Abstract
Defensins containing a consensus cystine framework, Cys[1]…Cys[2]X3Cys[3]…Cys[4]… Cys[5]X1Cys[6] (X, any amino acid 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 the cysteine-stabilized α-helix and β-sheet (CSαβ) fold, in which the two invariant motifs, Cys[2]X3Cys[3]/Cys[5]X1Cys[6], 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 patterns, as identified by protein structure modelling. Despite this, they definitely are homologous with 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. The present study 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.
Highlights
Defensins are small cysteine-rich, multifunctional peptides that are extensively distributed in multicellular organisms, including plants, animals and microorganisms
Zymoseptoria tritici is the causal agent of the septoria tritici blotch (STB) in wheat that ranks as one of the most economically important diseases [15,16]
From genomes of three isolates of Z. tritici (IPO323, STIR04 A48b and STIR04 A46b) sequenced recently, we identified a total of 29 genes encoding typical fungal defensin-like peptide (fDLP), which hold the conserved cystine framework (Figure 1A)
Summary
Defensins are small cysteine-rich, multifunctional peptides that are extensively distributed in multicellular organisms, including plants, animals and microorganisms They mostly exert functions in host defence as antimicrobial and/or immune regulatory components some other activities are reported, e.g. protease inhibition and zinc tolerance [1]. Variable residue numbers), they adopt a so-called cysteine-stabilized α-helix and β-sheet (CSαβ) fold, in which the Cys[2]X3Cys[3] motif spans the α-helix and is connected to the C-terminal β-strand covering Cys[5]X1Cys[6] via two disulfide bridges (Cys[2]–Cys[5]/Cys[3]–Cys[6]) and the third disulfide bridge (Cys[1]–Cys[4]) links the N-terminus to the first β-strand (cysteines numbered according to micasin) [7] These three fDLPs belong to the ancient invertebrate-type defensins (AITDs) with c 2017 The Author(s).
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