Type I secretion and multidrug efflux: transport through the TolC channel-tunnel

The crystal structure of TolC from Escherichia coli was recently determined to 2.1-Angstrom resolution and shows a unique type of channel architecture : a 12-stranded beta -barrel spans the outer membrane and is attached to a long alpha -helical channel that penetrates far into the periplasm,The stru cture suggests a mechanism for its role in secretion of proteins and in eff lux of toxic small molecules, The TolC export pathway is compared with seve ral import pathways of Gram-negative bacteria where the outer membrane prot ein structures are also known.