Characterization of omega gliadins encoded on chromosome 1A and evidence for post-translationai cleavage of omega gliadins by an asparaginyl endoprotease.

摘要

The co-gliadins encoded on chromosome 1 of the A genome were purified from hexaploid wheat Triticum aestivum L. (2n=6x=42; AABBDD) cv Butte 86, nullisomic lD-tetrasomic 1A of cv Chinese Spring (CS HI DTI A) 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 omega-gliadins had apparent molecular masses of 46,000 to 48,000 in SDS PAGE but true molecular masses of only 34,523 to 39,450 by mass spectrometry, and were smaller than chromosome IB or ID encoded co-gliadins. T. urartu omega-gliadins ranged from 34,566 to 43,363. N-terminal amino acid sequences for 1A co-gliadin mature peptides were similar to those for ID co-gliadins, T. urartu co-gliadins, barley C-hordeins, and rye omega-secalins and unlike those for IB co-gliadins. Molecular mass and sequence data support the concept that an asparaginyl endoprotease is involved in production of those 1A and ID co-gliadins with N-terminal sequences beginning with KEL. This is the first evidence suggesting that there is post-translational cleavage of gliadins in addition tocleavage of the signal peptide.