Evolution de la bioénergétiqueEvolution of bioenergetics
Electron Bifurcation (EB)
The molecular process of electron bifurcation (EB) couples the endergonic 1-electron-reduction of a low-potential acceptor by two-electron redox compounds such as flavins or quinones to the exergonic 1-electron-transfer involving the other electron towards a relatively high-potential acceptor molecule. This mechanism represents one of the fundamental principles of free energy conversion in bioenergetics whose basic functional principles still aren’t fully understood (10.3389/fmicb.2018.01357).
Our group has been working on quinone-based electron bifurcation (QBEB) in bc1 and b6f complexes for more than 20 years and more recently also started to investigate this mechanism performed by flavin-containing enzymes, which is an emergent research subject with the first examples reported only a little over 10 years ago (10.1128/JB.01422-07; 10.1128/JB.01417-07).
Reactive minerals and the emergence of life
Our group seeks to understand the evolution of di-iron enzyme reaction centers as found in soluble methane monoxygenase (sMMO) or carbon monoxide dehydrogenase (CODH), and their analgous structural counterparts found in certain reactive naturally occuring minerals such as green rusts, mackinawite, and gregite. Insight into how abiotic geochemical pathways can replicate primative metabolic pathways and self-organize into structures condusive for the continuous production of organic precursors can help us understand how life began it’s inevitable journey to being.
The energy substrates used by prokaryotes are extremely diverse and even include substances that are toxic to most organisms. Among them, Arsenic is emerging as a major bioenergetic microbial substrate used since Archean times. Our research objective is not only to understand the place of Arsenic metabolism in the global evolution of energetic processes and life on earth, but also to unravel the still numerous mysteries of the molecular mechanisms of the functioning of the enzymes involved in the bioenergetic metabolism of Arsenic: arsenite oxidase Aio, alternative arsenite oxidase Arx and arsenate reductase Arr. These questions are addressed according to the specificity of our BIP09 team, i.e. the phylogenetic approach combined with biochemistry (enzymology, purifications), biophysics (optical and EPR spectroscopies) and microbiology.
These lead us to study 1) the molecular determinants of the redox and catalytic properties of Molybdenum (Mo) enzymes other than those involved in the metabolism of arsenic, such as TMAO reductase TorA, Soe TtSDH sulphite oxidases, Psr polysuphite reductase, Ttr tetrathionate reductase 2) the phylogeny of enzymes other than those involved in the metabolism of arsenic, in connection with the latter, for example enzymes for the metabolism of sulphur or nitrate, 3) the metabolic interconnexion of arsenic with selenium, sulphur, or photosynthesis.
We study selected prokaryotic energy conserving chains with the aim of contributing to a comprehensive picture of the diversity of these chains but also of elaborating common features and conserved principles.
The ultimate goal of this approach is to contribute to the elucidation of the origin(s) and evolutionary pathways of biological energy conversion.
All processes in living cells are energy-dependent. Apart from the comparatively inefficient fermentation pathway, this energy is invariably provided by the « Mitchellian » chemiosmotic mechanism, that is, by the conversion of a proton-motive-force (pmf) across a « bioenergetic membrane » into ATP-synthesis via the enzyme ATPase.
In the vast majority of cases, the pmf is produced by the coupling of electron transport to the vectorial translocation of positively charged ions (generally protons, H+) across the bioenergetic membrane (Figure 1). In a few archaeal species, the bioenergetic membrane potential is alternatively built up directly by light-driven ion-translocation performed by the enzyme Bacteriorhodopsin.