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Effects of additional cysteine residue of Avenin-like b protein by site-directed mutagenesis on dough properties in wheat (Triticum aestivum L.).

Avenin-like b protein is rich in cysteine residues, providing the possibility to form inter-molecular disulfide bonds and then facilitate glutenin polymerization. Site-directed mutagenesis was adopted to produce mutant avenin-like b gene encoding mutant Avenin-like b protein, in which one tyrosine codon at the C-terminal substituted by cysteine codon. Compared with control lines, both transgenic lines with wild-type and mutant avenin-like b genes demonstrated superior dough properties. While compared within the transgenic lines, the mutant lines showed relative weaker dough strength and decreased sodium-dodecyl-sulfate sedimentation volumes (from 69.7 ml in line WT alb-1 to 41.0 ml in line Mut alb-4). These inferior dough properties were accompanied with the lower contents of large-sized glutenin polymers, the decreased particle diameters of glutenin macropolymer (GMP), due to the lower contents of inter-molecular β-sheets (from 39.48% for line WT alb-2 to 30.21% for line Mut alb-3) and the varied contents of disulfide bonds (from 137.37 µmol/g for line WT alb-1 to 105.49 µmol/g for line Mut alb-4) in wheat dough. The extra cysteine might alter the original disulfide bond structure, allowed cysteine residue usually involved in inter-molecular disulfide bond becoming available for intra-chain disulfide bond. Avenin-like b proteins were detected in glutenin macropolymers, providng further evidence for this protein to participate in the polymerization of glutenin. This is the first time to investigate the effect of specific cysteine residue in the Avenin-like b protein on flour quality.