Plant defensins constitute the innate immune response against pathogens such as fungi and bacteria. Typical plant defensins are small, basic peptides that possess a characteristic three-dimensional fold stabilized by three or four disulfide bridges. In addition to known defensin genes, the Arabidopsis genome comprises > 300 defensin-like genes coding for small cysteine-rich peptides. One of such genes encodes for AtPDFL2.1, a putative antifungal peptide of 55 amino acids, with six cysteine residues in its primary sequence. To understand the functional role of AtPDFL2.1, we carried out antifungal activity assays and determined its high-resolution three-dimensional structure using multidimensional solution NMR spectroscopy. We found that AtPDFL2.1 displays a strong inhibitory effect against Fusarium graminearum (IC50 ≈ 4 μM). This peptide folds in the canonical cysteine-stabilized αβ (CSαβ) motif, consisting of one α-helix and one triple-stranded antiparallel β-sheet stabilized by three disulfide bridges and a hydrophobic cluster of residues within its core where the α-helix packs tightly against the β-sheets. Nuclear spin relaxation measurements show that the structure of AtPDFL2.1 is essentially rigid, with the L3 loop located between β-strands 2 and 3 being more flexible and displaying conformational exchange. Interestingly, the dynamic features of loop L3 are conserved among defensins and are probably correlated to the antifungal and receptor binding activities.
|Original language||English (US)|
|Number of pages||9|
|Journal||Biochimica et Biophysica Acta - Proteins and Proteomics|
|State||Published - Dec 1 2016|
Bibliographical noteFunding Information:
This work is partially supported by the National Institutes of Health ( GM 100310 to G.V.). All NMR data were acquired at the MNMR Center, University of Minnesota. Mass spectrometry was done at the University of Minnesota Center for Mass Spectrometry and Proteomics. The authors thank Dr. Charles Schwieters for help with XPLOR-NIH, Geoffrey Li and Dr. Jonggul Kim for the interpretation of the mass spectrometry data, and Dr. Vitaly V. Vostrikov for data fitting of fast dynamics.
- Antifungal activity
- Conformational dynamics
- Plant defensins
- Solution NMR
- Three-dimensional structure