The mitochondrial contact site and cristae organizing system (MICOS) is a multiprotein complex that shapes crista junctions and maintains inner and outer membrane contacts. MICOS coordinates the assembly of electron transport chain complexes, a prerequisite for cellular respiration. Indeed, MICOS is lost in eukaryotes that dispensed with cellular respiration, suggesting that its assembly depends on the presence of an active respiratory chain. Trypanosoma brucei provides a unique system to test this hypothesis as its mitochondrion undergoes developmentally regulated remodeling. In the insect stage, the mitochondrion contains cristae with an active electron transport chain, whereas the mammalian bloodstream form possesses precursor cristae with stub-like morphology that lack respiratory activity. MICOS has been characterized in the insect stage but remains unexamined in the bloodstream form. Here, we demonstrate that all MICOS subunits assemble onto precursor cristae, retaining conserved interactions with both outer and inner membrane protein machineries. This is somewhat unexpected given the co-occurrence of MICOS with active cellular respiration in nature. Furthermore, we identify novel MICOS-associated proteins that are dispensable for its stability, suggesting auxiliary rather than core roles in MICOS function. Together, our findings establish that MICOS assembly precedes cellular respiratory competence and expand its interaction landscape in trypanosomatids.
Michala Boudová, Teresa Wagner, Tomáš Bílý et al.· bioRxiv· 1 citation
Cristae are mitochondrial subcompartments that give the organelle its distinctive appearance. More significantly, mitochondria are the proverbial powerhouses as cristae house the molecular machinery underlying cellular respiration, a process that converts carbon sources into ATP by chemiosmosis. The form of cristae is invariably connected to their bioenergetic function. Here, we review our current understanding of the molecules underpinning crista formation. Not surprisingly, respiratory chain multiprotein complexes are involved in crista formation, with F1FO-ATP synthase dimers being eminent membrane sculptors. But crista formation also requires factors that are not directly part of the respiratory chain. The most ancient is the MICOS complex, which delineates the subcompartment and acts as a hub for crista biogenesis. The mitochondrial inner membrane (IM), from which cristae emerge, is remodelled by different dynamin-related proteins in animals and fungi. Cardiolipin is an integral component of the membranous fabric of the IM. To begin to grasp general design principles underlying crista formation, we synthesize findings from canonical animal and yeast experimental models with those from diverse protists and other eukaryotes. However, how these molecules are orchestrated during crista formation remains a hidden piece in our understanding of how cells differentiate in specialized forms. We highlight the few knowns about crista formation in a handful of organisms to guide research into the many unknowns about how complex subcompartments represented by mitochondrial cristae are formed.
Lilia Colina-Tenorio, Martina Bohuslavová, Alexander W. Bruce et al.· Biochemical Society Transact...· 0 citations