LAB_IN_BASEMENT

“...the secret is hidden in the basement...”

Mitochondrial EVOLUTION

BIOGENEsis & DynaMICS of the Mitosomes

TRANSPORT of PROTEINS ACROSS membrAnES

Our lab studies the mitochondrial biogenesis and the protein transport across biological membranes. In particular, we are interested in (i) the extremely reduced mitochondrial forms known as mitosomes and hydrogenosomes, (ii) protein transport across mitochondrial and bacterial membranes. Our general goal is (iii) to understand the events, which enabled the transformation of the bacterial endosymbiont into mitochondria.

All eukaryotic organisms have mitochondria. The simplest forms of mitochondria are called mitosomes, miniature organelles containing handful of proteins, which remotely remind complex threadlike mitochondria of animals and fungi (see figure).

We are interested in the biogenesis, the inheritence and the function of mitosomes in the human pathogen Giardia intestinalis. 

Proteins pass membranes via specialized protein translocases or using the membrane fusions.  Different cellular membranes contain distinct molecular machines, which must specifically recognize and transport individual proteins. We are interested in the mitochondrial protein import and also in the pathogen’s strategies in diverting these pathways in the host cell.

mitochondria of HeLa cells stained with Mitotracker Red

mitosomes of Giardia intestinalis labeled by the antibody raised against IscU, two nuclei are stained with DAPI

Intracellular pathogen Legionella pneumophila secretes bacterial SNARE, which seems to localize to host endoplasmic reticulum during infection.

 

Mitochondrion developed from an endosymbiotic bacterium during the gradual transformation.  As mitochondrial genes had been transferred to the host cell nucleus, the proteins synthesized on the cytosolic ribosomes needed to pass both mitochondrial membranes. Specialized molecular machines were installed into the mitochondrial membranes to allow for substrate specific protein transport. Using the comparative bioinformatics in the combination of functional analyses we endeavor to understand the early events that led to the creation and the evolution of mitochondria.

Molecular machinery for the import of proteins into mitochondria of various eukaryotes can differ dramatically.

While mitochondria of animals and fungi (such as Sacchoromyces) contain multicomponent TOM, TIM and SAM translocases, some eukaryotes contain extremely simplified versions. For several eukaryotic organisms the nature of the mitochondrial translocases remains unknown (Giardia). While some of the participating proteins have bacterial ancestry, most of the translocases represent “eukaryotic inventions”. The arrows depict the direction of protein transport form the cytoplasm into the mitochondrial sub-compartments.