9.B.216 The MICOS Complex Component, Mic60 (Mic60) Family
Mic60 is a component of the MICOS complex, a large protein complex of the mitochondrial inner membrane that plays crucial roles in the maintenance of cristae junctions, inner membrane architecture, and formation of contact sites to the outer membrane. Mic60 promotes protein import via the mitochondrial intermembrane space assembly (MIA) pathway (Rabl et al. 2009; von der Malsburg et al. 2011; Hoppins et al. 2011).
The MICOS complex may mediate the extensive exchange of phospholipids with other cellular organelles such as the endoplasmic reticulum (ER) and vacuolar membranes in yeast. These transfers of phospholipids are thought to occur by a non-vesicular pathway at contact sites between two closely apposed membranes (Michaud et al. 2016). Plastids are able to transfer lipids to mitochondria during phosphate starvation. In Arabidopsis thaliana, a large lipid-enriched complex is called the mitochondrial transmembrane lipoprotein (MTL) complex. The MTL complex contains proteins located in the two mitochondrial membranes, conserved in all eukaryotic cells, such as the TOM complex and AtMic60. Michaud et al. 2016 demonstrated that AtMic60 contributes to the export of phosphatidylethanolamine from mitochondria and the import of galactoglycerolipids from plastids during phosphate starvation. Furthermore, AtMic60 promotes lipid desorption from membranes, likely as an initial step for lipid transfer, and binds to Tom40, suggesting that AtMic60 could regulate the tethering between the inner and outer membranes of mitochondria.