RESUMO
Fatty acid and retinol-binding proteins (FARs) comprise a family of unusual α-helix rich lipid-binding proteins found exclusively in nematodes. They are secreted into host tissues by parasites of plants, animals and humans. The structure of a FAR protein from the free-living nematode Caenorhabditis elegans is available, but this protein [C. elegans FAR-7 (Ce-FAR-7)] is from a subfamily of FARs that does not appear to be important at the host/parasite interface. We have therefore examined [Necator americanus FAR-1 (Na-FAR-1)] from the blood-feeding intestinal parasite of humans, N. americanus. The 3D structure of Na-FAR-1 in its ligand-free and ligand-bound forms, determined by NMR (nuclear magnetic resonance) spectroscopy and X-ray crystallography respectively, reveals an α-helical fold similar to Ce-FAR-7, but Na-FAR-1 possesses a larger and more complex internal ligand-binding cavity and an additional C-terminal α-helix. Titration of apo-Na-FAR-1 with oleic acid, analysed by NMR chemical shift perturbation, reveals that at least four distinct protein-ligand complexes can be formed. Na-FAR-1 and possibly other FARs may have a wider repertoire for hydrophobic ligand binding, as confirmed in the present study by our finding that a range of neutral and polar lipids co-purify with the bacterially expressed recombinant protein. Finally, we show by immunohistochemistry that Na-FAR-1 is present in adult worms with a tissue distribution indicative of possible roles in nutrient acquisition by the parasite and in reproduction in the male.
Assuntos
Interações Hospedeiro-Parasita , Necator americanus/metabolismo , Necatoríase/metabolismo , Proteínas de Ligação ao Retinol/metabolismo , Animais , Sítios de Ligação , Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/patogenicidade , Proteínas de Caenorhabditis elegans/química , Proteínas de Caenorhabditis elegans/metabolismo , Proteínas de Transporte/química , Proteínas de Transporte/metabolismo , Ácidos Graxos/química , Ácidos Graxos/metabolismo , Ligantes , Necator americanus/química , Necator americanus/patogenicidade , Necatoríase/parasitologia , Reprodução , Proteínas de Ligação ao Retinol/químicaRESUMO
Iron-deficiency anemia resulting from intestinal blood loss is the major consequence of hookworm infection. Development of the anemia can be prevented, and it can be treated by administration of iron. Hypoproteinemia, often associated with hookworm infection, may be the result of either protein malnutrition or increased intestinal loss of protein. It is unlikely that the worms cause diffuse morphologic or functional alterations of the intestine. Fortification or supplementation with iron is a practical method to control hookworm disease in endemic areas.