Adaptive evolution and recombination of Rickettsia antigens.
The genus Rickettsia consists of intracellular bacteria that cause a variety of arthropod vectored human diseases. I have examined the evolutionary processes that are generating variation in antigens that are potential vaccine candidates. The surface proteins rOmpA and rOmpB are subject to intense positive natural selection, causing rapid diversification of their amino acid sequences between species. The positively selected amino acids were mapped and cluster together in regions that may indicate the location of functionally important regions such as epitopes. In contrast to the rOmp antigens, there is no evidence of positive selection on the intracytoplasmic antigen PS120 despite low selective constraints on this gene. All three genes showed evidence of recombination between species, and certain sequences are clear chimeras of two parental sequences. However, recombination has been sufficiently infrequent that the phylogenies of the three genes are similar, although not identical.
Jiggins
Francis M
FM
Institute of Cell Animal and Population Biology, Ashworth Laboratories, School of Biology, University of Edinburgh, The King's Buildings, West Mains Road, Edinburgh EH9 3JT, UK. francis.jiggins@ed.ac.uk
D000220:Adaptation, Biological / Q000235:genetics*; D000942:Antigens, Bacterial / Q000235:genetics*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D019143:Evolution, Molecular; D010802:Phylogeny; D011995:Recombination, Genetic; D012281:Rickettsia / Q000235:genetics* / Q000276:immunology; D016415:Sequence Alignment
D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; C404172:Rps120 protein, Rickettsia japonica; C078167:OMPA outer membrane proteins