Cys155 of 27 kDa maize gamma-zein is a key amino acid to improve its in vitro digestibility.

Twenty-seven kilodalton gamma-zein is a subclass of the maize zein storage proteins and, due to its localization at the protein body periphery, is critical to digestibility characteristics of all zeins. This protein had low in vitro digestibility, presumably due to its high Cys content (7.35 mol%) that is similar to the hard-to-digest analogous sorghum protein, gamma-kafirin. Therefore, each of the conserved disulfide-bonded Cys' was mutated to create C144A, C148A, C155A, and C156A maize gamma-zein mutants. The C155A showed a remarkable increase in digestibility to proteases - pepsin, chymotrypsin, and trypsin. A high conservation of this Cys among cereal gamma-prolamins indicates the utility of this finding.