The gene encoding protein D (hpd) is highly conserved among Haemophilus influenzae type b and nontypeable strains.

The molecular conservation of a surface-exposed lipoprotein, protein D, of Haemophilus influenzae was studied by cloning and sequencing of the gene encoding protein D from three encapsulated type b strains and three nontypeable strains of H. influenzae. These nucleotide sequences were analyzed with previously reported sequences from one type b strain and one nontypeable strain. The nucleotide sequences and the deduced amino acid sequences for protein D were highly conserved. The deduced amino acid sequence (364 amino acids) of protein D from six strains differed only in two amino acids near the C-terminal end. The remaining two strains, one type b and one nontypeable, differed from the consensus sequence in 7 amino acids each. Protein D is 64 and 36% identical and 77 and 56% similar to the glycerophosphodiester phosphodiesterases (GlpQ) of Escherichia coli and Bacillus subtilis.