Protein export and drug efflux through bacterial channel-tunnels

The bacterial protein TolC assembles into an a-helical trans-periplasmic tu nnel, which is embedded in the outer membrane by a contiguous beta -barrel channel. TolC and its homologues thus provide large exit ducts for a wide r ange of substrates, including protein toxins and antibacterial drugs, that are engaged by specific recognition proteins in the cytosolic membrane.