N-terminal amino acid sequencing of prolamins from wheat and related species

Abstract

The gliadins of common bread wheat (Triticum aestivum L.) make up the major storage protein fraction of grain endosperm and comprise a complex mixture of proteins with similar amino acid compositions and properties¹. Two-dimensional methods of electrophoresis^2,3, in which separations are based mainly on net charge, separate gliadins of a single wheat variety into 30–46 components and there is considerable variation among the electrophoretic patterns of different wheat varieties¹. The gliadins seem to be encoded by clusters of duplicated genes² and may constitute a multigene family⁴. The fact that several purified gliadin components have closely similar N-terminal amino acid sequences^5,6 led us to consider the possibility that, despite the complexity of the mixture, gliadins have sufficient homology in their N-terminal sequences to allow estimation of the homology by sequencing the unfractionated mixture. Here, we provide evidence for two major groups of gliadins in wheat based on N-terminal sequencing, show that similar groups of prolamins (a general term for equivalent proteins in other species) are found in related species of Triticum and Aegilops that may have contributed genomes to polyploid wheats with ABD genome composition, and show that only one of these groups is found in rye (Secale cereale L.).