Mutational analysis of quinolone resistance protein QnrB1.

Alanine substitutions and selected deletions have been used to localize amino acids in QnrB essential for its protective activity. Essential amino acids are found at positions i and i(-2) in the pentapeptide repeat module and in the larger of two loops, where deletion of only a single amino acid compromises activity. Deletion of 10 amino acids at the N terminus is tolerated, but removal of 3 amino acids in the C-terminal dimerization unit destroys activity.