Comparative Genomics Reveals 13 Different Isoforms of Mytimycins (A-M) in Mytilus galloprovincialis

Mytimycins are cysteine-rich antimicrobial peptides that show antifungal properties. These peptides are part of the immune network that constitutes the defense system of the Mediterranean mussel (Mytilus galloprovincialis). The immune system of mussels has been increasingly studied in the last decade due to its great efficiency, since these molluscs, particularly resistant to adverse conditions and pathogens, are present all over the world, being considered as an invasive species. The recent sequencing of the mussel genome has greatly simplified the genetic study of some of its immune genes. In the present work, we describe a total of 106 different mytimycin variants in 16 individual mussel genomes. The 13 highly supported mytimycin clusters (A-M) identified with phylogenetic inference were found to be subject to the presence/absence variation, a widespread phenomenon in mussels. We also identified a block of conserved residues evolving under purifying selection, which may indicate the functional core of the mature peptide, and a conserved set of 10 invariable plus 6 accessory cysteines which constitute a plastic disulfide array. Finally, we extended the taxonomic range of distribution of mytimycins among Mytilida, identifying novel sequences in M. coruscus, M. californianus, P. viridis, L. fortunei, M. philippinarum, M. modiolus, and P. purpuratus.

Automated summary

Mytimycins are cysteine-rich antimicrobial peptides with antifungal properties, part of the immune network of the Mediterranean mussel. Recent genetic studies have identified a total of 106 different mytimycin variants in individual mussel genomes, showing evolutionary trends that contribute to understanding the mussel immune system. Additionally, the distribution of mytimycins has been extended to other Mytilida species, highlighting the importance of these peptides in the defense mechanisms of molluscs.