What is it about?
Self-nonself discrimination in vertebrates is based on the detection of peptides in proteins of parasites that are not present in the proteins of a host. Therefore, parasitic organisms are under a strong selection pressure to eliminate the maximum possible number of peptides – the potential targets for the hosts’ immunity – from their proteomes. By analysing all sequenced genomes available in public databases in 2015 we found that parasitic organisms, both unicellular and multicellular, use highly impoverished pentapeptide and slightly impoverished tetrapeptide vocabularies in comparison with free-living organisms.
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Why is it important?
1) It shows that the major force influencing the richness of the peptide vocabulary of all current organisms is not a complexity of organisms or the size of their proteomes, but parasitic vs. non-parasitic style of life. 2) It strongly suggests that the most probable targets of T-cells recognition are pentapeptides and tetrapeptides, rather than the longer peptides as it is now mostly believed. This study brings a new understanding to the phenomenon of parasitic molecular mimicry and the evolution of proteomes in general. Moreover, the findings could probably be applied in the process of designing synthetic vaccines.
Perspectives
I have predicted this effect thirty years ago when the mechanism of MHS-based self-nonself discrimination was published. It was rather difficult to proof its existence before enough proteins have been sequenced. The only surprise for me was how strong the effect is – it can be easily recognised by visual inspection of an x-y graph.
Jaroslav Flegr
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This page is a summary of: Parasitism as the main factor shaping peptide vocabularies in current organisms, Parasitology, February 2017, Cambridge University Press,
DOI: 10.1017/s0031182017000191.
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