Study of the conformation of γ-zeins in purified maize protein bodies by FTIR and NMR spectroscopy

Abstract

The gamma-zeins are a mixture of 16, 27, and 50-kDa polypeptides which are important in the formation and stabilization of protein bodies (PB). These organelles are used for deposition of zeins, the water-insoluble storage proteins in maize. The nature of the physical interaction between proteins in the assembly and stabilization of PB are fairly well known. It is suggested the repeated hexapeptide sequence (PPPVHL)(8) in the N-terminus is responsible for aggregation of the gamma-zeins on the PB surface. Despite this importance, there is little information about the native conformation of gamma-zeins. In this work, we have analyzed the secondary structures of gamma-zeins in purified protein bodies from two maize cultivars, in the solid state, by FTIR and NMR spectroscopy. The results revealed that gamma-zeins in their physiological state are comprise similar proportions of alpha-helix and beta-sheet, 33 and 31% as determined by FTIR. It was not possible to state if the polyproline II (PPII) conformation is present in the solid-state structure of gamma-zeins, as has been demonstrated for the hexapeptide in solution. Because of the similarity of the solid-state NMR spectra of gamma and alpha-zeins in the alpha carbon region we attributed their contributions to the beta-sheet structures rather than to the PPII conformation or a mixture of these extended structures.