Cereal Chem 54:1070 - 1083.  |  VIEW ARTICLE
Wheat Gliadin Homology Revealed through N-Terminal Amino Acid Sequence Analysis.

J. A. Bietz, F. R. Huebner, J. E. Sanderson, and J. S. Wall. Copyright 1977 by the American Association of Cereal Chemists, Inc. 

Amino-terminal sequences of gliadin proteins were examined to reveal evolutionary relations, aid in classification, and relate their sturctures and properties. gamma 1-3-, Beta5-, and alpha8-12- gliadins were isolated from Ponca hard red winter wheat. Disulfide bonds were reduced and alkylated, and the proteins were subjected to automated Edman Degradation. Cleaved amino acids were identified by thin-layer and gas chromatography, spot tests, and amino acid analysis, alpha 8-12- and gamma1-gliadins have the sequence NH2-Val-Arg-Val-Pro-Val-Pro-Gln-Leu-Gln-Pro-Gln-Asn-Pro-Ser-Gln-Gln-Gln-Pro-Gln- Glu- Gln-Val-Pro-Leu-Val-Glx-Glx-; Beta5-gliadin also has this same sequence for at least 22 residues, except that residue 14 could not be identified. Thus gamma1- and beta5-gliadins are homologous to alpha-gliadin, which is known to be toxic to individuals with celiac disease. Gamma2- and gamma3-gliadins each contained two or more polypeptides; the determined partial sequence of gamma2 was NH2-(Asn/Pro)-Ile- (Gly/Gln)-Val-(Asp/VAl/Gln) - (Pro/Gln) - Trp-(Gly/Leu)-Gln-Val-Gln-Trp-(Leu/Val)-(Pro/Gln)-Gln-; that of gamma3 was NH2-(Asn/Pro)-Met-(Gly/Gln)-(Val/Gln)-(Asp/Val)-(Pro/Gln)-(Trp/Gln)-Gly-Gln-Val- Gln-(Trp/Leu)-(Val/Pro)-Pro-Gln-Gln-. Thus, gamma2-3-gliadins differ significantly from alpha8-12-, beta5-, and gamma1-gliadins, but are still homologous to them; to a greater extent they resemble each other. All alpha-, beta-, and gamma-gliadins may originate from one or two ancestral genes. Gliadin classification based solely on electrophoresis fails to reveal these protein relations.