The mitosome has been detected only in anaerobic or microaerophilic eukaryotes which do not have fully developed mitochondria, and hence do not have the capability of gaining energy from mitochondrial oxidative phosphorylation.[2] The functions of mitosomes, while varied, have not yet been well characterized,[2] but they may be associated with sulfate metabolism and biosynthesis of phospholipids and Fe–S clusters.[2][6][8][9] Mitosomes, like other MROs, likely evolved from mitochondria,[3][10] based on similarities in structure, function, and biochemical signaling pathways,[3][4][5][6][10] and may have convergently evolved across eukaryote lineages.[2][9]
Structure and function
Mitosomes are membrane-bound organelles closely related to mitochondria in structure, though functional overlap is limited.
Giardia intestinalis) have poorly resolved or unexplored functions which are likely related to metabolism and protein transport.[13] Unlike mitochondria, mitosomes appear to lack electron transport chains, N-terminal targeting sequences, and the ability to fuse with each other.[9]
Current knowledge indicates mitosomes probably play a role in
Mastigamoeba balamuthi.[8][14] Recent work indicates that mitosomes participate in the transformation of Entamoeba histolyticatrophozoites into cysts, thereby playing a key role in the pathogenic life cycle of this organism,[14] though the role of mitosomes in pathogenicity is less clear for many other parasitic eukaryotes.[9]
Origin and evolution
In the most widely accepted view, mitosomes are ultimately derived from
endosymbiotic origin.[9][10] Like mitochondria, they have a double membrane and most proteins are delivered to them by a targeting sequence of amino acids.[3][5][6] The targeting sequence is similar to that used for mitochondria and true mitochondrial presequences will deliver proteins to mitosomes.[3] A number of proteins associated with mitosomes have been shown to be closely related to those of mitochondria[4] and hydrogenosomes.[15]
Mitosomes appear to have degeneratively evolved from mitochondria multiple times across eukaryote lineages,
proteobacteria.[8] It has been proposed that MROs such as mitosomes evolved in anoxic marine environments which predominated during the Proterozoic, thus explaining their anaerobic metabolic functionality.[16]
