A surface-associated retinol- and fatty acid-binding protein (Gp-FAR-1) from the potato cyst nematode Globodera pallida: lipid binding activities, structural analysis and expression pattern

Parasitic nematodes produce at least two structurally novel classes of smal l helix-rich retinol- and fatty-acid-binding proteins that have no counterp arts in their plant or animal hosts and thus represent potential targets fo r new nematicides. Here we describe a protein (Gp-FAR-1) from the plant-par asitic nematode Globodera pallida, which is a member of the nematode-specif ic fatty-acid- and retinol-binding (FAR) family of proteins but localizes t o the surface of this species, placing it in a strategic position for inter action with the host. Recombinant Gp-FAR-1 was found to bind retinol, cis-p arinaric acid and the fluorophore-tagged lipids 11-(dansylamino)undecanoic acid and dansyl-D,L-alpha -amino-octanoic acid. The fluorescence emission c haracteristics of the dansylated analogues indicated that the entire ligand enters the binding cavity. Fluorescence competition experiments showed tha t Gp-FAR-1 binds fatty acids in the range C-11 to C-24, with optimal bindin g at C-15. Intrinsic fluorescence analysis of a mutant protein into which a tryptophan residue had been inserted supported computer-based predictions of the position of this residue at the protein's interior and possibly also at the binding site. Of direct relevance to plant defence systems was the observation that Gp-FAR-1 binds two lipids (linolenic and linoleic acids) t hat are precursors of plant defence compounds and the jasmonic acid signall ing pathway. Moreover, Gp-FAR-1 was found to inhibit the lipoxygenase-media ted modification of these substrates in vitro. Thus not only does Gp-FAR-1 function as a broad-spectrum retinol- and fatty-acid-binding protein, the r esults are consistent with the idea that Gp-FAR-1 is involved in the evasio n of primary host plant defence systems.