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Molecular diversity of fungal inhibitor cystine knot peptides evolved by domain repeat and fusion

Peptides with the inhibitor cystine knot (ICK) motif are extensively present in animals and plants where they exert a diversity of biological functions. However, few studies have been undertaken on this class of peptides in fungi. In this work, we identify a total of 386 fungal ICK peptides and proteins containing this motif by computational data mining of fungal genome databases, which exhibit 14 different exon-intron structures. According to their domain architectures, these proteins are classified into three distinct structural types, including single domains, tandem repeat domains and fusion domains, in which six families belonging to single or tandem repeat domains show remarkable sequence similarity to those from animals and plants, suggesting their orthologous relationship. Extremely high molecular diversity in fungal ICKs might be attributable to different genetic mechanisms, such as gene/domain duplication and fusion. This work not only enlarges the number of ICK peptides in multicellular organisms, but also uncovers their complex evolutionary history in a specific lineage.