1H, 13C and 15N chemical shift assignments of Na-FAR-1, a helix-rich fatty acid and retinol binding protein of the parasitic nematode Necator americanus

Abstract

The fatty acid and retinol-binding (FAR) proteins are a family of unusual helix-rich lipid binding proteins found exclusively in nematodes, and are secreted by a range of parasites of humans, animals and plants. Na-FAR-1 is from the parasitic nematode <i>Necator americanus</i>, an intestinal blood-feeding parasite of humans. Sequence-specific <SUP>1</SUP>H, <SUP>13</SUP>C and <SUP>15</SUP>N resonance assignments have been obtained for the recombinant 170 amino acid protein, using three-dimensional triple-resonance heteronuclear magnetic resonance experiments. Backbone assignments have been obtained for 99.3 % of the non-proline HN/N pairs (146 out of 147). The amide resonance of T45 was not observed, probably due to rapid exchange with solvent water. A total of 96.9 % of backbone resonances were identified, while 97.7 % assignment of amino acid sidechain protons is complete. All Hα(166), Hβ(250) and Hγ(160) and 98.4 % of the Hδ (126 out of 128) atoms were assigned. In addition, 99.4 % Cα (154 out of 155) and 99.3 % Cβ (143 out of 144) resonances have been assigned. No resonances were observed for the NH<SUB>n</SUB> groups of R93 N<SUB>ε</SUB>H<SUB>ε</SUB>, arginine, N<SUB>η1</SUB>H<SUB>2</SUB>, N<SUB>η2</SUB>H<SUB>2</SUB>, histidine N<SUB>δ1</SUB>H<SUB>δ1</SUB>, N<SUB>ε1</SUB>H<SUB>ε1</SUB> and lysine N<SUB>ζ3</SUB>H<SUB>3</SUB>. Na-FAR-1 has a similar overall arrangement of α-helices to Ce-FAR-7 of the free-living <i>Caeorhabditis elegans</i>, but with an extra C-terminal helix.