B. Phillippe et al., A POTENT ANTIMICROBIAL PROTEIN FROM ONION SEEDS SHOWING SEQUENCE HOMOLOGY TO PLANT LIPID TRANSFER PROTEINS, Plant physiology, 109(2), 1995, pp. 445-455
An antimicrobial protein of about 10 kD, called Ace-AMP1, was isolated
from onion (Allium cepa L.) seeds. Based on the near-complete amino a
cid sequence of this protein, oligonucleotides were designed for polym
erase chain reaction-based cloning of the corresponding cDNA. The matu
re protein is homologous to plant nonspecific lipid transfer proteins
(nsLTPs), but it shares only 76% of the residues that are conserved am
ong all known plant nsLTPs and is unusually rich in arginine. Ace-AMP1
inhibits all 12 tested plant pathogenic fungi at concentrations below
10 mu g mL(-1). Its antifungal activity is either not at all or is we
akly affected by the presence of different cations at concentrations a
pproximating physiological ionic strength conditions. Ace-AMP1 is also
active on two Gram-positive bacteria but is apparently not toxic for
Cram-negative bacteria and cultured human cells. In contrast to nsLTPs
such as those isolated from radish or maize seeds, Ace-AMP1 was unabl
e to transfer phospholipids from liposomes to mitochondria. On the oth
er hand, lipid transfer proteins from wheat and maize seeds showed lit
tle or no antimicrobial activity, whereas the radish lipid transfer pr
otein displayed antifungal activity only in media with low cation conc
entrations. The relevance of these findings with regard to the functio
n of nsLTPs is discussed.