Figure 1.

Structure of the FocA transport path.A, shown is the internal volume of the transport path of an FocA protomer (the inset shows a cartoon of the protomer; Protein Data Bank ID: 3KCU, chain A). The path is narrowed by bulky hydrophobic amino acid residues forming narrow constrictions toward the periplasmic (orange) and the cytoplasmic end (blue). A highly conserved histidine is located in the central region. B, the space-fill display of the constriction residues visualizes that widening side-chain movement is required to allow for substrate passage. C, Western blot showing yeast expression of FocA constriction site mutants probed with an antibody directed against N-terminally engineered hemagglutinin epitope tags. FocA, FNT-type formate transporter from Escherichia coli.