research, however, was mainly focused on the turnover of oxygen and electrons in CcO, while studies reporting proton turnover rates of CcO, that is the rate of proton uptake by the enzyme, are scarce. Here, we reconstitute CcO from R. sphaeroides into liposomes containing a pH sensitive dye and probe changes of the pH value inside single proteoliposomes using fluorescence microscopy. CcO proton turnover rates are quantified at the single-enzyme level. In addition, we recorded the distribution of the number of functionally reconstituted CcOs across the proteoliposome population. Studies are performed using proteoliposomes made of native lipid sources, such as a crude extract of soybean lipids and the polar lipid extract of E. coli, as well as purified lipid fractions, such as phosphatidylcholine extracted from soybean lipids. It is shown that these lipid compositions have only minor effects on the CcO proton turnover rate, but can have a strong impact on the reconstitution efficiency of functionally active CcOs. In particular, our experiments indicate that efficient functional reconstitution of CcO is strongly promoted by the addition of anionic lipids like phosphatidylglycerol and cardiolipin.
    Keywords:  electron transfer; membrane protein; proton pump; proton translocation; single enzyme fluorescence microscopy; single molecule
  2. Trends Cell Biol. 2020 Sep 22. pii: S0962-8924(20)30169-0. [Epub ahead of print]
      Mitochondria are dynamic organelles that have essential metabolic and regulatory functions. Earlier studies using electron microscopy (EM) revealed an immense diversity in the architecture of cristae - infoldings of the mitochondrial inner membrane (IM) - in different cells, tissues, bioenergetic and metabolic conditions, and during apoptosis. However, cristae were considered to be largely static entities. Recently, advanced super-resolution techniques have revealed that cristae are independent bioenergetic units that are highly dynamic and remodel on a timescale of seconds. These advances, coupled with mechanistic and structural studies on key molecular players, such as the MICOS (mitochondrial contact site and cristae organizing system) complex and the dynamin-like GTPase OPA1, have changed our view on mitochondria in a fundamental way. We summarize these recent findings and discuss their functional implications.
    Keywords:  MICOS; OPA1; cristae dynamics; remodeling