2D-HPLC separation, electrophoretic characterization and N-terminal sequences of oat seed prolamins

Abstract

In common with the alcohol-soluble seed storage proteins (also called prolamins of other cereals, oat avenins are a series of polymorphic molecules belonging to a multigenic family. By using ion-exchange followed by reverse phase HPLC, all the proteins of oat grain soluble in ethanol-water (9:11) have been isolated and purified. They were checked by urea and SDS-PAGE, characterized by N-terminal sequencing and identified by searching in sequence libraries. Beside avenins, the true prolamins, three other low- M r proteins, soluble in ethanol-water, were observed, two of them were identified as α-amylase/trypsin inhibitors which are found in the endosperm of other cereals, and the third one as a novel protein. The microheterogeneity of true avenins are revealed by N-terminal sequencing, although half of them are blocked to Edman degradation. Like other prolamins, avenins exhibit short tandem repeats, heptapeptides slightly different from those found in the Festucoideae subfamily. Their predicted secondary structure reveals successive β-turns which might be arranged in a pseudo-helix structure. In agreement with this arrangement, the hydropathy profile strongly suggests that these pseudo-helices could be associated in a supersecondary structure analogous to that described for maize zein, a structure well-fitted to maximal packing of amino acids in the reserve tissues of the seed.