Mitochondrial β-Barrel Proteins, an Exclusive Club?

Mitochondria, chloroplasts, and Gram-negative bacteria have transporter proteins in their outer membranes called β-barrel proteins. The mechanism of integration of these proteins into the outer membrane of bacteria has been partly elucidated, including the identification of a C-terminal motif consisting of the terminal amino acid phenylalanine and additional hydrophobic residues close to the C terminus (Robert et al., 2006). However, little is known about the sequence characteristics that allow β-barrel proteins to integrate into the outer membrane of mitochondria.