Periodic Reporting for period 4 - Chap4Resp (Catching in action a novel bacterial chaperone for respiratory complexes)
Reporting period: 2020-04-01 to 2021-09-30
Although respiration is a vital part of metabolism, the battery occasionally leaks and transfers electrons directly to oxygen, producing reactive oxygen species (ROS) such as H2O2, O2- and OH°. These in turn harm the respiratory complexes by releasing iron from their Fe/S clusters, thus producing even more ROS through the Fenton reaction, and damaging DNA, proteins and lipids, causing ageing and diseases. In addition, many drugs and toxins target respiratory complexes to affect their integrity and inhibit their activity. Conversely, defects in bacterial respiratory complexes that hamper their proton pumping action make the bacterial cell resistant to an important class of antibiotics, aminoglycosides, requiring PMF for uptake.
Understanding assembly pathway of the respiratory complexes is therefore an extremely important goal and a particularly challenging one, because of their membrane location, multisubunit composition and cofactor insertion. For example one largest membrane protein assemblies, the respiratory Complex I from the human mitochondria is composed of 45 subunits. The respiratory Complex I from a bacterium Escherichia coli is built by 14 subunits conserved from bacteria to humans, with 9 Fe/S clusters and a flavin, and, although already very intricate, can be therefore considered as a simplified model of its mitochondrial homolog. The objective of this project is to investigate if the huge E. coli macromolecular cage, the structure of which we recently solved by cryo-electron microscopy (cryoEM), in conjunction with a novel protein cofactor, is a specific chaperone for Fe/S cluster biogenesis and assembly of respiratory complexes, and if yes, would is its mechanism of action.