Outer membrane proteins P1 and P2 of Haemophilus influenzae type b: structure and identification of surface-exposed epitopes.

The outer membrane proteins (OMPs) P1 and P2 of Haemophilus influenzae type b exhibit molecular size and antigenic variation. Their structural genes have been cloned from prototype isolates of the most common disease-producing clonal groups. The derived amino acid sequences of P1 from strains of OMP subtypes 1H, 3L, and 6U have three variable regions between highly conserved regions. An immunodominant surface-exposed epitope was identified near the carboxyl terminus of P1 proteins from subtype 1H and 3L strains. The P2 genes from subtype 1H, 1L, and 3L isolates were identical. The P2 gene sequence from a subtype 6U isolate differs from the subtype 1H P2 gene by 13 nucleotides, resulting in 10 amino acid changes. The P2 gene from a subtype 2L isolate differs by 1 nucleotide from the subtype 1H P2 gene, resulting in 1 amino acid change at position 166. Two surface-exposed epitopes of OMP P2 were identified, one each between residues 158 and 174 and residues 319 and 341.