Novel intracellular functions of apolipoproteins: the ApoO protein family as constituents of the Mitofilin/MINOS complex determines cristae morphology in mitochondria.

Mitochondria exist in a highly dynamic network that is constantly altered by fusion and fission events depending on various factors such as cellular bioenergetic state and cell cycle. Next to this dynamic nature of the organelle, its cristae membrane also undergoes drastic morphological changes upon physiological or pathological alterations. The Mitofilin/mitochondrial inner membrane organizing system (MINOS) complex was recently reported to ensure mitochondrial architecture and crista junction integrity. Several subunits of this complex are linked to a diverse set of neurological human disorders. Recently, two apolipoproteins, ApoO (APOO) and ApoO-like (APOOL) were suggested to represent constituents of the mammalian Mitofilin/MINOS complex. APOOL was shown to bind the mitochondrial phospholipid cardiolipin (CL) and to interact physically with this complex. In this review we highlight the current view on the mammalian Mitofilin/MINOS complex and focus on APOOL and the role of CL in determining cristae morphology. We will discuss possible functions of the Mitofilin/MINOS complex on lipid transport, on assembly of respiratory supercomplexes, on F1FO-ATP synthase organization, on contact site formation, and on trapping CL within the cristae subcompartment.