FIGURE 7-18 Structural model of one subunit of OmpX, a porin found in the outer membrane of E. coli. All porins are trimeric transmembrane proteins. Each subunit is barrel shaped, with β strands forming the wall and a transmembrane pore in the center. A band of aliphatic (hydrophobic and noncyclic) side chains (yellow) and a border of aromatic (ring-containing) side chains (red) position the protein in the bilayer. See G. E. Schulz, 2000, Curr. Opin. Struct. Biol. 10:443.

[Data from J. Vogt and G. E. Schulz, 1999, Structure 7:1301, PDB ID 1qj8.]