Introduction of deletion mutations into the VacA p55 domain. (A) Diagram of the full-length 88 kDa VacA protein secreted by H. pylori strain 60190 . p33 (amino acids 1 to 311) and p55 (amino acids 312-821) domains are shown. Mutations encoding single coil deletions within the β-helix of the p55 domain were introduced into the H. pylori chromosomal vacA gene by natural transformation and allelic exchange as described in Methods. The relative position of each single coil deletion is shown. (B) Crystal structure of the p55 VacA domain of H. pylori strain 60190 . The sites of two coils targeted for deletion mutagenesis (amino acids 433-461 and 608-628) are highlighted in red.