title: Analysis of the expression, structure and function of nematode lipid-binding proteins
Creators: name: Prior, Alison Elizabeth
Publisher: name: University of Glasgow
Year: 2002

description: Several classes of lipid-binding protein (LBP) are present in nematodes. These include members of well-characterised families which are widespread in higher animals, but in nematodes have distinct features which set them apart from their counterparts in other organisms. These include an atypical, secreted protein from the FABP (fatty acid-binding) protein family which, in other organisms, are thought to be exclusively intracellular. In addition, two novel classes of LBP, the fatty acid and retinol-binding (FAR) proteins and the nematode polyprotein allergens (NPA), are present in abundance in nematodes. Database similarity searches indicate that these proteins are confined to nematodes and so are possible targets for control and diagnosis. To date, all knowledge on the FAR and NPA proteins has come from studies on animal-parasitic nematodes and nothing is known about the localisation and function of these proteins in plant-parasitic nematodes. In-situ hybridisation studies on FAR, NPA and FABP mRNA localisation in the potato cyst nematode, Globodera pallida, indicated distinct spatial expression patterns for each of these proteins. Immunolocalisation studies indicated that the G. pallida FAR protein (Gp-FAR-1) is present on and rapidly shed from the surface of this nematode and so may interact with host tissues. Spectrofluorimetric studies, using fluorescent probes, showed that Gp-FAR-1 binds long-chain fatty acids and retinol with similar affinities to its counterpart Ov-FAR-1 from the animal-parasitic nematode Onchocerca volvulus and commonly occurring LBPs from other organisms. Surprisingly, mutation of the most conserved residues in Gp-FAR-1 did not ablate ligand-binding but did alter its binding affinities. The surface localisation and rapid shedding of Gp-FAR-1 indicated that, in vivo, this protein is in contact with host tissues and so may be involved in the host-parasite interaction. Lipoxygenase functions as a central enzyme in fatty acid-based defence signalling pathways in plants. Gp-FAR-1 was shown to inhibit the lipoxygenase-mediated peroxidation of fatty acids in vitro, indicating that Gp-FAR-1 could be involved in inhibition and/or evasion of host defence mechanisms. Database similarity searches and structural prediction programs indicated that the FARs and NPAs have stretches of low amino acid identity with a class of vertebrate exchangeable apolipoproteins which share other features with the NPAs. Lipoprotein systems which function in the transport and storage of lipids in oocytes are present in nematodes but little is known about the mechanisms of acquisition, transport and storage of lipids destined for metabolic pathways. Since lipids are the main energy source in nematodes, these lipid transport pathways may be good targets for the development of control strategies. In the absence of recombinant G. pallida NPA protein for use in this work, lipoprotein-binding assays showed that ABA-1, an NPA from the animal-parasitic nematode A. suum, but not Gp-FAR-1, can inhibit aggregation of human low-density lipoprotein in vitro and therefore could function in the disruption of host lipid transport and/or play a role in a previously undescribed lipid transport pathway in nematodes. Evidence in support of the presence of such a pathway in nematodes is presented and discussed.