1H NMR structural study of free and template-linked antigenic peptide representing the C-terminal region of the heavy chain of influenza virus hemagglutinin.

A 12 kDa template-assembled molecule, incorporating four oxime-linked synthetic peptides representing residues 306-328 of influenza virus hemagglutinin (HA), has been analysed by 1H NMR spectroscopy. The molecule (referred to as the 'tetraoxime') is of interest because it has been shown to elicit a better immune response than the free, monomeric peptide not only in the production of antibodies crossreactive with HA but also in its ability to elicit CD4+ T helper cells. We describe here an NMR structural analysis of (i) the unlinked template molecule and (ii) the free peptide and show that their conformations are not affected upon assembly of the tetraoxime. Our results suggest that the increased immune response observed for the tetraoxime may be due to its greater size and valency compared to that of the free peptide rather than being due to any induced structural effects.