Abstracts (first author)
In silico peptide-binding predictions of MHC class I reveal similarities across distantly related songbird species, suggesting convergence on the level of protein function
Many songbirds have a large number of transcribed MHC class I genes compared to most mammals. To elucidate the reasons for this large number of genes and to search for non-classical MHC genes in songbirds, we compared songbird MHC class I alleles (α1-α3 domains). By applying phylogenetic analysis, homology modelling and in silico peptide-binding predictions, we could compare both functional and genetic relationships among transcribed genes. We found more pronounced clustering of the MHC class I allomorphs (allele-specific proteins) in regard to their protein function (peptide-binding specificities) compared to their genetic relationships (amino acid sequences), indicating that the high number of alleles is of functional significance.
The MHC class I allomorphs from house sparrow and tree sparrow, species that diverged ten MYA, had overlapping peptide-binding specificities. These similarities across species were also confirmed in phylogenetic analyses, and were similar for genes that we interpret as classical and non-classical. Remarkably, there were also overlapping peptide-binding specificities in the allomorphs from house sparrows and great reed warblers, although these species diverged about 30 MYA. This overlap was not found in a tree based on amino acid sequences. Our interpretation is that convergent evolution on the level of the protein function, possibly driven by selection from shared pathogens, has resulted in allomorphs with similar peptide-binding repertoires, although trans-species evolution in combination with gene conversion cannot be excluded.