The mitochondrial inner membrane contains a large protein complex crucial for 
membrane architecture, the mitochondrial inner membrane organizing system 
(MINOS). MINOS is required for keeping cristae membranes attached to the inner 
boundary membrane via crista junctions and interacts with protein complexes of 
the mitochondrial outer membrane. To study if outer membrane interactions and 
maintenance of cristae morphology are directly coupled, we generated mutant 
forms of mitofilin/Fcj1 (formation of crista junction protein 1), a core 
component of MINOS. Mitofilin consists of a transmembrane anchor in the inner 
membrane and intermembrane space domains, including a coiled-coil domain and a 
conserved C-terminal domain. Deletion of the C-terminal domain disrupted the 
MINOS complex and led to release of cristae membranes from the inner boundary 
membrane, whereas the interaction of mitofilin with the translocase of the outer 
membrane (TOM) and the sorting and assembly machinery (SAM) were enhanced. 
Deletion of the coiled-coil domain also disturbed the MINOS complex and cristae 
morphology; however, the interactions of mitofilin with TOM and SAM were 
differentially affected. Finally, deletion of both intermembrane space domains 
disturbed MINOS integrity as well as interactions with TOM and SAM. Thus, the 
intermembrane space domains of mitofilin play distinct roles in interactions 
with outer membrane complexes and maintenance of MINOS and cristae morphology, 
demonstrating that MINOS contacts to TOM and SAM are not sufficient for the 
maintenance of inner membrane architecture.