The Structural and Evolutionary Relationships of the Prolamin Storage Proteins of Barley, Rye and Wheat

The major endosperm storage proteins of barley, wheat and rye are soluble in aqueous alcohols, either native or after the reduction of disulphide bonds, and can be defined as prolamins. They can be divided into three groups on the basis of their chemical characteristics, notably their molecular mass and amino acid composition, and the chromosomal location of their structural genes. Two of the groups, the high molecular mass prolamins and the sulphur-poor (ω-gliadin-type) prolamins, show clear homology between the three species. The remaining prolamins are characterized by a high content of cysteine. In wheat this is a complex mixture of at least three groups of components that vary in their aggregation properties and N-terminal amino acid sequences. The precise chemical and genetic relationships of those components to each other and to the more clearly defined groups of sulphur-rich prolamins of rye and barley are still not completely understood.