Defensins containing a consensus cystine framework, Cys...CysX3Cys...Cys...CysX1Cys ("X", any amino acids normally except Cys; "...", variable residue numbers), are extensively distributed in a variety of multicellular organisms (plants, fungi and invertebrates) and essentially involved in immunity as microbicidal agents. This framework is a prerequisite for forming a cystine-stabilized α-helix and β-sheet (CSαβ) fold, in which the two invariant motifs, CysX3Cys/CysX1Cys, are key determinants of fold formation. By using a computational genomics approach, we identified a large superfamily of fungal defensin-like peptides (fDLPs) in the phytopathogenic fungal genus - Zymoseptoria , which includes 132 structurally typical and 63 atypical members. These atypical fDLPs exhibit an altered cystine framework and accompanying fold change associated with their secondary structure elements and disulfide bridge pattern, as identified by protein structure modelling. Despite this, they definitely are homologous to the typical fDLPs in view of their precise gene structure conservation and identical precursor organization. Sequence and structural analyses combined with functional data suggest that most of Zymoseptoria fDLPs might have lost their antimicrobial activity. Our work provides a clear example of fold change in the evolution of proteins and is valuable in establishing remote homology among peptide superfamily members with different folds.
- gene discovery
- cysteine-stabilized α-helical and β-sheet fold
- structural evolution
- exon-intron organization
- phytopathogenic fungus
- ©2016 The Author(s)
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