Positive selection in the evolution of Helicobacter pylori outer membrane proteins

• Autor(es): Nunes, Alexandra ; Ménard, Armelle ; Mégraud, Francis ; Oleastro, Mónica
• Data: 2012
• Identificador Persistente: http://hdl.handle.net/10400.18/1390
• Origem: Repositório Científico do Instituto Nacional de Saúde
• Assunto(s): Helicobacter pylori; OMP; Positive Selection; Infecções Gastrointestinais
• Tipo de Documento: Documento de conferência
• Idioma: Inglês

Descrição

Homologous recombination in Helicobacter pylori has been extensively described to occur via Outer Membrane Proteins (OMPs), regulating protein expression and generating allelic diversity, while the importance of single nucleotide polymorphisms (SNP) remains little studied. We used an OMP-encoding gene, homC, as a model to evaluate the weight of positive selection in the evolution of H. pylori, by using G200 sequences obtained from strains collected worldwide. N-site and branch-site phylogenetic analysis by maximum likelihood models were used to identify specific codons that may be important in homC evolution, and to evaluate the impact of selective pressure on the geographic segregation of strains, respectively. The N-site overall analysis showed that 14 of the 742 (1.9%) homC codons are likely under positive selection (likelihood-ratio test (LRT), p < 10-61). Four of these codons are located in the most variable allelic gene middle region, probably reflecting recombination-derived hitchhiking events. On the other hand, eight codons are located in the more conserved 5¢and 3¢ gene regions, although the significance of this distribution remains to be clarified. Branch-site analysis revealed 36 codons (4.9%) under positive selection (LRT, p < 10-41), showing a non-random distribution, and 89% of these particular codons (p < 10-3) support the phylogenetic segregation of European strains from both African and East Asian strains. The lack of visible recombination within this segment suggests an important biological role of point mutations in the evolution of H. pylori OMPs. In conclusion, homC SNP analysis suggests that, besides recombination, positive selection contributes as well to the evolution of H. pylori OMPs.