Positively Selected Codons in Immune-Exposed Loops of the Vaccine Candidate OMP-P1 of Haemophilus influenzae

• Published in: Journal of molecular evolution 2007-04, Vol.64 (4), p.411-422
• Main Authors: Mes, Ted H. M, van Putten, Jos P. M
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino Acids; Bacteria; Bacterial Outer Membrane Proteins - chemistry; Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - immunology; Codon - genetics; E coli; Epitope; Escherichia coli; Haemophilus influenzae; Haemophilus influenzae - genetics; Haemophilus influenzae - immunology; Haemophilus Vaccines - genetics; Haemophilus Vaccines - immunology; Immune selection; Models, Molecular; Molecular Sequence Data; Outer membrane proteinI; Phylogeny; Proteins; Selection, Genetic; Sequence Alignment; Structural information; Vaccine; Vaccines
• ISSN: 0022-2844; 1432-1432
• DOI: 10.1007/s00239-006-0021-2

The high levels of variation in surface epitopes can be considered as an evolutionary hallmark of immune selection. New computational tools enable analysis of this variation by identifying codons that exhibit high rates of amino acid changes relative to the synonymous substitution rate. In the outer membrane protein P1 of Haemophilus influenzae, a vaccine candidate for nontypeable strains, we identified four codons with this attribute in domains that did not correspond to known or assumed B- and T-cell epitopes of OMP-P1. These codons flank hypervariable domains and do not appear to be false positives as judged from parsimony and maximum likelihood analyses. Some closely spaced positively selected codons have been previously considered part of a transmembrane domain, which would render this region unsuited for inclusion in a vaccine. Secondary structure analysis, three-dimensional structural database searches, and homology modeling using FadL of E. coli as a structural homologue, however, revealed that all positively selected codons are located in or near extracellular looping domains. The spacing and level of diversity of these positively selected and exposed codons in OMP-P1 suggest that vaccine targets based on these and conserved flanking residues may provide broad coverage in H. influenzae.