FIGURE 1.

Intimin structure and location of double HA tag. A, schematic structure of an intimin dimer. Where experimental structural information is available, the structures are depicted in schematic representation. The periplasmic domain, which mediates dimerization, is colored yellow. The β-barrel domain is blue, the periplasmically located α-helical turn is salmon, and the linker is orange. The extracellular domains, D00-D3, are colored green, red, gray, light blue, and violet, respectively. Protein database identifiers for the structures used in the figure are 2mpw (periplasmic LysM domain), 4e1s (β-barrel domain), and 1f00 (extracellular domains D1–3). B, schematic of the stalled intimin variant, Int HA453. In this mutant, the double HA tag inserted into the N terminus of the passenger domain is surface-exposed, but the C terminus of the protein remains in the periplasm (11). The double HA tag is colored in red, the other features are colored as in panel A. C, insertion site of the double HA tag in Int HA453. A stretch of EPEC intimin sequence is shown spanning the C terminus of the β-barrel domain, the linker sequence, and the beginning of the D00 domain in the passenger. Secondary structure elements (from the intimin β-barrel crystal structure or predicted for the D00 domain) are shown as cylinders for α-helices or arrows for β-strands. The insertion site of the double HA tag in Int HA453 is in the first predicted β-strand of the D00 domain. The coloring corresponds to panels A and B.