Structural characterization of dioscorin, the major tuber protein of yams, by near infrared Raman spectroscopy

Abstract

As very little is known about the molecular structure of dioscorin, the major storage protein of yam tuber, we report here FT-Raman spectroscopic investigation of this yam protein isolated from D. alata L., for the first time. According to a series of purification and identification by ion-exchange chromatography, gel chromatography, SDS-PAGE, and MALDI-TOF-MS, it shows that the major storage protein is made up of dioscorin A (M.W. ∼33 kDa) and dioscorin B (M.W. ∼31 kDa). Raman spectral results indicate that the secondary structure of dioscorin A is major in α-helix, while dioscorin B belongs to anti-parallel β- sheet. It also shows that the microenvironment of major amino acids including tyrosine, phenylalanine, tryptophan, and methionine, and cysteine exhibit explicit differences between these two components. The conformation of disulfide bonding in dioscorin A predominates in Gauche-Gauche-Trans form, while Gauche-Gauche-Gauche and Trans-Gauche-Trans share the conformation in dioscorin B. Structural resemblance between dioscorin A and crude yam proteins implies that dioscorin A exhibits structural preference even though its content is lower than dioscorin B.