Binding mechanism of nonspecific lipid transfer proteins and their role in plant defense.
Plant nonspecific lipid transfer proteins (nsLTPs) are small basic proteins that transport phospholipids between membranes. On the basis of molecular mass, nsLTPs are subdivided into nsLTP1 and nsLTP2. NsLTPs are all helical proteins stabilized by four conserved disulfide bonds. The existence of an internal hydrophobic cavity, running through the molecule, is a typical characteristic of nsLTPs that serves as the binding site for lipid-like substrates. NsLTPs are known to participate in plant defense, but the exact mechanism of their antimicrobial action against fungi or bacteria is still unclear. To trigger plant defense responses, a receptor at the plant surface needs to recognize the complex of a fungal protein (elicitin) and ergosterol. NsLTPs share high structural similarities with elicitin and need to be associated with a hydrophobic ligand to stimulate a defense response. In this study, binding of sterol molecules with rice nsLTPs is analyzed using various biophysical methods. NsLTP2 can accommodate a planar sterol molecule, but nsLTP1 binds only linear lipid molecules. Although the hydrophobic cavity of rice nsLTP2 is smaller than that of rice nsLTP1, it is flexible enough to accommodate the voluminous sterol molecule. The dissociation constant for the nsLTP2/cholesterol complex is approximately 71.21 microM as measured by H/D exchange and mass spectroscopic detection. Schematic models of the nsLTP complex structure give interesting clues about the reason for differential binding modes. Comparisons of NMR spectra of the sterol/rice nsLTP2 complex and free nsLTP2 revealed the residues involved in binding.
Cheng
Chao-Sheng
CS
Department of Life Sciences, National Tsing Hua University, Hsinchu 30043, Taiwan.
Samuel
Dharmaraj
D
Liu
Yaw-Jen
YJ
Shyu
Je-Chyi
JC
Lai
Szu-Ming
SM
Lin
Ku-Feng
KF
Lyu
Ping-Chiang
PC
D020418:Algal Proteins / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D002784:Cholesterol / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D041961:Deuterium Exchange Measurement; D004875:Ergosterol / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D008024:Ligands; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D012275:Oryza / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D010935:Plant Diseases / Q000382:microbiology; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D011485:Protein Binding; D011506:Proteins; D013050:Spectrometry, Fluorescence; D021241:Spectrometry, Mass, Electrospray Ionization
D020418:Algal Proteins; D002352:Carrier Proteins; C109356:LTP2 protein, plant; D008024:Ligands; D010940:Plant Proteins; D011506:Proteins; C085101:elicitin, Phytophthora; C072087:sterol carrier proteins; C010905:dehydroergosterol; D002784:Cholesterol; D004875:Ergosterol