Channel-forming protein essential for import of protein precursors into mitochondria (PubMed:10980201, PubMed:15347672, PubMed:19401463). Plays a role in the assembly of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) by forming a complex with BCAP31 and mediating the translocation of Complex I components from the cytosol to the mitochondria (By similarity). Forms part of the preprotein translocase complex of the outer mitochondrial membrane (TOM complex) which consists of at least 7 different proteins (TOMM5, TOMM6, TOMM7, TOMM20, TOMM22, TOMM40 and TOMM70). Interacts with mitochondrial targeting sequences (PubMed:10980201, PubMed:15347672). Interacts with TIMM29; linking the TIM22 complex to the TOM complex (By similarity). Forms a complex with BCAP31 (via C-terminus) which mediates the translocation of components of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) from the cytosol to the mitochondria (By similarity). Interacts (via N-terminus) with CYP1A1 (via mitochondrial targeting signal); this interaction is required for CYP1A1 translocation across the mitochondrial outer membrane (PubMed:19401463). Associates with the mitochondria-associated ER membrane via interaction with BCAP31. Belongs to the Tom40 family.