A majority of the proteins targeted to the mitochondria are transported through the translocase of the outer membrane (TOM) complex. Tom70 is a major surface receptor for mitochondrial protein precursors in the TOM complex. To investigate how Tom70 receives the mitochondrial protein precursors, we have determined the crystal structure of yeast Tom70p to 3.0 Å. Tom70p forms a homodimer in the crystal. Each subunit consists primarily of tetratricopeptide repeat (TPR) motifs, which are organized into a right-handed superhelix. The TPR motifs in the N-terminal domain of Tom70p form a peptide-binding groove for the C-terminal EEVD motif of Hsp70, whereas the C-terminal domain of Tom70p contains a large pocket that may be the binding site for mitochondrial precursors. The crystal structure of Tom70p provides insights into the mechanisms of precursor transport across the mitochondrion's outer membrane. © 2006 Nature Publishing Group.
