A NOVEL LIPID-BINDING PROTEIN FROM THE CESTODE MONIEZIA-EXPANSA

A lipid-binding protein (LBP) has been purified from the cytosol of th e cestode Moniezia expansa. The native LBP was found to be an oligomer of approx. 250 kDa, consisting of 11 kDa monomers. The LBP bound satu rated and unsaturated fatty acids, but not their CoA derivatives, with K-D values in the range 0.68-7.8 mu M. Cholesterol, dihydroergosterol , bilirubin and retinoids were also bound, but alpha-tocopherol, bile acids, alk-2-enals and alka-2,4-dienals were not. Evidence suggests th at there are two binding sites per subunit, each with different specif icities. The fluorescent fatty acid ethylaminonaphthalene-1-sulphonyl) amino]undecanoic acid (DAUDA) and retinol both showed an additional hi gh-affinity binding site with a density of approximately 0.1 per subun it, suggesting specific binding to the oligomer. The amino acid compos ition of Moniezia LBP was distinct from that of previously characteriz ed fatty acid-binding proteins (FABPs). The protein was not N-terminal ly blocked and yielded a unique amino acid sequence, unrelated to that of any known FABP; there was also evidence of microheterogeneity. Pol yclonal antibodies raised to the Moniezia protein did not cross-react with mammalian, nematode or digenean FABP. The Gibbs free energy for p rotein folding (13.02 kJ/mol; 3.1 kcal/ mol), determined by urea denat uration, was identical for both the native and ligand-bound Moniezia L BP. CD spectra showed that the Moniezia protein contained 36% alpha-he lix and that the secondary structure underwent only minor changes on l igand binding. Moniezia LBP binds a range of anthelmintics, with K-D v alues again in the range 0.66-7.3 mu M. It is possible that, in helmin ths, binding proteins may play a role in determining the specificity a nd site of action of anthelmintics.