Certain site-directed, nonenzymatically active mutants of the Haemophilus influenzae P4 lipoprotein are able to elicit bactericidal antibodies.

The Haemophilus influenzae P4 lipoprotein (hel) is a potential component of a nontypeable H. influenzae otitis media vaccine. Since P4 is known to be an enzyme, nonenzymatically active forms of recombinant P4 are required. After site-directed mutagenesis of the hel gene, three of the mutated proteins were shown to be vaccine candidates.