Antifungal activity of synthetic 15-mer peptides based on the Rs-AFP2 (Raphanus sativus antifungal protein 2) sequence.
Plant defensins are a class of cysteine-rich peptides of which several members have been shown to be potent inhibitors of fungal growth. A series of overlapping 15-mer peptides based on the amino acid sequence of the radish antifungal protein Rs-AFP2 have been synthesized. Peptides 6, 7, 8 and 9, comprising the region from cysteine 27 to cysteine 47 of Rs-AFP2 showed substantial antifungal activity against several fungal species (minimal inhibitory concentrations of 30-60 micrograms/mL), but no activity towards bacteria (except peptide 6 at 100 micrograms/mL). The active peptides were shown to be sensitive to the presence of cations in the medium and to the composition and pH of the medium. When present at a subinhibitory concentration (20 micrograms/mL), peptides 1, 7, 8 and 10 potentiated the activity of Rs-AFP2 from 2.3-fold to 2.8-fold. By mapping the characteristics of the active peptide on the structure of Rs-AFP2 as determined by nuclear magnetic resonance, the active region of the antifungal protein appears to involve beta-strands 2 and 3 in combination with the loop connecting those strands. A cyclized synthetic mimic of the loop, cysteine 36 to cysteine 45, was shown to have antifungal activity. Substitution of tyrosine 38 by alanine in the cyclic peptide substantially reduced the antifungal activity, indicating the importance of this residue for the activity of Rs-AFP2 as demonstrated carrier by mutational analysis.
De Samblanx
G W
GW
Katholieke Universiteit Leuven, Heverlee, Belgium.
Fernandez del Carmen
A
A
Sijtsma
L
L
Plasman
H H
HH
Schaaper
W M
WM
Posthuma
G A
GA
Fant
F
F
Meloen
R H
RH
Broekaert
W F
WF
van Amerongen
A
A
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000935:Antifungal Agents / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides; D002118:Calcium / Q000494:pharmacology; D023082:Defensins; D005658:Fungi / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D010940:Plant Proteins / Q000737:chemistry / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D011487:Protein Conformation; D016415:Sequence Alignment
D000596:Amino Acids; D000935:Antifungal Agents; D023181:Antimicrobial Cationic Peptides; D023082:Defensins; D010446:Peptide Fragments; D010456:Peptides, Cyclic; D010940:Plant Proteins; D011188:Potassium; D002118:Calcium