Cereal Chem 56:327 - 332.  |  VIEW ARTICLE
Zein Subunit Homology Revealed Through Amino-Terminal Sequence Analysis.

J. A. Bietz, J. W. Paulis, and J. S. Wall. Copyright 1979 by the American Association of Cereal Chemists, Inc. 

Zein, the prolamine fraction of maize endosperm protein, consists of more than 15 polypeptides differing in isoelectric point and distributed mainly in two molecular weight groups (21,000 and 23,000 daltons). N- Terminal amino acid sequences of mixtures of zein polypeptides from normal and near-isogenic high-lysine opaque-2 (o2) maize were determined to establish structural and genetic relationships. Reduced and alkylated zein polypeptides were subjected to automated sequential Edman degradation and the resulting phenylthiohydantoin deravatives were identified by chromatographic analyses. Sequencing the zein from a normal corn hybrid was successful for 33 residues. Only one or two major amino acids were present at each position, which indicates that most zein polypeptides are homologous in structure. The observed amino acid sequence was H2N-(Thr+Phe)-Ile-(Phe+Ile)-Pro-Gln-Cys-Ser-(Gln+Leu)-Ala-Pro-Ile-Ala-Ile-Leu-Leu-Gln- (Phe+Pro)-Tyr-(Leu+Phe)-Pro-Val-Ala-(Val+Ile)-(Met+Ala)-(Gly+Phe)-(Val+Tyr)-Gln-(Glx+Pro)- (Asn+Leu)-Ala-Val-Leu-Ala-. The two normal corn hybrid zeins sequenced were very similar, but two significant differences occurred: The second zein lacked Phe at position 1 had a Pro/Gln substitution at position 16. Six minor differences in sequence were noted between normal zein and its near-isogenic o2 counter-part, but otherwise the protein fractions were identical. These data support the concept that the genes that control zein synthesis arose through duplication and mutation from a single ancestral gene. Furthermore, they suggest that zein polypeptide chains of 21,000 and 23,000 daltons have similar amino- terminal sequences and that the 23,000-dalton chains have internal insertions or C-terminal extensions of about 20 amino acid residues.