Novel classes of fatty acid and retinol binding protein from nematodes

Parasitic nematodes have recently been found to produce proteins which repr esent two new classes of fatty acid and retinoid binding protein. The first is the nematode polyprotein allergens/antigens (NPAs) which, as their name suggests, are synthesised as large polyproteins which are subsequently cle aved at regularly spaced sites to form multiple copies of a fatty acid bind ing protein of approximately 14.5 kDa. Binding studies using molecular envi ronment-sensitive fluorescent ligands have shown that the binding site is h ighly unusual, producing blue-shifting in fluorescence to an unprecedented degree, suggesting a remarkably non-polar environment and isolation from so lvent water. Computer-based structural predictions and biophysical observat ions have identified the NPAs as highly helical proteins which might form a four helix bundle, so constitute a new class of lipid binding protein from animals. The second class, like the NPAs, binds both fatty acids and retin ol, but with a higher affinity for the latter. These are also highly helica l but are structurally distinct from the NPAs. The biological function of t hese new classes of protein are discussed in the context of both the metabo lic requirements of the parasites and the possible role of the proteins in control of the immune and inflammatory environment of the tissue sites para sitised.