Assembly of Agrostemma githago (corn-cockle) storage proteins and their precursor proteins into oligomers

The major fraction of seed storage proteins of Agrostemma githago (corn-cockle), a non-leguminous dicot, occurs as material with S20,w values of approximately 11S and approximately 2S, and a minor fraction as oligomers with S20,w values of approximately 6.5S. The 11S proteins are of the legumin type and consist of disulphide-linked alpha- and beta-subunits of Mr approximately 39 000 and approximately 23 000 respectively. The oligomeric assembly of the precursor polypeptides of the 11S proteins was examined. The approximately 65 000-Mr precursor polypeptides of two 11S proteins, which consist of 38 000-25 000-Mr subunits and 36 000-22 000-Mr subunits respectively, were assembled into oligomers of approximately 7S and subsequently cleaved. Thereafter the 11S oligomer was formed. The 88 000-Mr precursor of a third 11S protein, which consists of 41 000-23 000-Mr subunits, was assembled into an approximately 8S oligomer and then cleaved, yielding two disulphide-linked intermediates of Mr 59 000 and 24 000. Thereafter, the 11S oligomer was formed. Processing of the 59 000-Mr to the 41 000-Mr polypeptide occurred both in the 8S and in the 11S form.