Submitted to: Wheat Genetics International Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 28, 2003
Publication Date: September 1, 2003
Citation: Dupont, F.M., Vensel, W.H., Kasarda, D.D. 2003. Characterization of omega gliadins encoded on chromosme 1a and evidence for post-translational cleavage of omega gliadins by an asparaginyl endoprotease. Wheat Genetics International Symposium Proceedings. 3: 946-948 Interpretive Summary: In order to understand wheat flour quality it is important to understand the many proteins that provide the unique viscoelastic properties of flour dough. New genomic and proteomic techniques make it easier to identify all of the individual proteins in flour and trace their evolutionary relationships. The omega-gliadins (w-gliadins) represent 10% or less of total wheat flour proteins, but they vary in amount more than other gluten proteins, and are unusual in sequence and structure. They have repetitive sequences rich in glutamine and proline, lack cysteine and lack alpha-helical structure. The relative amount of w-gliadins has been reported to change in response to availability of nitrogen and sulfur and in response to environmental conditions. It is possible that changes in w-gliadin amounts or proportions contribute to variability in flour quality. It has been difficult to clone the genes for the w-gliadins. In this paper, we identified, purified and characterized the w-gliadins that are encoded on chromosome 1A of bread wheat. We compared them with w-gliadins from a wild species of wheat that is the ancient donor of the A genome of bread wheat. Evidence from protein sequences and mass spectroscopy suggests that some w-gliadins are modified by an enzyme that cleaves proteins next to an asparagine residue. The experiments are part of a broader research effort to understand the molecular basis for the effects of environment on flour quality.
Technical Abstract: The w-gliadins encoded on chromosome 1 of the A genome were purified from hexaploid bread wheat Triticum aestivum L. (2n=6x=42; AABBDD) cv Butte 86, nullisomic 1D-tetrasomic 1A of cv Chinese Spring (CS N1DT1A) and from T. urartu (2n=2x=14; AA), the A genome donor. The proteins were characterized with respect to molecular mass and N-terminal sequences. RP-HPLC combined with SDS-PAGE of gliadins from CS nullisomic-tetrasomic (NT) lines confirmed the assignment to chromosome 1A. The 1A encoded w-gliadins had apparent molecular masses of 45,000 to 59,000 in SDS PAGE but true molecular masses of only 32,752 to 43,412 determined by mass spectrometry. They were generally smaller than the chromosome 1B or 1D encoded w-gliadins. The N-terminal amino acid sequences for the 1A w-gliadin mature peptides were similar to those for the 1D w-gliadins, barley C-hordeins, and rye w-secalins and unlike the N-terminal sequences for the 1B w-gliadins. Molecular mass and sequence data will be presented supporting the concept that an asparaginyl endoprotease is involved in production of those 1A and 1D w-gliadins with N-terminal sequences beginning with KEL. This is the first evidence suggesting that there is post-translational cleavage of gliadins in addition to cleavage of the signal peptide.