|Lawton Jr, John|
Submitted to: United States Japan Natural Resources Protein Panel
Publication Type: Proceedings
Publication Acceptance Date: November 30, 2002
Publication Date: December 1, 2002
Citation: MOMANY, F.A., SESSA, D.J., LAWTON JR, J.W., WILLETT, J.L. A NEW LOOK AT AN OLD PROTEIN: ALPHA-ZEIN. UNITED STATES JAPAN NATURAL RESOURCES PROTEIN PANEL. 2002. Interpretive Summary: Corn is one of the most important commercial plants grown today. The corn granual is made up of starch and a little protein. During the processing of corn to make ethanol, byproducts are produced, primarily arising from Zein type proteins. To add value to the ethanol process, one would like to find new uses for the Zein proteins. Physical data on alpha-Zein had accumulated for years, and with the use of modeling and dynamics simulations a new 3D-structure was discovered. It is hoped that understanding the alpha-Zein 3D-structure will result in new materials of commercial usefulness.
Technical Abstract: Alpha-Zeins are water insoluble storage proteins found in corn protein bodies. Analysis of the protein sequence using probability algorithms, structural studies by circular dichroism, small angle x-ray scattering (SAXS), light scattering, and optical rotatory dispersion results, suggests that the 19 kDa alpha-zein has approximately 50% helical character, made up of nine helical segments of about 20 amino acids with glutamine-rich 'turns' or 'loops'. SAXS and light scattering experiments have suggested that in alcohol/water mixtures alpha-zein exists as an oblong structure with an axial ration of approximately 6:1. Ultracentrifugation, birefringence, dielectric, and viscosity studies indicated that alpha-zein behaves as an asymmetric particle with axial ratios of from 7:1 to 28:1. Previously published models of zein have not been consistent with the experimental data, and for this reason we have re-examined the data and from molecular mechanics and dynamics simulations created a new 3D-structure for Z19. From the amino acid sequence and probability algorithms our analysis suggests that alpha-zein has coiled-coil tendencies resulting in alpha-helices with approximately four residues/turn in their central helical section with the nonpolar residue side-chains forming a hydrophobic face inside a triple helix. We have modeled the nine helical segments of the 19kDa protein into three sets of three interacting helices, with these segments positioned end to end. The resulting 3D-structure is rod-like with dimensions of approximately 110 long and approximately 20 across. This complex structure lengthens with the addition of the N- and C-terminal sections, to give an axial ratio of approximately 6 or 7:1 in agreement with recent light scattering experiments. The natural carotenoid, lutein, is found to fit into the core of the triple helical segments and help stabilize the configuration. Molecular dynamics simulations with methanol molecules as solvent have been carried out to refine the 3D-structure.