Hydrogenosome

By Levi Clancy for Student Reader on
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Hydrogenosomes metabolize carbohydrates into ATP and H2.

Metabolism in the hydrogenosome is similar to anaerobic bacteria (via enzymes including PFO and ferredoxin) and mitochondria (via Krebs cycle enzymes that convert acetyl CoA into acetate and succinyl CoA which is then converted to succinate and ATP).

Mitochondria and hydrogenosomes likely share an ancestral organelle.

They share similar machinery used for protein translocation; similar signals used for protein translocation; phylogenetically related proteins (Hsp60); and a phylogenetically related ADP/ATP carrier protein.

There are three different theories as to how the hydrogenosome could have arisen: as converted mitochondria; from a common ancestor with mitochondria; or arose independently from mitochondria through different endosymbionts.

Hydrogenosome origins are difficult to pinpoint because unlike mitochondria it has no genome. Over time the endosymbiont that evolved into the hydrogenosome transferred all of its genes to the nucleus.

Hydrogenosome function was identified by protein analysis.

Hydrogenosome function can be characterized as follows: isolate hydrogenosomes; fractionate samples; run on a 1D gel, using Zn chelating chromatography or Na2CO3 extraction; perform a gel trypsin digest; recover the tryptic peptides; use mass spectrometry to get the protein sequence; and run the sequence through databases.

From this, a pie chart can be made of hydrogenosomal proteins' function, revealing most to be small GTP-ases.

TechniqueDescription

Phylogenetics

It turns out that the Hsp60 protein in the hydrogenosome branches with a monophyletic group (99%) composed exclusively of mitochondrial homologues and this branches right next to the proteobacteria group (73%) from which the mitochondria are thought to have arisen.

Characterization

Organelles with a common origin are predicted to have common protein translocation signals and machinery. Incidentally, hydrogenosomal matrix proteins have mitochondrial-like targeting presequences. To determine if this signal is necessary for organelle targeting in vitro and in vivo, membrane translocation components may be characterized. These components must have evolved as the endosymbiont was converted to an organelle, revealing the evolutionary history.