The polyprotein allergens of nematodes (NPAs) - Structure at last, but still mysterious

► Nematode polyprotein allergens (NPAs) are immunodominant antigens of parasitic nematodes. ► The atomic structure of the NPA of Ascaris, ABA-1A, has been solved. ► ABA-1A has a compact helical structure with a 3-D architecture of a kind not previously known. ► ABA-1A has two subdomains, each with a hydrophobic binding pocket for small lipid molecules. ► The structure confirms that the fundamental unit of NPAs arose from an ancient duplication event.