Conformation of the Z19 prolamin by FTIR, NMR, and SAXS

The a zein, the maize storage prolamin, is a mixture of several homologous polypeptides that shows two bands in SIDS-PAGE, called Z19 and Z22. The conformation studies carried out by several authors in this mixture are conflicting. To elucidate these inconsistencies, we analyzed the conformation of the Z19 fraction, extracted from BR451 maize variety by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and small-angle X-ray scattering. The infrared results show that Z19 has 46% of alpha helix and 22% of beta sheet. The fast N-H to N-D exchange measured by H-1 NMR spectroscopy showed that Z19 is not a compact structure. The scattering measurements indicated an extended structure with 12 by 130 Angstrom. With these data, we have modeled the Z19 structure as a hairpin, composed of helical, sheet, turns, and secondary structures, folded back on itself.