Anaerobic peroxisomes in Archamoebae

Peroxisomes and mitochondria play a key role in oxygen metabolism. It was widely accepted that the evolutionary adaptation of eukaryotes to anaerobiosis is reflected by the metabolic reduction of mitochondria, and concomitant loss of peroxisomes. The anaerobic protists Mastigamoeba balamuthi (Mb), Pelomyxa schiedti (Ps), and Entamoeba histolytica (Eh) contradict this paradigm. They possess anaerobic types of mitochondria (hydrogenosomes, mitosomes) but also host "anaerobic peroxisomes". Mb/Ps peroxisomes contain a common set of 13 peroxins (Pexs) that retain the core members of each functional category including components of both PTS1 and PTS2 machinery for matrix protein import. However, Eh peroxisomes harbour a reduced set of 7 known Pexs and lacks several components that are highly conserved among most eukaryotic lineages, including components of PTS2 machinery (Pex7), the RING complex (Pex2/10/12), docking complex (Pex13), and peroxisomal membrane protein import receptor (Pex3). Concerning the functional annotation, no clear biochemical context has been found in these anaerobic peroxisomes. They are diverse in enzymatic contents and are involved in various metabolic reactions, while catalase and typical peroxisomal enzymes of fatty acid beta-oxidation are absent. Mb peroxisomes appear to be involved in..