Steady-state tyrosine fluorescence to study the lipid-binding properties of a wheat non-specific lipid-transfer protein (nsLTP1).

The binding properties of a wheat non-specific lipid-transfer protein (nsLTP1) for different mono- and diacylated lipids was investigated. Lipids varied by their chain length, unsaturation and/or polar head group. In the case of fatty acid or lysophospholipid with a C10 chain length, no interaction can be measured, while poor affinity is reported for a C12 chain length. The dissociation constant (K(d)) is about 0.5 µM independent of chain length from C14 to C18. The same affinity is obtained for C18 fatty acids with one or two unsaturations, whatever the cis-trans double bond isomery. In all cases, the number of binding sites, n, by protein ranges between 1.6 and 1.9, suggesting that two lipids can fit within the protein. omega-Hydroxy-palmitic acid, a natural monomer of cutin polymer, is found to interact with nsLTP1 with a K(d) of 1 µM and n=2. In contrast with previous data that reported the binding of the anionic diacylated phospholipid, DMPG (Sodano et al., FEBS Lett. 416 (1997) 130-134), nsLTP1 is not able to bind dimyristoylphosphatidylcholine, dimyristoylphosphatidic acid, palmitoyl-oleoylphosphatidylcholine or palmitoyl-oleoylphosphatidylglycerol added as liposomes or solubilized in ethanol. However, when both nsLTP1 and lipids are first solubilized in methanol, and then in the buffer, it was evidenced that the protein can bind these lipids. These results suggest that lipid-lipid interactions play an essential role in the binding process of plant nsLTP1 as previously mentioned for other lipid-transfer proteins.