Article,
Crystal structure of an antifungal osmotin-like protein from Calotropis procera and its effects on Fusarium solani spores, as revealed by atomic force microscopy: Insights into the mechanism of action
PHYTOCHEMISTRY, (2015)
DOI: 10.1016/j.phytochem.2015.09.012
Abstract
CpOsm is an antifungal osmotin/thaumatin-like protein purified from the
latex of Calotropis procera. The protein is relatively thermostable and
retains its antifungal activity over a wide pH range; therefore, it may
be useful in the development of new antifungal drugs or transgenic crops
with enhanced resistance to phytopathogenic fungi. To gain further
insight into the mechanism of action of CpOsm, its three-dimensional
structure was determined, and the effects of the protein on Fusarium
solani spores were investigated by atomic force microscopy (AFM). The
atomic structure of CpOsm was solved at a resolution of 1.61 angstrom,
and it contained 205 amino acid residues and 192 water molecules, with a
final R-factor of 18.12% and an R-free of 21.59%. The CpOsm structure
belongs to the thaumatin superfamily fold and is characterized by three
domains stabilized by eight disulfide bonds and a prominent charged
cleft, which runs the length of the front side of the molecule.
Similarly to other antifungal thaumatin-like proteins, the cleft of
CpOsm is predominantly acidic. AFM images of F. solani spores treated
with CpOsm resulted in striking morphological changes being induced by
the protein. Spores treated with CpOsm were wrinkled, and the volume of
these cells was reduced by approximately 80%. Treated cells were
covered by a shell of CpOsm molecules, and the leakage of cytoplasmic
content from these cells was also observed. Based on the structural
features of CpOsm and the effects that the protein produces on F. solani
spores, a possible mechanism of action is suggested and discussed. (C)
2015 Elsevier Ltd. All rights reserved.
