Biosynthesis, cDNA and amino acid sequences of a precursor of conglutin δ, a sulphur-rich protein from Lupinus angustifolius

The biosynthesis of conglutin b has been studied in developing cotyledons of Lupinus angustifolius L. Precursors of conglutin b formed the major sink for [35S]-cysteine incorporated by developing lupin cotyledons, and these precursors were rapidly sequestered into the endoplasmic reticulum. The sequence of a cDNA clone coding for one such precursor of conglutin b was determined. The structure of the precursor polypeptide for conglutin b predicted from the cDNA sequence contained an N-terminal leader peptide of 22 amino acids directly preceding a subunit polypeptide of M r 4520, together with a linking region of 13 amino acids and a subunit polypeptide of Mr 9558 at the C-terminus. The amino acid sequence predicted from the cDNA sequence showed minor variations from that established by sequencing of the protein purified from mature dried seeds (Lilley and Inglis, 1986). These were consistent with the existence of a multi-gene family coding for conglutin b. Comparison of the sequences of
conglutin b with those of other 2S storage proteins showed that the cysteines involved in internal disulphide bridges between the mature subunits of conglutin b, were maintained throughout this family of proteins but that little else was conserved either at the protein or DNA level.