The Antifungal Protein AFP of Aspergillus giganteusIs an Oligonucleotide/Oligosaccharide Binding (OB) Fold-containing Protein That Produces Condensation of DNA

Álvaro Martı́Nez Del Pozo,Valle Lacadena,José M Mancheño,Nieves Olmo,Mercedes Oñaderra,José G Gavilanes

doi:10.1074/jbc.m207472200

Álvaro Martı́Nez Del Pozo, Valle Lacadena + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m207472200

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Abstract

The antifungal protein AFP is a small polypeptide of 51 amino acid residues secreted by Aspergillus giganteus. Its potent activity against phytopathogenic fungi converts AFP in a promising tool in plant protection. However, no data have been reported regarding the mode of action of AFP. The three-dimensional structure of this protein, a small and compact beta barrel composed of five highly twisted antiparallel beta strands, displays the characteristic features of the oligonucleotide/oligosaccharide binding (OB fold) structural motif. A comparison of the structures of AFP and OB fold-containing proteins shows this structural similarity despite the absence of any significant sequence similarity. AFP, like most OB fold-containing proteins, binds nucleic acids. The protein promotes charge neutralization and condensation of DNA as demonstrated by electrophoretic mobility shift and ethidium bromide displacement assays. Nucleic acid produces quenching of the protein fluorescence emission. This nucleic acid interacting ability of AFP may be related to the antifungal activity of this small polypeptide.

Highlights

Tity) [8] and the antifungal peptide Anafp (56 amino acid residues) secreted by Aspergillus niger (31% sequence identity) [9]
The antifungal protein AFP is a small polypeptide of 51 amino acid residues secreted by Aspergillus giganteus
A fivestranded ␤ barrel capped by an ␣-helix was first noted as a structural motif in some proteins that bind single-stranded nucleic acids or oligosaccharides, and it was termed the oligonucleotide/oligosaccharide binding motif or OB fold [18]

Summary

Introduction

Tity) [8] and the antifungal peptide Anafp (56 amino acid residues) secreted by Aspergillus niger (31% sequence identity) [9]. AFP, like most OB fold-containing proteins, binds nucleic acids. Complete retardation of DNA was produced with no bands of intermediate mobility observed, indicating charge neutralization of the nucleic acid by the protein.

Results

Conclusion