Rice seed storage proteins: A structural insight

Abstract

Rice seed storage proteins, albumin, prolamin and glutelin, ( Oryzae sativa, cv. Basmati 370) were characterized by measurement of their CD and fluorescence spectra in native and denaturing conditions to gain some information about their secondary structure. While rice albumin showed a CD spectrum typical to protein containing β-sheet and β-bends (reverse turns), rice prolamin is predominantly α-helical in nature, which transforms to β-helical nature with the decrease in hydrophobicity. Rice glutelin exhibits a random coil structure with the presence of a small percentage of α-helix secondary structure. During denaturation with guanidine hydrochloride (Gdn.HCl), the relative fluorescence intensity of all three storage proteins shows a decrease at 274 nm and 295 nm indicating unfolding of the protein molecule as is expected. When the fluorescence spectra of prolamin are examined at 274 nm and 295 nm, with a decrease in ethanol concentration (from 70% to 40%, v/v), there is a sudden increase in the relative fluorescence at 50% ethanol concentration, indicating a further folding of the protein molecule before it unfolds at 40% ethanol concentration. The fluorescence data thus substantiates the CD results. This is the first time that the three rice seed storage proteins are examined from the secondary structure point of view.