Submitted to: Book Chapter
Publication Type: Proceedings
Publication Acceptance Date: 4/20/2003
Publication Date: 6/15/2004
Citation: DUPONT, F.M., VENSEL, W.H., KASARDA, D.D., FIEDLER, D.J. 2003. CHARACTERIZATION OF OMEGA GLIADINS ENCODED ON CHROMOSOME 1A AND EVIDENCE FOR POST-TRANSLATIONAL CLEAVAGE OF OMEGA GLIADINS BY AN ASPARAGINYL ENDOPROTEASE. 8th International Gluten Workshop, Viterbo, Italy. p. 42-45. Interpretive Summary: In order to understand wheat flour quality it is important to know the compositions, sequences and functions of the gluten proteins that provide the unique viscoelastic properties of flour dough. The omega-gliadins (w-gliadins) represent 10% or less of total wheat flour proteins, but they are unusual in sequence and structure, and it is possible that changes in w-gliadin amounts or proportions contribute to variability in flour quality. However, it has been difficult to clone the genes for the w-gliadins. In this paper, we characterized the w-gliadins from Triticum urartu, a wild species of wheat that is the ancient donor of the A genome of bread wheat. We also characterized the w-gliadins from bread wheat. The exact masses of purified w-gliadins were obtained by mass spectroscopy, and N-terminal amino acid sequences were also determined. Pairs of w-gliadins from Triticum urartu differed in mass by 881 Daltons and differed in N-terminal sequence by 8 amino acids. The difference in mass was exactly what was expected if 8 amino acids were cleaved from the protein by a protease that cleaves next to asparagine residues. 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. cv Butte 86, a nullisomic 1D-tetrasomic 1A line of Chinese Spring, and T. urartu, the A genome donor. The proteins were characterized with respect to molecular mass and N-terminal sequences. The 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. The N-terminal amino acid sequences for the 1A w-gliadin mature peptides were similar to those for the 1D w-gliadins, with N-terminal sequences beginning ARE, ARQ or RQ (R-type) or KEL (KEL-type). The KEL-type 1A or 1D-encoded w-gliadins were only present in flour from those wheat varieties that also had R-type 1A or 1D-encoded w-gliadins and only if the R-type w-gliadins had an asparagine prior to the lysine in a PSNKEL motif. Proteins with R- and KEL-type N-terminal sequences that co-eluted in the same HPLC peaks differed by exactly the mass predicted if a short N-terminal peptide was cleaved from the longer R-type w-gliadin by the action of an asparaginyl endoprotease at the NK site. For example, a typical pair of w-gliadins from T. urartu had the N-terminal sequences ARQLNPSNKELQSPQQ and KELQSPQQ, and differed in mass by 881. This is the first evidence suggesting that there is post-translational cleavage of gliadins in addition to cleavage of the signal peptide.