Channel-forming protein essential for import of protein precursors into mitochondria. Forms part of the preprotein translocase complex of the outer mitochondrial membrane (TOM complex) which consists of at least 7 different proteins (TOM5, TOM6, TOM7, TOM20, TOM22, TOM40 and TOM70). Interacts with mitochondrial targeting sequences. Interacts with FCJ1. Belongs to the Tom40 family.