Purification and Characterization of a Glycine-rich Protein from the Aleurone Layer of Soybean Seeds

Abstract

Glycine-rich protein (GRP) was extracted with hot water from cell walls of the aleurone layer of soybean seeds and solubilized by pectinase treatment. GRP was purified by Sephadex G-100 gel chromatography, anion exchange HPLC, and reverse-phase HPLC. Two GRP fractions that had almost the same amino acid composition were found by gel chromatography. The high-molecular-mass GRP seems to be an associated form of the low-molecular-mass GRP (30-kDa). Thirty-kDa GRP was separated into a major GRP-I and a minor GRP-II by anion exchange HPLC. The major amino acids of GRP-I purified by reverse-phase HPLC were glycine (68%) and serine (12%). GRP-I contained a small proportion of sugar, approxlmately 9% (w/w), and mannose, arabinose, glucose, xylose, and galactose were included in the sugar moiety. The N-terminal amino acid sequence of GRP-I was a novel polyglycine structure including at least 20 glycine-repeated sequence. The GRP-I might be a novel type of extracellular matrix protein specific to the aleurone layer.